| 1. |
- Adamczyk, Krzysztof, et al.
(author)
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Recombination Strength of Dislocations in High-Performance Multicrystalline/Quasi-Mono Hybrid Wafers During Solar Cell Processing
- 2018
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In: Physica Status Solidi (a) applications and materials science. - Weinheim : Wiley-VCH Verlagsgesellschaft. - 1862-6300 .- 1862-6319. ; 215:2
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Journal article (peer-reviewed)abstract
- Wafers from a hybrid silicon ingot seeded in part for High Performance Multicrystalline, in part for a quasi-mono structure, are studied in terms of the effect of gettering and hydrogenation on their final Internal Quantum Efficiency.The wafers are thermally processed in different groups – gettered and hydrogenated. Afterwards, a low temperature heterojunction with intrinsic thin layer cell process is applied to minimize the impact of temperature. Such procedure made it possible to study the effect of different processing steps on dislocation clusters in the material using the Light Beam Induced Current technique with a high spatial resolution. The dislocation densities are measuredusing automatic image recognition on polished and etched samples. The dislocation recombination strengths are obtained by a correlation of the IQE with the dislocation density according to the Donolato model. Different clusters are compared after different process steps. The results show that for the middle of the ingot, the gettering step can increase the recombination strength of dislocations by one order of magnitude. A subsequent passivation with layers containing hydrogen can lead to a decrease in the recombination strength to levels lower than in ungettered samples.
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| 2. |
- Alnoor, Hatim, et al.
(author)
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Seed layer synthesis effect on the concentration of interface defects and emission spectra of ZnO nanorods/p-GaN light-emitting diode
- 2017
-
In: Physica Status Solidi (a) applications and materials science. - : WILEY-V C H VERLAG GMBH. - 1862-6300 .- 1862-6319. ; 214:1
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Journal article (peer-reviewed)abstract
- As the low-temperature aqueous chemical synthesis (LT-ACS), holds great promises for the synthesis of one-dimensional (1D) ZnO nanostructure-based light-emitting diodes (LEDs) and hence require parameter tuning for optimal performance. N-ZnO nanorods (NRs)/p-GaN heterojunction LEDs have been synthesized by the LT-ACS using ZnO nanoparticle (NPs) seed layers prepared with different precursor solutions. The effect of these seed layers on the interface defect properties and emission intensity of the as-synthesized n-Zn/p-GaN heterojunction LEDs has been demonstrated by spatially resolved cathodoluminescence (CL) and electroluminescence (EL) measurements, respectively. A significant reduction of the interface defects in the n-ZnO NRs/p-GaN heterostructure synthesized from a seed layer prepared from zinc acetate (ZnAc) with a mixture of potassium hydroxide (KOH) and hexamethylenetetramine (HMTA) (donated as ZKH seed) compared with those prepared from ZnAc and KOH (donated as ZK seed) is observed as revealed by spatially resolved CL. Consequently, the LEDs based on n-ZnO NRs/p-GaN prepared from ZKH seed show an improvement in the yellow emission (approximate to 578nm) compared to that based on the ZK seed as deduced from the electroluminescence measurements. The improvement in the yellow EL emission on the ZKH LED probably attributed to the low presence of the non-radiative defect as deduced by light-output current (L-I) characteristics analysis.
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| 3. |
- Amin, Gul, et al.
(author)
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Current-transport studies and trap extraction of hydrothermally grown ZnO nanotubes using gold Schottky diode
- 2010
-
In: PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE. - : WILEY-V C H VERLAG GMBH, PO BOX 10 11 61, D-69451 WEINHEIM, GERMANY. - 1862-6300. ; 207:3, s. 748-752
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Journal article (peer-reviewed)abstract
- High-quality zinc oxide (ZnO) nanotubes (NTs) were grown by the hydrothermal technique on n-Si substrate. The room temperature (RT) current-transport mechanisms of Au Schottky diodes fabricated from ZnO NTs and nanorods (NRs) reference samples have been studied and compared. The tunneling mechanisms via deep-level states was found to be the main conduction process at low applied voltage but at the trap-filled limit voltage (V-TFL) all traps were filled and the space-charge-limited current conduction was the dominating current-transport mechanism. The deep-level trap energy and the trap concentration for; the NTs were obtained as similar to 0.27 eV and 2.1 x 10(16) cm(-3), respectively. The same parameters were also extracted for the ZnO NRs The deep-level states observed crossponds to zinc interstitials (Zn-i), which are responsible for the violet emission.
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| 4. |
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| 5. |
- Arwin, Hans, 1950-, et al.
(author)
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Enhancement in ellipsometric thin film sensitivity near surface plasmon resonance conditions
- 2008
-
In: Physica Status Solidi (a) applications and materials science. - : Wiley-VCH Verlagsgesellschaft. - 1862-6300 .- 1862-6319. ; 205:4, s. 817-820
-
Journal article (peer-reviewed)abstract
- Ellipsometry used in internal reflection mode exhibits enhanced thin film sensitivity if operated close to surface plasmon resonance conditions. Compared to conventional ellipsometry, the changes in the ellipsometric parameter Δ are several orders of magnitude larger. Here, the origin of this large sensitivity is discussed by analysing thin film approximations of the complex reflectance ratio. It is found that the thickness sensitivity in Δ is proportional to the inverse of the difference between the intrinsic and the radiation-induced damping of the surface plasmons.
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| 6. |
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| 7. |
- Beshkova, Milena, et al.
(author)
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Atomic Layer Deposition of AlN on Graphene
- 2021
-
In: Physica Status Solidi (a) applications and materials science. - : WILEY-V C H VERLAG GMBH. - 1862-6300 .- 1862-6319. ; 218:17
-
Journal article (peer-reviewed)abstract
- Graphene is a material with great promise for several applications within electronics. However, using graphene in any such application requires its integration in a stack of thin layers of materials. The ideal structure of graphene has a fully saturated surface without any binding sites for chemisorption of growth species, making film growth on graphene highly challenging. Herein, an attempt to deposit very thin layers of AlN using an atomic layer deposition approach is reported. It is demonstrated using X-ray photoelectron spectroscopy that Al-N are formed in the films deposited on graphene and shown by scanning electron microscopy and atomic force microscopy that the films have an island morphology. These results may be considered promising toward the development of a growth protocol for AlN on graphene and possibly also for 2D AlN fabrication.
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| 8. |
- Blumenau, A.T., et al.
(author)
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The effect of charge on kink migration at 90° partial dislocations in SiC
- 2005
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In: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 202:5, s. 877-882
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Journal article (peer-reviewed)abstract
- SiC bipolar devices show a degradation under forward-biased operation which has been linked with a recombination enhanced motion of one of the two glide dislocations having either Si or C core atoms. We have carried out calculations of the core structures and dynamics of partial dislocations in 3C and 2H-SiC using the density functional based codes DFTB and AIMPRO. After in earlier theoretical work we reported on the structure, energetics and electronic activity of both of the Shockley partials, and on the formation and migration barriers of kinks, in this work we present first results on the effect of charge on the disloction kinks. The calculations give insights into the device degradation mechanism.
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| 9. |
- Bruhn, Benjamin, et al.
(author)
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Fabricating single silicon quantum rods for repeatable single dot photoluminescence measurements
- 2011
-
In: Physica Status Solidi A-applications and materials science. - Malden : Wiley-VCH Verlagsgesellschaft. - 1862-6319. ; 208:3, s. 631-634
-
Journal article (peer-reviewed)abstract
- A fabrication method for a matrix pattern of laterally separated silicon quantum rods was developed, consisting of a three-step recipe utilizing electron beam lithography (EBL), reactive ion etching (RIE), and oxidation. Photoluminescence (PL) measurements -images, spectra, and blinking-verified that the presented method results in a high number of luminescing single silicon quantum rods in well defined positions on the sample. These are suitable for single dot spectroscopy and repeatable measurements, even using different measurement methods and instruments. [GRAPHICS] Colorized scanning electron microscope images of undulating silicon nanowalls for controlled single quantum rod fabrication.
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| 10. |
- Buniatyan, V. V., et al.
(author)
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pH-sensitive properties of barium strontium titanate (BST) thin films prepared by pulsed laser deposition technique
- 2010
-
In: Physica Status Solidi (A) Applications and Materials Science. - : Wiley. - 1862-6319 .- 1862-6300. ; 207:4, s. 824-830
-
Journal article (peer-reviewed)abstract
- pH sensitive properties of barium strontium titianate (BST) high k thin films as alternative gate material for field-effect capacitive (bio-) chemical sensors based on an electrolyte-insulator semiconductor system have been investigated. The BST films of different composition (Ba0.3Sr0.69TiO3, Ba0.25Sr0.75TiO3 and MG doped Ba0.8Sr0.2Mg0.1Ti0.9O3 were deposited by pulsed laser deposition technique from targets farbicated by self-propagating high-temperatures synthesis. The realised sensors have been electrochemically characterised by means of impedance-spectroscopy, capacitance-voltage and constant-capacitance method. The sensors possess a Nernstian-like pH sensitivity in the concentration range between pH 3 and 11 with a response time of 5-10 s. An equivalent circuit model for the BST-based capacitive field-effect sensor is discussed.(C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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| 11. |
- Buyanova, Irina A., et al.
(author)
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Optical and electronic properties of GaInNP alloys - a new material system for lattice matching to GaAs
- 2008
-
In: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 205:1, s. 101-106
-
Journal article (peer-reviewed)abstract
- In this paper we will review our recent results from optical characterization studies of GaInNP. We will show that N incorporation in these alloys affects their structural and defect properties, as well as the electronic structure. The main structural changes include (i) increasing carrier localization due to strong compositional fluctuations, which is typical for all dilute nitrides, and (ii) N-induced long range ordering effects, specific for GaInNP. The observed degradation of radiative efficiency of the alloys upon increasing N content is attributed to formation of several defects acting as centres of efficient non-radiative recombination. One of the defects is identified as a complex involving a Ga interstitial atom. N incorporation is also found to change the band line up from the type I in the GaInP/GaAs structures to the type 11 in the GaInNP/GaAs heterojunctions with [N] > 0.5%. For the range of N compositions studied ([N] <= 2%), a conduction band offset at the GaInNP/GaAs interface is found to nearly linearly depend on [N] at -0.10 eV/%, whereas the valence band offset remains unaffected. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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| 12. |
- Carva, Karel, et al.
(author)
-
Spin-mixing conductances : The influence of disorder
- 2008
-
In: Physica status solidi A, Applications and materials science. - : Wiley. - 1862-6300. ; 205:8, s. 1805-1808
-
Journal article (peer-reviewed)abstract
- Spin transfer torque exerted on a magnetic layer can be viewed as a linear response to the spin accumulation inside an adjacent non-magnetic layer, information about their response coefficient is provided by the complex spin-mixing conductance C-mix. Substitutional disorder is known to affect the spin-dependent charge conductances and often reduces strongly the magnetoresistance. Here, we examine its impact on C-mix of several selected realistic systems. Recently predicted oscillations of C-mix as a function of ferromagnetic layer thickness in Ni based junctions might be suppressed by interface interdiffusion, but presented ab initio calculations disprove this possibility. Halfmetallic character of the Heusler compound Co(2)Mnsi is destroyed by often encountered antisite disorder; however the impact of this disorder to the predicted C-mix is rather weak. Diluted magnetic semiconductor (Ga,Mn)As is an intrinsically disordered system the analysis of calculations shows that the variation of C-mix with substitutional Mn content can be understood in terms of the associated change of the number of carriers, whereas the variation with lattice defects is more complex.
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| 13. |
- Carvalho, Alexandra, et al.
(author)
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Light induced degradation in B doped Cz-Si solar cells
- 2012
-
In: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 209:10, s. 1894-1897
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Journal article (peer-reviewed)abstract
- We analyse the formation energy of interstitial boron (Bi) and the properties of the defect resulting from its association with an oxygen dimer (BiO2i) to evaluate the possibility that it may be the slow-forming centre responsible for the light-induced degradation of B-doped Si solar cells. However, we find that the formation energy of Bi is too high, and therefore its concentration is negligible. Moreover, we find that the lowest energy form of BiO2i is a shallow donor, and the deep donor form is high in energy. Lowest energy structure of the BiO2i defect.
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| 14. |
- Carvalho, Alexandra, et al.
(author)
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P-doping of Si nanoparticles : the effect of oxidation
- 2012
-
In: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 209:10, s. 1847-1850
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Journal article (peer-reviewed)abstract
- The radial dependence of the formation energy of substitutional phosphorus in silicon nanoparticles covered by an amorphous oxide shell is analysed using local density functional theory calculations. It is found that P+ is more stable at the silicon core. This explains the experimental observation of segregation of phosphorus to the Si-rich regions in a material consisting of Si nanocrystals embedded in a SiO2 matrix [Perego et al., Nanotechnology 21, 025602 (2010)]. Formation energy of positively charged substitutional phosphorus in a 1.5 nm diameter Si nanoparticle covered by a ∼2 nm-thick amorphous SiO2 shell, as a function of its distance to the centre.
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| 15. |
- Chen, Ding-Yuan, et al.
(author)
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Impact of the Channel Thickness on Electron Confinement in MOCVD-Grown High Breakdown Buffer-Free AlGaN/GaN Heterostructures
- 2023
-
In: Physica Status Solidi (A) Applications and Materials Science. - : Wiley. - 1862-6319 .- 1862-6300. ; 220:16
-
Journal article (peer-reviewed)abstract
- The 2D electron gas (2DEG) confinement on high electron mobility transistor (HEMT) heterostructures with a thin undoped GaN channel layer on the top of a grain-boundary-free AlN nucleation layer is studied. This is the first time demonstration of a buffer-free epi-structure grown with metal-organic chemical vapor deposition with thin GaN channel thicknesses, ranging from 250 to 150 nm, without any degradation of the structural quality and 2DEG properties. The HEMTs with a gate length of 70 nm exhibit good DC characteristics with peak transconductances of 500 mS mm(-1) and maximum saturated drain currents above 1 A mm(-1). A thinner GaN channel layer improves 2DEG confinement because of the enhanced effectiveness of the AlN nucleation layer acting as a back-barrier. An excellent drain-induced barrier lowering of only 20 mV V-1 at a V-DS of 25 V and an outstanding critical electric field of 0.95 MV cm(-1) are demonstrated. Good large-signal performance at 28 GHz with output power levels of 2.0 and 3.2 W mm(-1) and associated power-added efficiencies of 56% and 40% are obtained at a V-DS of 15 and 25 V, respectively. These results demonstrate the potential of sub-100 nm gate length HEMTs on a buffer-free GaN-on-SiC heterostructure.
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| 16. |
- Chey, Chan Oeurn, et al.
(author)
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Fast synthesis, morphology transformation, structural and optical properties of ZnO nanorods grown by seed-free hydrothermal method
- 2014
-
In: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 211:11, s. 2611-2615
-
Journal article (peer-reviewed)abstract
- A fast and low cost seed-free hydrothermal synthesis method to synthesize zinc oxide (ZnO) nanorods with controllable morphology, size and structure has been developed. Ammonia is used to react with water to tailor the ammonium hydroxide concentration, which provides a continuous source of OH− for hydrolysis and precipitation of the final products. Hence, allowing ZnO nanorods to growth on large areas of metal (Au and Ag coated glass), p-type Si and organic flexible (PEDOT: PSS) substrates. Increasing the growth time, the morphology transforms from pencil-like to hexagonal shape rod-like morphology. Within one hour the length of the ZnO nanorods has reached almost 1 µm. The optical characteristics has shown that the grown ZnO nanorods are dominated by two emission peaks, one is in the UV range centered at 381 nm and other one with relatively high intensity appears in the visible range and centered at 630 nm. While the growth duration was increased from 2 h to 6 h, the optical band gap was observed to increase from 2.8 eV to 3.24 eV, respectively. This fast and low cost method is suitable for LEDs, UV-photodetector, sensing, photocatalytic, multifunctional devices and other optoelectronic devices, which can be fabricated on any substrates, including flexible and foldable substrates.
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| 17. |
- Chulapakorn, Thawatchart, 1988-, et al.
(author)
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Impact of H-uptake by forming gas annealing and ion implantation on photoluminescence of Si-nanoparticles
- 2018
-
In: Physica Status Solidi (a) applications and materials science. - : John Wiley & Sons. - 1862-6300 .- 1862-6319. ; 215:3
-
Journal article (peer-reviewed)abstract
- Silicon nanoparticles (SiNPs) are formed by implanting 70 keV Si+ into a SiO2-film and subsequent thermal annealing. SiNP samples are further annealed in forming gas. Another group of samples containing SiNP is implanted by 7.5 keV H+ and subsequently annealed in N2-atmosphere at 450 °C to reduce implantation damage. Nuclear reaction analysis (NRA) is employed to establish depth profiles of the H-concentration. Enhanced hydrogen concentrations are found close to the SiO2surface, with particularly high concentrations for the as-implanted SiO2. However, no detectable uptake of hydrogen is observed by NRA for samples treated by forming gas annealing (FGA). H-concentrations detected after H-implantation follow calculated implantation profiles. Photoluminescence (PL) spectroscopy is performed at room temperature to observe the SiNP PL. Whereas FGA is found to increase PL under certain conditions, i.e., annealing at high temperatures, increasing implantation fluence of H reduces the SiNP PL. Hydrogen implantation also introduces additional defect PL. After low-temperature annealing, the SiNP PL is found to improve, but the process is not found equivalently efficient as conventional FGA.
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| 18. |
- Darakchieva, Vanya
(author)
-
Infrared generalized ellipsometry on non-polar and superlattice group-III nitride films : Strain and phonon anisotropy
- 2008
-
In: Physica Status Solidi (A) Applications and Materials. - : Wiley. - 1862-6300. ; 205:4, s. 905-913
-
Journal article (peer-reviewed)abstract
- This contribution reviews the application of generalized infrared spectroscopic ellipsometry (GIRSE) to studies of optical phonons in heteroepitaxial wurtzite GaN films with a-plane orientation and c-plane Al(Ga)N/GaN superlattices. We demonstrate the capability of GIRSE to detect spectrally narrow dichroism, caused by anisotropic strain in non-polar oriented films thereby allowing a precise location of the phonon mode resonances for different polarizations. A distinct correlation between anisotropic strain components, which have been independently asessed by high-resolution X-ray diffraction, and phonon frequencies reveal the phonon deformation potentials. Further, GIRSF is shown to be a valuable tool in identification of superlattice phonon modes and their character. The frequency shifts of the superlattice modes with respect to the strain-free positions are analyzed versus strain and composition in order to assess the mode suitability for estimation of strain, polarization doping, and composition for the individual layers in complex device heterostructures. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA.
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| 19. |
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| 20. |
- Diplas, Spyros, et al.
(author)
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Materials for Energy Harvesting
- 2018
-
In: Physica Status Solidi (a) applications and materials science. - : WILEY-V C H VERLAG GMBH. - 1862-6300 .- 1862-6319. ; 215:17
-
Journal article (other academic/artistic)abstract
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| 21. |
- Dong, Wenjing, et al.
(author)
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Charge transport study of perovskite solar cells through constructing electron transport channels
- 2017
-
In: Physica Status Solidi (a) applications and materials science. - : Wiley-VCH Verlagsgesellschaft. - 1862-6300 .- 1862-6319. ; 214:10
-
Journal article (peer-reviewed)abstract
- Perovskite solar cells (PSC) have attracted much attention in the recent years. It is important to understand their working principle in order to uncover the reasons behind their high efficiency. In this study, the carrier transport mechanism of PSC by controlling the structure of a scaffold is investigated. CeO2 is used as an electron blocking material in PSCs to study the electron transport behavior for the first time. The influence of light absorption can be excluded because CeO2 has a similar bandgap to TiO2. A variety of scaffolds are constructed using nano-TiO2 and CeO2. The results show that electrons can transport from light absober (perovskite) to FTO electrode (external circuit) through two kinds of channels. The energy band level, as well as the electronic conductivity of the scaffolds, is are key issues that affect electron transport. Although perovskites are able to transport both electrons and holes, it is still necessary to have effective electron transport channels (ETCs) between perovskite and external circuit for the sake of high efficiency. Electrochemical impedance spectroscopy analysis suggests that the lack of such channels will result in high recombination. The number of ETCs and effecient electron-hole separation are also proven to be important for cell performance.
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| 22. |
- Englund, Sven, et al.
(author)
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Antimony-Doped Tin Oxide as Transparent Back Contact in Cu2ZnSnS4 Thin-Film Solar Cells
- 2019
-
In: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 216:22
-
Journal article (peer-reviewed)abstract
- Antimony-doped tin oxide (Sn2O3:Sb, ATO) is investigated as a transparent back contact for Cu2ZnSnS4 (CZTS) thin-film solar cells. The stability of the ATO under different anneal conditions and the effect from ATO on CZTS absorber growth are studied. It is found that ATO directly exposed to sulfurizing anneal atmosphere reacts with S, but when covered by CZTS, it does not deteriorate when annealed at T < 550 degrees C. The electrical properties of ATO are even found to improve when CZTS is annealed at T = 534 degrees C. At T = 580 degrees C, it is found that ATO reacts with S and degrades. Analysis shows repeatedly that ATO affects the absorber growth as large amounts of Sn-S secondary compounds are found on the absorber surfaces. Time-resolved anneal series show that these compounds form early during anneal and evaporate with time to leave pinholes behind. Device performance can be improved by addition of Na prior to annealing. The best CZTS device on ATO back contact herein has an efficiency of 2.6%. As compared with a reference on a Mo back contact, a similar open-circuit voltage and short-circuit current density are achieved, but a lower fill factor is measured.
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| 23. |
- Englund, Sven, et al.
(author)
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TiN Interlayers with Varied Thickness in Cu2ZnSnS(e)(4) Thin Film Solar Cells : Effect on Na Diffusion, Back Contact Stability, and Performance
- 2018
-
In: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 215:23
-
Journal article (peer-reviewed)abstract
- In this study, interlayers with varied thickness of TiN between Cu2ZnSnS(e)(4) (CZTS(e)) absorbers and Mo on soda-lime glass substrates are investigated for CZTS(e) thin film solar cells. Na diffusion is analyzed using Secondary Ion Mass Spectrometry and it is found that the use of thick TiN interlayers facilitates Na diffusion into the absorbers. The CZTS(e)/TiN/Mo interfaces are scrutinized using Transmission Electron Microscopy (TEM) Electron Energy Loss Spectroscopy (EELS). It is found that diffusion of chalcogens present in the precursor occurs through openings, resulting from surface roughness in the Mo, in the otherwise chemically stable TiN interlayers, forming point contacts of MoS(e)(2). It is further established that both chalcogens and Mo diffuse along the TiN interlayer grain boundaries. Solar cell performance for sulfur-annealed samples improved with increased thickness of TiN, and with a 200 nm TiN interlayer, the solar cell performance is comparable to a typical Mo reference. Pure TiN bulk contacts are investigated and shown to work, but the performance is still inferior to the TiN interlayer back contacts. The use of thick TiN interlayers offers a pathway to achieve high efficiency CZTS(e) solar cells on highly inert back contacts.
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| 24. |
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| 25. |
- Fujita, N., et al.
(author)
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Core reconstructions of the (100) edge dislocation in single crystal CVD diamond
- 2007
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In: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 204:7, s. 2211-2215
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Journal article (peer-reviewed)abstract
- Dislocations are common defects in both natural as well as in CVD-grown diamond. Recent advances in the growth of high quality single crystal CVD diamond have led to an increased interest in the atomistic and electronic structure of 100 dislocations. These dislocations are observed as mixed-type 45° and pure edge dislocations. Previously we investigated both types and found that the 45° is by far lower in core energy than the proposed structure of the edge type. In this work we focus on the straight 100 dislocation only and present novel core reconstructions. We find a minimum energy structure for the edge-type dislocation which has a similar core energy as the mixed-type dislocation.
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| 26. |
- Fujita, N, et al.
(author)
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Theoretical studies on 100 dislocations in single crystal CVD diamond
- 2006
-
In: Physica status solidi A. - Weinheim : Wiley-VCH Verlagsgesellschaft. - 1862-6300 .- 1862-6319. ; , s. 3070-3075
-
Conference paper (peer-reviewed)abstract
- Dislocations are common defects in both natural as well as in CVD-grown diamond. Recent advances in the growth of high quality single crystal CVD diamond have led to an increased interest in the atomistic and electronic structure of < 100 > dislocations. These dislocations are observed as mixed-type 45 degrees and pure edge dislocations. Hence in this work we present ab initio modelling studies on these two types of dislocations. The 45 degrees dislocation is found to be by far more stable than the pure edge and both dislocations lead to states in the electronic band gap. An alternative structure for the mixed-type dislocation, which is not straight but kinked and consists of short edge and screw segments, was found slightly higher in energy than the straight structure.
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| 27. |
- Gabrysch, Markus, et al.
(author)
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Compensation in boron-doped CVD diamond
- 2008
-
In: Physica status solidi. A, Applications and Materials Science. - : Wiley. - 1862-6300. ; 205:9, s. 2190-2194
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Journal article (peer-reviewed)abstract
- Hall-effect measurements on single crystal boron-doped CVD diamond in the temperature interval 80-450 K are presented together with SIMS measurements of the dopant concentration. Capacitance-voltage measurements on rectifying Schottky junctions manufactured on the boron-doped structures are also presented in this context. Evaluation of the compensating donor (N-D) and acceptor concentrations (N-A) show that in certain samples very low compensation ratios (N-D/N-A below 10(-4)) have been achieved. The influence of compensating donors on majority carrier transport and the significance for diamond device performance are briefly discussed.
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| 28. |
- Gallas, B., et al.
(author)
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Changes in optical properties of MnAs thin films on GaAs(001) induced by a- to B-phase transition
- 2008
-
In: Physica Status Solidi (a) applications and materials science. - : Wiley-VCH Verlagsgesellschaft. - 1862-6300 .- 1862-6319. ; 205:4, s. 859-862
-
Journal article (peer-reviewed)abstract
- MnAs layers with 45 nm thickness were grown epitaxially on GaAs(001) substrates. Ellipsometry measurements were made in the spectral range 0.045 eV to 6 eV as a function of temperature (between –10 °C and 50 °C) at 70° of incidence. In this way the transition from the hexagonal α-phase to the orthorhombic β-phase could be monitored. Non-zero off-diagonal elements of the Jones matrix for an azimuth of 38° off the [10] axis of the substrate indicate that the optical functions of MnAs are anisotropic in both phases. The optical conductivity exhibits low-energy interband transitions around 0.3 eV, more clearly seen in the α-phase than in the β-phase. Extrapolation of the optical conductivity to zero frequency confirms that the α-phase is about two times more conducting than the β-phase. A broad structure is observed in the visible range around 3 eV. The α-phase is characterised by an anisotropy induced energy difference of this structure with a maximum at 2.8 eV for the extraordinary index and at 3.15 eV for the ordinary index. This difference vanishes in the β-phase in which anisotropy mainly induces changes in amplitude of the 3 eV structure. The assignment of the structures will be discussed.
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| 29. |
- Gallas, B., et al.
(author)
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Monitoring the a to B-phase transition in MnAs/GaAs(001) thin films as funcion of temperature
- 2008
-
In: Physica Status Solidi (a) applications and materials science. - : Wiley-VCH Verlagsgesellschaft. - 1862-6300 .- 1862-6319. ; 205:4, s. 863-866
-
Journal article (peer-reviewed)abstract
- MnAs layers with a 5 nm thick amorphous GaAs capping layer were grown epitaxially on GaAs(001). Generalized ellipsometric measurements were made on a 45 nm thick layer in the spectral range 1.5–4 eV at temperatures between –10 °C and 50 °C in steps of 5 °C. By using both the diagonal and off-diagonal elements of the Jones matrix, the in-plane unixial anisotropy of MnAs was determined in terms of the ordinary and extraordinary complex dielectric functions. The measurements at each temperature could be well reproduced by modeling using the optical properties of the two limiting phases α-MnAs and β-MnAs determined at –10 °C and 50 °C, respectively. The best sensitivity to the volume fractions of the two phases was obtained near 2.2 eV by monitoring the generalized ellipsometric parameter Δp for which the variations reached 30°.
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| 30. |
- Gavagnin, Marco, et al.
(author)
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Magnetic force microscopy study of shape engineered FEBID iron nanostructures
- 2014
-
In: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 211:2, s. 368-374
-
Journal article (peer-reviewed)abstract
- The capability to control matter down to the nanoscale level in combination with the novel magnetic properties of nanomaterials have attracted increasing attention in the last few decades due to their applications in magnetic sensing, hard disc data storage and logic devices. Therefore, many efforts have been devoted to the implementation of both nanofabrication methods as well as characterization of magnetic nanoelements. In this study, Fe-based nanostructures have been synthesized on Si(100) by focused electron beam induced deposition (FEBID) utilizing iron pentacarbonyl as precursor. The so obtained nanostructures exhibit a remarkably high iron content (Fe>80at.%), expected to give rise to a ferromagnetic behaviour. For that reason, magnetic force microscopy (MFM) analyses were performed on the obtained FEBID Fe nanostructures. Moreover, object oriented micromagnetic framework (OOMMF) magnetic simulations have been executed to study the influence of the geometry on the magnetic properties of iron single-domain nanowires. FEBID is a mask-less nanofabrication method based on the injection of precursor gas molecules in proximity of the deposition area where their decomposition is locally induced by a focused electron beam.
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| 31. |
- Giannazzo, F., et al.
(author)
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Graphene integration with nitride semiconductors for high power and high frequency electronics
- 2017
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In: Physica Status Solidi (a) applications and materials science. - : WILEY-V C H VERLAG GMBH. - 1862-6300 .- 1862-6319. ; 214:4
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Journal article (peer-reviewed)abstract
- Group III nitride semiconductors (III-N), including GaN, AlN, InN, and their alloys, are currently the materials of choice for many applications in optoelectronics (light-emitting diodes, laser diodes), and high-power and high-frequency transistors. Due to its attractive electrical, optical, mechanical, and thermal properties, graphene (Gr) integration with III-N technology has been considered in the last few years, in order to address some of the major issues which still limit the performances of GaN-based devices. To date, most of the studies have been focused on the use of Gr as transparent conductive electrode (TCE) to improve current spreading from top electrodes and light extraction in GaN-LEDs. This paper will review recent works evaluating the benefits of Gr integration with III-N for high power and high frequency electronics. From the materials side, recent progresses in the growth of high quality GaN layers on Gr templates and in the deposition of Gr on III-N substrates and templates will be presented. From the applications side, strategies to use Gr for thermal management in high-power AlGaN/GaN transistors will be discussed. Finally, recent proposals of implementing new ultra-high-frequency (THz) transistors, such as the Gr base hot electron transistor (GBHET), by Gr integration with III-N will be highlighted. (C) 2016 WILEY-VCH Verlag GmbH amp; Co. KGaA, Weinheim
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| 32. |
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| 33. |
- Goto, Ken, et al.
(author)
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Study of Dislocations in Homoepitaxially and Heteroepitaxially Grown AlN Layers
- 2020
-
In: Physica Status Solidi (a) applications and materials science. - : WILEY-V C H VERLAG GMBH. - 1862-6300 .- 1862-6319. ; 217:24
-
Journal article (peer-reviewed)abstract
- Dislocation densities in AlN layers grown on c-plane sapphire and physical vapor transport-grown AlN (PVT-AlN) (0001) substrates, by metalorganic vapor phase epitaxy (MOVPE) and hydride vapor phase epitaxy (HVPE), respectively, are evaluated from the density of etch pits formed in sodium hydroxide (NaOH)/potassium hydroxide (KOH) eutectic heated to 450 degrees C. In the heteroepitaxial layers grown by MOVPE on the sapphire substrates, etch pits with different sizes are formed. Cross-sectional transmission electron microscopy (TEM) observations reveal that the large, medium, and small pits, with densities of 1.4 x 10(6), 2.6 x 10(7), and 6.9 x 10(9) cm(-2), respectively, correspond to screw, mixed, and edge dislocations, respectively. In contrast, in the homoepitaxial layers grown by HVPE on the PVT-AlN substrates, only one kind of etch pit with uniform size corresponding to the edge dislocations is formed with a density of 10(3)-10(4) cm(-2). Cross-sectional TEM observation confirms that the edge dislocations in the homoepitaxial layer propagate from the substrate through the interface, which indicates that the dislocation density does not increase during homoepitaxial growth by HVPE. The HVPE-AlN homoepitaxial layers grown on the PVT-AlN substrates are found to have very low dislocation density.
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| 34. |
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| 35. |
- Hammar, Mattias, 1961-, et al.
(author)
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Compound Semiconductors
- 2022
-
In: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 219:4
-
Journal article (other academic/artistic)
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| 36. |
- Haratizadeh, H, et al.
(author)
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Effects of Si doping position on the emission energy and recombination dynamics of GaN/AlGaN multiple quantum wells
- 2006
-
In: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 203:1, s. 149-153
-
Journal article (peer-reviewed)abstract
- We report results from detailed optical spectroscopy from MOCVD grown GaN/Al0.07Ga0.93N multiple quantum wells (MQWs). Effects of Si doping position on the emission energy and recombination dynamics were studied by means of photoluminescence (PL) and time-resolved PL measurements. The samples were Si doped with the same level but different position of the dopant layer. Only the sample doped in the well shows the MQW emission redshifted compare to the GaN bandgap. The redshift is attributed to the self-energy shift of the electron states due to the correlated motion of the electrons exposed to the fluctuating potential of the donor ions. At low temperature the PL decay time of the sample doped in the well by a factor of two is longer than for the barrier doped case. The difference is explained by the effect of interplay of free carriers and ions on the screening of the polarization field in these doped structures.
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| 37. |
- Hounsome, L.S., et al.
(author)
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Optical properties of vacancy related defects in diamond
- 2005
-
In: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 202:11, s. 2182-2187
-
Journal article (peer-reviewed)abstract
- ‹110› vacancy chains, multi-vacancy clusters and vacancy discs have been modeled using density functional theory within the AIMPRO and DFTB codes. While a connection can be established between the results on vacancy chains and previous EPR experiments, no connection can be made between the point defects and the optical properties of natural type IIa brown diamonds. However, a vacancy disc consisting of a {111} double plane of vacancies is stable and possesses an absorption spectrum similar to that found in brown diamonds.
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| 38. |
- Hult, Björn, 1993, et al.
(author)
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Investigation of Isolation Approaches and the Stoichiometry of SiN x Passivation Layers in “Buffer-Free” AlGaN/GaN Metal–Insulator–Semiconductor High-Electron-Mobility Transistors
- 2023
-
In: Physica Status Solidi (A) Applications and Materials Science. - : Wiley. - 1862-6319 .- 1862-6300. ; 220:8
-
Journal article (peer-reviewed)abstract
- Critical process modules for the fabrication of metal–insulator–semiconductor high-electron-mobility transistors (MISHEMTs) based on a novel ‘buffer-free’ AlGaN/GaN heterostructure grown with metal–organic chemical vapor deposition (MOCVD) are presented. The methods of isolation and passivation for this type of heterostructure are investigated. Utilizing nitrogen implantation, it is possible to achieve off-state destructive breakdown voltages (BVs) of 2496 V for gate–drain distances up to 25 μm, whereas mesa isolation techniques limit the BV below 1284 V. The stoichiometry of the SiNx passivation layer displays a small impact on the static and dynamic on-resistance. However, MISHEMTs with Si-rich passivation show off-state gate currents in the range of 1–100 μA mm−1 at voltages above 1000 V, which is reduced below 10 nA mm−1 using a stoichiometric SiNx passivation layer. Destructive BVs of 1532 and 1742 V can be achieved using gate-integrated and source-connected field plates for MIHEMTs with stoichiometric and Si–rich passivation layers, respectively. By decreasing the field plate lengths, it is possible to achieve BVs of 2200 V. This demonstrates the implementation of MISHEMTs with high-voltage operation and low leakage currents on a novel “buffer-free” heterostructure by optimizing the SiNx stoichiometry.
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| 39. |
- Hussain, Mushtaque, et al.
(author)
-
The improved piezoelectric properties of ZnO nanorods with oxygen plasma treatment on the single layer graphene coated polymer substrate
- 2014
-
In: Physica Status Solidi (a) applications and materials science. - : Wiley-VCH Verlag. - 1862-6300 .- 1862-6319. ; 211:2, s. 455-459
-
Journal article (peer-reviewed)abstract
- The step towards the fabrication of nanodevices with improved performance is of high demand; therefore, in this study, oxygen plasma treated ZnO nanorods based piezoelectric nanogenerator is developed on the single layer graphene coated PET flexible polymer substrate. ZnO nanorods on the single layer graphene are grown by hydrothermal growth method and the structural study is carried out by using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The piezoelectric properties of ZnO nanorods with and without plasma treatment were investigated by atomic force microscopy (AFM). The oxygen plasma treated sample of ZnO nanorods showed significant increase in the piezoelectric potential which could be due to the decrease in the defects levels in the ZnO and also increase in the mechanical properties of ZnO nanorods. Furthermore X-ray photoelectron spectroscopy (XPS) confirms that the filling of vacancies by oxygen in the matrix of ZnO using oxygen plasma treatment has gave an enhanced piezoelectric potential compared to the sample of ZnO nanorods not treated with oxygen plasma. In addition to XPS experiment, cathodoluminescence (CL) technique was used for the determination of defect level in the ZnO nanorods after the treatment of oxygen plasma and the obtained information supported the XPS data of oxygen plasma treatment sample by showing the decreased level of defect levels in the prepared sample. From the XPS and CL studies, it is observed that the defect level has significant influence on the piezoelectric potential of the ZnO nanostructures.
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| 40. |
- Iusan, Diana, et al.
(author)
-
Role of defects on the magnetic interactions in Mn-doped ZnO
- 2007
-
In: Physica status solidi. A, Applied research. - : Wiley. - 0031-8965 .- 1521-396X. ; 204:1, s. 53-60
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Journal article (peer-reviewed)abstract
- Oxide based diluted magnetic semiconductors are highly controversial from the point of view of intrinsic ferromagnetism brought in by doping with transition metal ions. By ab-initio Korringa-Kohn-Rostoker-Coherent-Potential-Approximation (KKR-CPA) calculations in the framework of density functional theory, we have obtained the electronic structure and magnetic exchange interaction parameters of Mn-doped ZnO in the presence and absence of several types of defects. A weak antiferromagnetic exchange interaction is observed in pure Mn-doped ZnO in the dilute limit with an increase in the strength of interactions with increasing concentration of Mn. In the presence of donor defects, such as oxygen vacancies and interstitial Zn, the interactions remain antiferromagnetic whereas in case of acceptor defects like Zn vacancies and N substitution of O, ferromagnetic interactions are observed. We have used the ab-initio exchange parameters in Monte-Carlo simulations for calculating finite temperature properties. Due to the short ranged behavior of interactions and disorder effects, the Curie temperatures calculated from Monte Carlo simulations show moderate values, not exceeding 50 K when the Mn content is 5%.
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| 41. |
- Jaafar, M., et al.
(author)
-
FePt thin film irradiated with high energy ions
- 2007
-
In: Physica status solidi. A, Applied research. - : Wiley. - 0031-8965 .- 1521-396X. ; 204:6, s. 1724-1730
-
Journal article (peer-reviewed)abstract
- The changes in structural and magnetic properties of FePt thin films due to the irradiation with high energy ions (Br7+ and Cl2+) were studied. From the hysteresis loops dominating in-plane anisotropy is derived, however, the samples present a minor out-of-plane component. The structure and the magnetic properties of the films can be tuned by selecting the appropriate irradiation parameters (different ions, energies and fluencies). For the irradiation parameters used in this study an in-plane anisotropy is favoured. Irradiation with Br7+ seems to induce minor changes in the structural ordering of the thin films, whereas the Cl2+ ions promote the amorphization of the surface of the films. In addition, a magnetic thin film pattemed at the micrometer scale was obtained after irradiation through a micrometric mask.
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| 42. |
- Jones, Robert, et al.
(author)
-
Electrical and optical properties of multivacancy centres in diamond
- 2007
-
In: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 204:9, s. 3059-3064
-
Journal article (peer-reviewed)abstract
- Recent experiments have shown that vacancy clusters are common defects in all types of monocrystalline brown diamond. This is believed to be due to an enhanced stability of the bounding (I 11) or (I 10) surfaces, arising from the formation of pi-bonded chains. These chains lead to broad bands of gap states with acceptor and donor levels around E-v + 2 eV. They also are likely to be responsible for the broad absorption continuum extending from the NIR through the visible and into the UV region which is characteristic of brown diamonds. High temperature treatment removes or transforms the clusters in CVD and type IIa diamonds leaving the diamond colourless. In type la brown diamonds, heat treatments up to 2500 degrees C lead to the breakup of the clusters and the formation of specific vacancy-nitrogen defects. We show that ab initio modelling of the interaction of nitrogen with the chains open a gap and leads to a threshold absorption energy in the 1-2 eV range. Finally, the calculations shed light on the identity of the vacancy-nitrogen defects observed.
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| 43. |
- Kakanakova-Georgieva, Anelia, et al.
(author)
-
Hot-wall MOCVD grown homoepitaxial GaN layers with intense intrinsic excitonic structure
- 2005
-
In: Phys. Stat. Sol. (a), Vol. 202. - : Wiley. ; , s. 739-743
-
Conference paper (peer-reviewed)abstract
- We report on a new approach to MOCVD growth of GaN, i.e. hot-wall MOCVD, and its application to homoepitaxy on GaN substrates. The quality of the epilayers is examined by photoluminescence (PL). Homoepitaxially hot-wall MOCVD grown GaN layers show (1) intense PL free-exciton emissions relative to the intensity of the principal bound-exciton emission and (2) homogeneous cathodoluminescence emission within the terraces developed during the step-flow growth. Impurity concentrations in the material are measured by secondary ion mass spectrometry (SIMS). (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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| 44. |
- Kataria, S., et al.
(author)
-
Chemical vapor deposited graphene : From synthesis to applications
- 2014
-
In: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 211:11, s. 2439-2449
-
Research review (peer-reviewed)abstract
- Graphene is a material with enormous potential for numerous applications. Therefore, significant efforts are dedicated to large-scale graphene production using a chemical vapor deposition (CVD) technique. In addition, research is directed at developing methods to incorporate graphene in established production technologies and process flows. In this paper, we present a brief review of available CVD methods for graphene synthesis. We also discuss scalable methods to transfer graphene onto desired substrates. Finally, we discuss potential applications that would benefit from a fully scaled, semiconductor technology compatible production process.
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| 45. |
- Keller, Jan, et al.
(author)
-
Atomic layer deposition of In2O3 transparent conductive oxide layers for application in Cu(In,Ga)Se2 solar cells with different buffer layers
- 2016
-
In: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 213:6, s. 1541-1552
-
Journal article (peer-reviewed)abstract
- This contribution presents the development of atomic layer deposited (ALD) In2O3 films for utilization as transparent conductive oxide (TCO) layers in Cu(In,Ga)Se2 (CIGSe) solar cells. The effects of ALD process parameters on the morphology and growth of In2O3 are studied and related to the electrical and optical properties of the films. Maintaining similar resistivity values compared to commonly used ZnO:Al (AZO) TCOs (ρ = (5–7) × 10−4 Ωcm), a superior mobility of μ ≈ 110 cm2/Vs could be achieved (more than five times higher than a ZnO:Al reference), which results in a significantly reduced parasitic optical absorption in the infrared region. Application of the optimized In2O3 layers in CIGSe solar cells with varying buffer layers (CdS and Zn1–xSnxOy (ZTO)) leads to a distinct improvement in short circuit current density Jsc in both cases. While for solar cells containing the ZTO/In2O3 window structure, a drop in open-circuit voltage Voc and a deterioration under illumination is observed, the TCO exchange (from AZO to In2O3) on CdS buffer layers results in an increase in Voc without detectable light bias degradation. The efficiency η of the best corresponding solar cells could be improved by about 1% absolute.
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| 46. |
- Keller, Jan, et al.
(author)
-
Effect of Cu content on post‐sulfurization of Cu(In,Ga)Se2 films and corresponding solar cell performance
- 2019
-
In: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 216:20
-
Journal article (peer-reviewed)abstract
- Herein, the effect of the initial copper content of co‐evaporated Cu(In1−x,Gax)Se2 (CIGS) absorber films on the impact of a post‐annealing step in elemental sulfur atmosphere is studied. The Cu concentration is varied over a wide range ([Cu]/[III] = CGI = 0.57–1.23), allowing to identify composition‐dependent trends in phase formation, chemical rearrangements, and solar cell performance after sulfurization. For all samples, a ternary CuInS2 layer forms at the surface. In addition, sulfur 1) is incorporated in randomly distributed CuIn(S,Se)2 mixed crystals underneath CuInS2; 2) diffuses into multidimensional defects (e.g., dislocations and grain boundaries); and 3) is bound in Na–In–S surface plates. It is found that Cu‐poor absorber composition (CGI ≤ 0.82) favors CuInS2 growth as compared with close‐stoichiometric CIGS films, driven by a faster diffusion of Cu toward the surface. For Cu‐rich absorbers (CGI > 1), Se—S exchange is significantly accelerated, presumably by the presence of Cu2−xSe phases reacting to Cu2−xS and eventually catalyzing CuInS2 formation. Finally, open‐circuit voltage (VOC), fill factor (FF), and efficiency (η) of corresponding solar cells increase after sulfurization with increasing CGI until stoichiometry is reached. The result is explained by a mitigated Cu depletion of the absorber bulk after sulfurization for close‐stoichiometric CIGS.
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| 47. |
- Khan, Azam, et al.
(author)
-
Analysis of direct and converse piezoelectric responses from zinc oxide nanowires grown on a conductive fabric
- 2015
-
In: Physica Status Solidi (a) applications and materials science. - : John Wiley & Sons. - 1862-6300 .- 1862-6319. ; 212:3, s. 579-584
-
Journal article (peer-reviewed)abstract
- Single crystalline hexagonal wurtzite zinc oxide nanowires were grown on conductive commercial textile fabric as piezoelectric material. Aqueous chemical growth (ACG) method was used for the synthesis of ZnO nanowires. Field emission surface scanning electron microscopy and X-ray diffraction techniques were used for surface and structural analysis of grown nanowires. The mechanical and piezoelectric properties of the nanowires were investigated by nanoindantation. Piezoelectric potentials up to 0.013 V were measured in response to direct applied loads in the range 0 - 11 mN. Also, a DC voltage was applied for measurement of converse piezoelectric response under a low constant applied force (~5 μN) and the piezoelectric coefficient was found to be 33.2 pm/V. This study performed on commercial conductive textile demonstrates the feasibility to fabricate wearable nanogenerator clothing.
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| 48. |
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| 49. |
- Khavari, Faraz, et al.
(author)
-
Comparison of Sulfur Incorporation into CuInSe(2)and CuGaSe(2)Thin-Film Solar Absorbers
- 2020
-
In: Physica Status Solidi (a) applications and materials science. - : WILEY-V C H VERLAG GMBH. - 1862-6300 .- 1862-6319. ; 217:22
-
Journal article (peer-reviewed)abstract
- Herein, sulfurization of CuInSe(2)and CuGaSe2(CGSe) absorber layers is compared to improve the understanding of sulfur incorporation into Cu(In,Ga)Se(2)films by annealing in a sulfur atmosphere. It is found for Cu-poor CuInSe(2)that for an annealing temperature of 430 degrees C, sulfur is incorporated into the surface of the absorber and forms an inhomogeneous CuIn(S,Se)(2)layer. In addition, at 530 degrees C, a surface layer of CuInS(2)is formed. In contrast, for Cu-poor CuGaSe(2)samples, S can only be introduced at 530 degrees C, mainly forming an alloy of CuGa(S,Se)(2), where no closed CuGaS(2)layer is found. In Cu-rich CuGaSe(2)samples, however, selenium is substituted by S already at 330 degrees C, which can be explained by a rapid phase transformation of Cu2 - xSe into Cu2 - x(S,Se). This transformation facilitates S in-diffusion and catalyzes CuGa(S,Se)(2)formation, likewise that previously reported to occur in CuInSe2. Finally, the Cu-poor CuInSe(2)solar cell performance is improved by the sulfurization step at 430 degrees C, whereas for the 530 degrees C sample, a decreasing fill factor and short-circuit current density are observed, indicating lower diffusion length accompanied by possible formation of an electron transport barrier. In contrast, the electrical characteristics deteriorate for all sulfurized Cu-poor CuGaSe(2)cells.
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| 50. |
- Khavari, Faraz, et al.
(author)
-
Post‐deposition sulfurization of CuInSe2 solar absorbers by employing sacrificial CuInS2 precursor layers
- 2022
-
In: Physica Status Solidi (a) applications and materials science. - : John Wiley & Sons. - 1862-6300 .- 1862-6319. ; 219:5
-
Journal article (peer-reviewed)abstract
- Herein, a new route of sulfur grading in CuInSe2 (CISe) thin-film solar absorbers by introducing an ultrathin (<50 nm) sacrificial sputtered CuInS2 (CIS) layer on top of the CISe. Different CIS top layer compositions (Cu-poor to Cu-rich) are analyzed, before and after a high-temperature treatment in selenium (Se)- or selenium+sulfur (SeS)-rich atmospheres. An [S]/([S] + [Se]) grading from the surface into the bulk of the Se- and SeS-treated samples is observed, and evidence of the formation of a mixed CuIn(S,Se)2 phase by Raman analysis and X-ray diffraction is provided. The optical bandgap from quantum efficiency measurements of solar cells is increased from 1.00 eV for the CISe reference to 1.14 and 1.30 eV for the Se- and SeS-treated bilayer samples, respectively. A ≈150 mV higher VOC is observed for the SeS-treated bilayer sample, but the cell exhibits blocking characteristics resulting in lower efficiency as compared with the CISe reference. This blocking is attributed to an internal electron barrier at the interface to the sulfur-rich surface layer. The difference in reaction routes and possible ways to improve the developed sulfurization process are discussed.
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