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1.	Ayedh, H. M., et al. (författare) Controlling the carbon vacancy in 4H-SiC by thermal processing 2018 Ingår i: ECS Transactions. - : Electrochemical Society Inc.. - 1938-6737 .- 1938-5862. ; , s. 91-97 Konferensbidrag (refereegranskat)abstract The carbon vacancy (Vc) is perhaps the most prominent point defect in silicon carbide (SiC) and it is an efficient charge carrier lifetime killer in high-purity epitaxial layers of 4H-SÌC. The Vc concentration needs to be controlled and minimized for optimum materials and device performance, and an approach based on post-growth thermal processing under C-rich ambient conditions is presented. It utilizes thermodynamic equilibration and after heat treatment at 1500 °C for 1 h, the Vc concentration is shown to be reduced by a factor-25 relative to that in as-grown state-of-the-art epi-layers. Concurrently, a considerable enhancement of the carrier lifetime occurs throughout the whole of >40 urn thick epi-layers.
2.	Berggren, Magnus, et al. (författare) Controlling inter-chain and intra-chain excitations of a poly(thiophene) derivative in thin films 1999 Ingår i: Chemical Physics Letters. - : Elsevier. - 0009-2614 .- 1873-4448. ; 304:1-2, s. 84-90 Tidskriftsartikel (refereegranskat)abstract The decay of photoexcitations in polythiophene chains has been studied in solid solutions of the polymer from room temperature to 4 K. A strong blue shift of the emission spectrum is observed in the polymer blend, as compared to the homopolymer. Dispersion of the polythiophene suppresses the non-radiative processes, which are suggested to be correlated to close contacts of polymer chains. Quantum chemistry modeling of the excited state distributed on two chains corroborate this conclusion.
3.	Bergman, Peder, et al. (författare) Defects in 4H silicon carbide 2001 Ingår i: Physica B, Vols. 308-310. ; , s. 675-679 Konferensbidrag (refereegranskat)abstract We present experimental results related to several different intrinsic defects that in different ways influence the material properties and are therefore technologically important defects. This includes the so-called D1 defect which is created after irradiation and which is temperature stable. From the optical measurements we were able to identify the D1 bound exciton as an isoelectronic defect bound at a hole attractive pseudo-donor, and we have been able to correlate this to the electrically observed hole trap HS1 seen in minority carrier transient spectroscopy (MCTS). Finally, we describe the formation and properties of a critical, generated defect in high power SiC bipolar devices. It is identified as a stacking fault in the SiC basal plane. It can be seen as a local reduction of the carrier lifetime, in triangular or rectangular shape, which explains the enhanced forward voltage drop in the diodes. The entire stacking faults are also optically active as can be seen as dark triangles and rectangles in low temperature cathodo-luminescence, and the fault and their bounding partial dislocations are seen and identified using synchrotron topography. © 2001 Elsevier Science B.V. All rights reserved.
4.	Bergman, Peder, 1961-, et al. (författare) Improved SiC Epitaxial Material for Bipolar Applications 2008 Ingår i: Proc. of MRS Spring Meeting 2008. ; , s. D05- Konferensbidrag (refereegranskat)abstract Epitaxial growth on Si-face nominally on-axis 4H-SiC substrates has been performed using horizontal Hot-wall chemical vapor deposition system. The formation of 3C inclusions is one of the main problem with growth on on-axis Si-face substrates. In situ surface preparation, starting growth parameters and growth temperature are found to play a vital role in the epilayer polytype stability. High quality epilayers with 100% 4H-SiC were obtained on full 2″ substrates. Different optical and structural techniques were used to characterize the material and to understand the growth mechanisms. It was found that the replication of the basal plane dislocation from the substrate into the epilayer can be eliminated through growth on on-axis substrates. Also, no other kind of structural defects were found in the grown epilayers. These layers have also been processed for simple PiN structures to observe any bipolar degradation. More than 70% of the diodes showed no forward voltage drift during 30 min operation at 100 A/cm2.
5.	Bergman, Peder, et al. (författare) Photoluminescence and electroluminescence characterization of InxGa1-x/InyGa1-yN multiple quantum well light emitting diodes 2002 Ingår i: Materials Science Forum, Vols. 389-393. ; , s. 1493-1496 Konferensbidrag (refereegranskat)abstract We report on a study of radiative recombination in In0.11Ga0.89N/In.0.01Ga0.99N multiple quantum wells (MQWs). The QWs were nominally undoped, while the InGaN barriers were Si doped. The MQW part is situated in the depletion field of a pn-junction structure with electrical contacts, so that both photoluminescence (PL) and electroluminescence (EL) can be studied as a function of bias. The PL and EL spectra are distinctly different, in particular at low temperatures. The spectral properties and related differences in PL decay times reflect different recombination conditions in the MQW region for the individual QWs.
6.	Bergman, Peder, et al. (författare) Radial Variation of Measured Carrier Lifetimes in Epitaxial Layers Grown with Wafer Rotation 2012 Ingår i: Materials Science Forum Vols 717 - 720. - : Trans Tech Publications Inc.. ; , s. 289-292 Konferensbidrag (refereegranskat)abstract In this report we present homoepitaxial growth of 4H-SiC on the Si-face of nominally on-axis substrates with diameter up to 100 mm in a hot-wall chemical vapor deposition reactor. A comparatively low carrier lifetime has been observed in these layers. Also, local variations in carrier lifetime are different from standard off-cut epilayers. The properties of layers were studied with more focus on charge carrier lifetime and its correlation with starting growth conditions, inhomogeneous surface morphology and different growth mechanisms.
7.	Bergman, Peder, 1961-, et al. (författare) Radiative recombination in InGaN/GaN multiple quantum well 2000 Ingår i: ICSCRM 99,1999. ; , s. 1571- Konferensbidrag (refereegranskat)
8.	Bergman, Peder, et al. (författare) The role of defects on optical and electrical properties of SiC 2000 Konferensbidrag (refereegranskat)abstract In this work we describe some of the defects in SiC observable using different optical characterisation techniques. This includes photoluminescence measurements to determine the presence of different defects. We also show that optical techniques can be developed for mapping characterisation, which are useful both for routine measurements and for determine spatial variations and presence of defects over larger areas. One such example is the lifetime mappings on epitaxial layers on entire wafers, which has shown the importance of structural defects replicated into the epitaxial layer. Optical measurements have also been correlated to structural measurements from X-ray topography to demonstrate the importance of the structural defects
9.	Booker, Ian Don, et al. (författare) Carrier Lifetime Controlling Defects Z(1/2) and RB1 in Standard and Chlorinated Chemistry Grown 4H-SiC 2014 Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 14:8, s. 4104-4110 Tidskriftsartikel (refereegranskat)abstract 4H-SiC epilayers grown by standard and chlorinated chemistry were analyzed for their minority carrier lifetime and deep level recombination centers using time-resolved photoluminescence (TRPL) and standard deep level transient spectroscopy (DLTS). Next to the well-known Z(1/2) deep level a second effective lifetime killer, RB1 (activation energy 1.05 eV, electron capture cross section 2 x 10(-16) cm(2), suggested hole capture cross section (5 +/- 2) x 10(-15) cm(2)), is detected in chloride chemistry grown epilayers. Junction-DLTS and bulk recombination simulations are used to confirm the lifetime killing properties of this level. The measured RB1 concentration appears to be a function of the iron-related Fe1 level concentration, which is unintentionally introduced via the corrosion of reactor steel parts by the chlorinated chemistry. Reactor design and the growth zone temperature profile are thought to enable the formation of RB1 in the presence of iron contamination under conditions otherwise optimal for growth of material with very low Z(1/2) concentrations. The RB1 defect is either an intrinsic defect similar to RD1/2 or EH5 or a complex involving iron. Control of these corrosion issues allows the growth of material at a high growth rate and with high minority carrier lifetime based on Z(1/2) as the only bulk recombination center.
10.	Booker, Ian Don, et al. (författare) Comparison of post-growth carrier lifetime improvement methods for 4H-SiC epilayers 2012 Ingår i: Silicon Carbide And Related Materials 2011, Pts 1 And 2. - : Trans Tech Publications Inc.. - 9783037854198 ; , s. 285-288, s. 285-288 Konferensbidrag (refereegranskat)abstract We compare two methods for post-growth improvement of bulk carrier lifetime in 4H-SiC: dry oxidations and implantations with either 12C or 14N, followed by high temperature anneals in Ar atmosphere. Application of these techniques to samples cut from the same wafer/epilayer yields 2- to 11-fold lifetime increases, with the implantation/annealing technique shown to give greater maximum lifetimes. The maximum lifetimes reached are ∼5 μs after 12C implantation at 600 °C and annealing in Ar for 180 minutes at 1500 °C. At higher annealing temperatures the lifetimes decreases, a result which differs from reports in the literature.
11.	Booker, Ian Don, et al. (författare) High-Resolution Time-Resolved Carrier Lifetime and Photoluminescence Mapping of 4H-SiC Epilayers 2012 Ingår i: Materials Science Forum Vols 717 - 720. - : Trans Tech Publications Inc.. ; , s. 293-296 Konferensbidrag (refereegranskat)abstract We present a comparison between time-resolved carrier lifetime mappings of several samples and integrated near band edge intensity photoluminescence mappings using a pulsed laser. High-injection conditions and as-grown material are used, which generally allow for the assumption of a single exponential decay. The photoluminescence intensity under these circumstances is proportional to the carrier lifetime and the mappings can be used to detect lifetime-influencing defects in epilayers and give an estimate of the carrier lifetime variation over the wafer. Several examples for the defect detection capability of the system are given.
12.	Booker, Ian Don, et al. (författare) Oxidation induced ON1, ON2a/b defects in 4H-SiC characterized by DLTS 2014 Ingår i: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2. - : Trans Tech Publications. ; , s. 281-284 Konferensbidrag (refereegranskat)abstract The deep levels ON1 and ON2a/b introduced by oxidation into 4H-SiC are characterized via standard DLTS and via filling pulse dependent DLTS measurements. Separation of the closely spaced ON2a/b defect is achieved by using a higher resolution correlation function (Gaver-Stehfest 4) and apparent energy level, apparent electron capture cross section and filling pulse measurement derived capture cross sections are given.
13.	Brosselard, P., et al. (författare) 3.3 kV-10A 4H-SiC PiN diodes 2009 Ingår i: Materials Science Forum, Vols. 600-603. - : Trans Tech Publ.. ; , s. 991-994 Konferensbidrag (refereegranskat)abstract An innovative process has been developed by Linköping University to prepare the 4HSiC substrate surface before epitaxial growth. The processed PiN diodes have been characterized in forward and reverse mode at different temperature. The larger diodes (2.56 mm2) have a very low leakage current around 20 nA @ 500V for temperatures up to 300°C. A performant yield (68%) was obtained on these larger diodes have a breakdown voltage superior to 500V. Electroluminescence characteristics have been done on these devices and they show that there is no generation of Stacking Faults during the bipolar conduction.
14.	Brosselard, P, et al. (författare) Comparison between 3.3kV 4H-SiC schottky and bipolar diodes 2008 Ingår i: IET Seminar Digest, Volume 2008, Issue 2, 2008. - : IEE. - 9788001041390 ; , s. 87-91 Konferensbidrag (refereegranskat)abstract Silicon Carbide Schottky and bipolar diodes have been fabricated with a breakdown voltage of 3.3kV. Diodes have been packaged and measured up to 300°C. The Schottky diode shows an increase of voltage drop with temperature and a reverse recovery charge independent from temperature. The PiN diode reverse recovery charge is ×20 at 300°C compared to that of the Schottky diode. 55% of the stressed bipolar diodes at 20A show a very small forward voltage drift. Theswitching losses of these stressed diodes are reduced by 20%. Substrate quality enhancement makes large SiC component fabrication possible (25mm 2 Schottky diodes) and bipolar components show very small tension drift with temperature.
15.	Brosselard, P, et al. (författare) High temperature behaviour of 3.5 kV 4H-SiC JBS diodes 2007 Ingår i: Proceedings of the International Symposium on Power Semiconductor Devices and ICs. ; , s. 285-288 Konferensbidrag (refereegranskat)abstract 4H-SiC JBS diodes have been manufactured on a Norstel epitaxied N/N + substrate using a JTE as edge termination. A breakdown voltage higherthan 3.5 kV has been measured on 0.16 and 2.56 mm 2 diodes. The leakage current in the 25°C-300°C temperature range depends on the bipolar/Schottky ratio whereas in forward mode its impact is minor. Diodes have been stressed in DC mode to show that the 2.56 mm 2 diodes have a slight forward voltage degradation independently of the layout. In switching mode, the recovery charge is only 20 nC for a 4A current switched at 300°C.
16.	Brosselard, P, et al. (författare) Low loss, large area 4.5 kV 4H-SiC PIN diodes with reduced forward voltage drift 2009 Ingår i: SEMICONDUCTOR SCIENCE AND TECHNOLOGY. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 24:9, s. 095004- Tidskriftsartikel (refereegranskat)abstract 4H-SiC PIN diodes have been fabricated on a Norstel P+/N/N+ substrate with a combination of Mesa and JTE as edge termination. A breakdown voltage of 4.5 kV has been measured at 1 mu A for devices with an active area of 2.6 mm(2). The differential on-resistance at 15 A (600 A cm(-2)) was of only 1.7 m Omega cm(2) (25 degrees C) and 1.9 m Omega cm(2) at 300 degrees C. The reduced recovery charge was of 300 nC for a switched current of 15 A (500 V) at 300 degrees C. 20% of the diodes showed no degradation at all after 60 h of dc stress (25-225 degrees C). Other 30% of the diodes exhibit a reduced voltage shift below 1 V. For those diodes, the leakage current remains unaffected after the dc stress. Electroluminescence investigations reveal a very low density of stacking faults after the dc stress. The manufacturing yield evidences the efficiency of the substrate surface preparation and our technological process.
17.	Brosselard, P., et al. (författare) The effect of the temperature on the bipolar degradation of 3.3 kV 4H-SiC PiN diodes 2008 Ingår i: 20th International Symposium on Power Semiconductor Devices ICs,2008. - Proceedings of the 20th International Symposium on Power Semiconductor Devices & ICs : Institute of Electrical and Electronics Engineers ( IEEE ). ; , s. 237- Konferensbidrag (refereegranskat)
18.	Buyanova, Irina, 1960-, et al. (författare) Mechanism for low-temperature photoluminescence in GaNAs/GaAs structures grown by molecular-beam epitaxy 1999 Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 75:4, s. 501- Tidskriftsartikel (refereegranskat)abstract The mechanism for low-temperature photoluminescence (PL) emissions in GaNAs epilayers and GaAs/GaNxAs1 - x quantum well (QW) structures grown by molecular-beam epitaxy is studied in detail, employing PL, PL excitation, and time-resolved PL spectroscopies. It is shown that even though quantum confinement causes a strong blueshift of the GaNAs PL emission, its major characteristic properties are identical in both QW structures and epilayers. Based on the analysis of the PL line shape, its dependence on the excitation power and measurement temperature, as well as transient data, the PL emission is concluded to be caused by a recombination of excitons trapped by potential fluctuations in GaNAs.
19.	Buyanova, Irina, 1960-, et al. (författare) Mechanism for radiative recombination in ZnCdO alloys 2007 Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90:26 Tidskriftsartikel (refereegranskat)abstract Temperature dependent cw- and time-resolved photoluminescence combined with absorption measurements are employed to evaluate the origin of radiative recombination in ZnCdO alloys grown by molecular-beam epitaxy. The near-band-edge emission is attributed to recombination of excitons localized within band tail states likely caused by nonuniformity in Cd distribution. Energy transfer between the tail states is argued to occur via tunneling of localized excitons. The transfer is shown to be facilitated by increasing Cd content due to a reduction of the exciton binding energy and, therefore, an increase of the exciton Bohr radius in the alloys with a high Cd content. © 2007 American Institute of Physics.
20.	Buyanova, Irina, 1960-, et al. (författare) Mechanism for rapid thermal annealing improvements in undoped GaNxAs1-x/GaAs structures grown by molecular beam epitaxy 2000 Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 77:15, s. 2325- Tidskriftsartikel (refereegranskat)abstract A systematic investigation of the effect of rapid thermal annealing (RTA) on optical properties of undoped GaNAs/GaAs structures is reported. Two effects are suggested to account for the observed dramatic improvement in the quality of the GaNxAs1-x/GaAs quantum structures after RTA: (i) improved composition uniformity of the GaNxAs1-x alloy, deduced from the photoluminescence (PL), PL excitation and time-resolved measurements; and (ii) significant reduction in the concentration of competing nonradiative defects, revealed by the optically detected magnetic resonance studies.
21.	Buyanova, Irina, 1960-, et al. (författare) Optical study of spin injection dynamics in InGaN/GaN quantum wells with GaMnN injection layers 2004 Ingår i: Journal of Vacuum Science & Technology B. - : American Vacuum Society. - 1071-1023 .- 1520-8567. ; 22:6, s. 2668-2672 Tidskriftsartikel (refereegranskat)abstract The spin injection dynamics of GaMnN/InGaN multiquantum well (MQW) light emitting diodes (LEDs) grown by molecular beam epitaxy were examined using picosecond-transient and circularly polarized photoluminescence (PL) measurements. Even with the presence of a room temperature ferromagnetic GaMnN spin injector, the LEDs are shown to exhibit very low efficiency of spin injection. Based on resonant optical orientation spectroscopy, the spin loss in the structures is shown to be largely due to fast spin relaxation within the InGaN MQW, which itself destroys any spin polarization generated by optical spin orientation or electrical spin injection. Typical photoluminescence decay times were 20-40 ns in both commercial GaN MQW LEDs with emission wavelengths between 420-470 nm and in the GaMnN/InGaN multi-quantum well MQW LEDs. In the wurtzite InGaN/GaN system, biaxial strain at the interfaces give rise to large piezoelectric fields directed along the growth axis. This built-in piezofield breaks the reflection symmetry of confining potential leading to the presence of a large Rashba term in the conduction band Hamiltonian which is responsible for the short spin relaxation times.
22.	Buyanova, Irina, 1960-, et al. (författare) Origin of near-band-edge emission in ZnCdO alloys 2007 Ingår i: 2007 MRS Fall Meeting,2007. ; , s. 319- Konferensbidrag (övrigt vetenskapligt/konstnärligt)
23.	Buyanova, Irina, 1960-, et al. (författare) Role of nitrogen in photoluminescence up-conversion in GaInNP/GaAs heterostructures 2007 Ingår i: AIP Conference Proceedings / Volume 893. - : American Institute of Physics (AIP). ; , s. 381-382 Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract Alloying of disordered GaInP with nitrogen is shown to lead to very efficient PLU in GaInNP/GaAs heterostructures grown by gas source molecular beam epitaxy (GS‐MBE). This is attributed to the N‐induced changes in the band alignment at the GaInNP/GaAs heterointerface from the type I for the N‐free structure to the type II in the samples with N compositions exceeding 0.5%. Based on the performed excitation power dependent measurements, a possible mechanism for the energy upconversion is suggested as being due to the two‐step two‐photon absorption. The photon recycling effect is shown to be important for the structures with N=1%, from time‐resolved PL measurements. © 2007 American Institute of Physics
24.	Buyanova, Irina, 1960-, et al. (författare) Time-resolved studies of photoluminescence in GaNxP1-x alloys : Evidence for indirect-direct band gap crossover 2002 Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 81:1, s. 52- Tidskriftsartikel (refereegranskat)abstract Time resolved photoluminescence spectroscopy is employed to monitor the effect of N incorporation on the band structure of GaNP alloys. Abrupt shortening in radiative lifetime of near-band gap emissions, arising from excitonic radiative recombination within N-related centers, is found to occur at very low N compositions of around 0.5%, i.e., within the same range as the appearance of the direct-band gap-like transitions in the photomodulated transmission spectra of GaNP reported previously. The effect has been attributed to an enhancement in oscillator strength of optical transitions due to band crossover from indirect to direct-band gap of the alloy.
25.	Carlsson, Fredrik, et al. (författare) Electroluminescence from implanted and epitaxially grown pn-diodes 2000 Ingår i: Materials Science Forum, Vols. 338-343. - : Trans Tech Publications Inc.. - 9780878498543 ; , s. 687-690 Konferensbidrag (refereegranskat)abstract The electroluminescence from pn-diodes with (1) aluminum doped epitaxially grown, (2) aluminum implanted or (3) aluminum and boron implanted p-layer have been investigated. The temperature dependence for both the spectra and the decays of the major spectral components have been investigated at temperatures from 80 K to 550 K. The implanted diodes show implantation damage in the form of the D-1 center and lack of emission from the aluminum center. The epitaxial diodes show luminescence from the aluminum center. The band edge luminescence is visible above 150 K for the epitaxial diode and above 300 K for the implanted. The emission from deep boron can be seen in the aluminum and boron co-implanted diode and in the epitaxially grown diode that have an unintentional boron doping below 10(17) cm(-3).
26.	Carlsson, F.H.C., et al. (författare) Electroluminescence from 4H-SiC Schottky Diodes 2001 Ingår i: Mat. Res. Soc. Symp. Proc., Vol. 640. ; , s. H4.8- Konferensbidrag (refereegranskat)
27.	Carlsson, Fredrik, et al. (författare) Neutron irradiation of 4H SiC 2001 Ingår i: Materials Science Forum, Vols. 353-356. ; , s. 555-558 Konferensbidrag (refereegranskat)abstract The effect of neutron irradiation on 4H SiC epitaxial layers are studied. Several different doses of both fast and thermal neutrons have been used and the samples have been annealed from 500 degreesC to 2000 degreesC. The defect concentration dependence on the fast neutron flux and on the annealing temperature is investigated. At temperatures from 900 degreesC to 1300 degreesC new lines between 3960 Angstrom and 4270 Angstrom appear. They are similar in behavior to the E-A and D1 spectra and are assumed to be related to excitons bound to isoelectronic centers. After annealing at 2000 degreesC another new line appears at 3809 Angstrom. The similarity of this line with phosphorus in 6H makes us tentatively ascribe it to phosphorus.
28.	Carlsson, Fredrik, et al. (författare) Trapped carrier electroluminescence (TraCE) - A novel method for correlating electrical and optical measurements 2001 Ingår i: Physica B, Vols. 308-310. ; , s. 1165-1168 Konferensbidrag (refereegranskat)abstract SiC is a semiconductor with very good material properties for high power, high frequency and high temperature applications. During device fabrication irradiation with particles is often used, e.g., ion-implantation, which creates intrinsic defects. The most persistent defect in SiC is DI that appears after irradiation and subsequent high temperature annealing. A direct method called Trapped Carrier Electroluminescence (TraCE) for correlating minority carrier traps with luminescence measurements is presented. A semi-transparent Schottky diode under reverse bias is illuminated with a laser pulse of above band gap light to create minority carriers that are captured to traps in the space charge region. Majority carriers are introduced when the reverse bias is removed and the space charge region is reduced. The majority carriers recombine with the trapped minority carriers and the emitted light from the recombination is detected. TraCE has been used to study and correlate the DI bound exciton luminescence from intrinsic defects in SiC with an electrically observed hole trap HS1. © 2001 Elsevier Science B.V. All rights reserved.
29.	Choubina, Tatiana, 1950-, et al. (författare) Light diffusion in GaN epilayers 2007 Ingår i: 3rd International Conference on Spontaneous Coherence in Excitonic System,2007. Konferensbidrag (övrigt vetenskapligt/konstnärligt)
30.	Choubina, Tatiana, 1950-, et al. (författare) Realization of slow light in GaN crystals 2008 Ingår i: IWN 2008,2008. Konferensbidrag (refereegranskat)
31.	Choubina, Tatiana, 1950-, et al. (författare) Slow light in GaN 2008 Ingår i: 16th Int. Symp. ¿Nanostructures: Physics and Technology,2008. ; , s. 257- Konferensbidrag (refereegranskat)
32.	Choubina, Tatiana, 1950-, et al. (författare) The slow light in GaN 2008 Ingår i: ICPS2008,2008. ; , s. 647- Konferensbidrag (refereegranskat)
33.	Domeij, Martin, et al. (författare) Dynamic avalanche and trapped charge in 4H-SiC diodes 2000 Ingår i: SILICON CARBIDE AND RELATED MATERIALS. ; , s. 1327-1330, s. 1327-1330 Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract A dynamically reduced breakdown voltage from more than 2 kV under static conditions to 300 V during reverse recovery was measured for 4H-SiC p(+)nn(+) diodes. Device simulation indicates that deep hole-trapping donors in the n-base, close the pn junction, could explain the dynamically reduced breakdown voltage. Hole traps situated 0.66 eV above the valence band were found in the diode n-base by DLTS measurements.
34.	Egilsson, T, et al. (författare) Exciton and defect photoluminescence from SiC 2003 Ingår i: Silicon carbide and related materials 2002. - 0878499202 - 9780878499205 ; , s. 81-120 Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract Wide-bandgap semiconductors such as SiC, III-V nitrides and related compounds are attracting rapidly increasing attention due to their other, very interesting, physical properties which are often superior in many ways to those of conventional semiconductors. Steady improvements in crystal quality, and improved knowledge concerning their physical properties, are leading to rapid developments in high-power, high-temperature, high-frequency electronics and blue-light emitters. This book comprises the proceedings of the fourth European Conference on Silicon Carbide and Related Materials, held on the 1 to 5 September 2002 in Link3œping, Sweden. This conference series continued its tradition of being the main forum for presenting results, and discussing progress, among university and industry researchers who are active in the fields of SiC and related materials. These proceedings therefore document the latest experimental and theoretical understanding of the growth of bulk and epitaxial layers, the properties of the resultant material, the development of suitable processes and of electronic devices that can exploit and benefit best from the outstanding physical properties offered by wide-bandgap materials
35.	Ejebjörk, Niclas, 1984, et al. (författare) Optimization of SiC MESFET for high power and high frequency applications 2011 Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 1662-9752 .- 0255-5476. ; 679-680, s. 629-632, s. 629-632 Konferensbidrag (refereegranskat)abstract SiC MESFETs were scaled both laterally and vertically to optimize high frequency and high power performance. Two types of epi-stacks of SiC MESFETs were fabricated and measured. The first type has a doping of 3×10^17 cm-3 in the channel and the second type has higher doping (5×10^17 cm-3) in the channel. The higher doping allows the channel to be thinner for the same current density and therefore a reduction of the aspect ratio is possible. This could impede short channel effects. For the material with higher channel doping the maximum transconductance is 58 mS/mm. The maximum current gain frequency, fT, and maximum frequency of oscillation, fmax, is 9.8 GHz and 23.9 GHz, and 12.4 GHz and 28.2 GHz for the MESFET with lower doped channel and higher doping, respectively.
36.	Ellison, A, et al. (författare) Fast SiC epitaxial growth in a chimney CVD reactor and HTCVD crystal growth developments 2000 Ingår i: Materials science Forum, Vols. 338-342. - : Trans Tech Publications Inc.. - 0878498540 ; , s. 131-136 Konferensbidrag (refereegranskat)abstract The epitaxial growth of SiC is investigated in a CVD process based on a vertical hot-wall, or "chimney", reactor geometry. Carried out at increased temperatures (1650 to 1850 degreesC) and concentrations of reactants, the growth process enables epitaxial rates ranging from 10 to 50 mum/h. The growth rate is shown to be influenced by two competing processes: the supply of growth species in the presence of homogeneous gas-phase nucleation, and, the etching effect of the hydrogen carrier gas. The quality of thick (20 to 100 mum) low-doped 4H-SiC epitaxial layers grown at rates ranging between 10 and 25 mum/h are discussed in terms of thickness uniformity, surface morphology and purity. The feasibility of high voltage Schottky rectifiers (V-BR from 2 to similar to3.8 kV) on as-grown chimney CVD epilayers is reported. In a second part, recent developments of the High Temperature Chemical Vapor Deposition (HTCVD) technique for SiC crystal growth are described. Using pure gases (SiH4 and C2H4) as source material and growth temperatures of 2100-2300 degreesC, this technique enables at present growth rates ranging from 0.4 to 0.8 mm/h. 6H and 4H-SiC crystals of thickness up to 7 mm and diameters up to 40 mm have been grown. We report micropipe densities of similar to 80 cm(-2) over areas of 0.5 cm(2) in 35 mm diameter 4H-SiC wafers sliced from HTCVD grown crystals. Undoped wafer demonstrators exhibit semi-insulating behavior with a bulk resistivity higher than 7.10(9) Omega cm at room temperature.
37.	Ellison, A, et al. (författare) SiC crystal growth by HTCVD 2004 Ingår i: Materials Science Forum, Vols. 457-460. ; , s. 9- Konferensbidrag (refereegranskat)abstract Advances in the development of the HTCVD technique for growth of bulk 2-inch diameter 4H SiC crystals are reviewed with demonstration of micropipe density down to 0.3 cm(-2), low crystal bending and X-ray rocking curve widths of 12". High Al doping in p-type substrates enables resistivities down to 0.5 Omega cm without increased micropipe density, while too high N doping causes spontaneous stacking faults formation in annealed n-type substrates. High purity semi-insulating wafers, grown under conditions reducing the incorporation of Si-vacancies, exhibit lower density of vacancy clusters and better properties for microwave device applications.
38.	Eriksson, Martin. O., et al. (författare) The Dynamics of Charged and Neutral Excitons in an InGaN Quantum Dot on a GaN Pyramid Annan publikation (övrigt vetenskapligt/konstnärligt)abstract The neutral (X0) and negatively charged excitons (X-) in an InGaN QD on a GaN pyramid is studied by the timeintegrated micro-photoluminescence (μPL) and time-resolved micro-photoluminescence (TRμPL) microcopies. Both X0 and X- exhibit mono-exponential decay curves with fitted lifetimes of 310 and 140 ps, respectively. Neither energy shifts nor changes in the life times X0 and X- with increasing excitation power were observed, indicating the QD is small and free from the quantum confine Stark effect. The TRμPL is not only a powerful technique for studying the dynamics of exciton in QDXs, but also for the identification of exciton complexes in QDs.
39.	Eriksson, Martin (författare) Photoluminescence Characteristics of III-Nitride Quantum Dots and Films 2017 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract III-Nitride semiconductors are very promising in both electronics and optical devices. The ability of the III-Nitride semiconductors as light emitters to span the electromagnetic spectrum from deep ultraviolet light, through the entire visible region, and into the infrared part of the spectrum, is a very important feature, making this material very important in the field of light emitting devices. In fact, the blue emission from Indium Gallium Nitride (InGaN), which was awarded the 2014 Nobel Prize in Physics, is the basis of the common and important white light emitting diode (LED).Quantum dots (QDs) have properties that make them very interesting for light emitting devices for a range of different applications, such as the possibility of increasing device efficiency. The spectrally well-defined emission from QDs also allows accurate color reproduction and high-performance communication devices. The small size of QDs, combined with selective area growth allows for an improved display resolution. By control of the polarization direction of QDs, they can be used in more efficient displays as well as in traditional communication devices. The possibility of sending out entangled photon pairs is another QD property of importance for quantum key distribution used for secure communication.QDs can hold different exciton complexes, such as the neutral single exciton, consisting of one electron and one hole, and the biexciton, consisting of two excitons. The integrated PL intensity of the biexciton exhibits a quadratic dependence with respect to the excitation power, as compared to the linear power dependence of the neutral single exciton. The lifetime of the neutral exciton is 880 ps, whereas the biexciton, consisting of twice the number of charge carriers and lacks a dark state, has a considerably shorter lifetime of only 500 ps. The ratio of the lifetimes is an indication that the size of the QD is in the order of the exciton Bohr radius of the InGaN crystal making up these QDs in the InGaN QW.A large part of the studies of this thesis has been focused on InGaN QDs on top of hexagonal Gallium Nitride (GaN) pyramids, selectively grown by Metal Organic Chemical Vapor Deposition (MOCVD). On top of the GaN pyramids, an InGaN layer and a GaN capping layer were grown. From structural and optical investigations, InGaN QDs have been characterized as growing on (0001) facets on truncated GaN pyramids. These QDs exhibit both narrow photoluminescence linewidths and are linearly polarized in directions following the symmetry of the pyramids.In this work, the neutral single exciton, and the more rare negatively charged exciton, have been investigated. At low excitation power, the integrated intensity of the PL peak of the neutral exciton increases linearly with the excitation power. The negatively charged exciton, on the other hand, exhibits a quadratic power dependence, just like that of the biexciton. Upon increasing the temperature, the power dependence of the negatively charged exciton changes to linear, just like the neutral exciton. This change in power dependence is explained in terms of electrons in potential traps close to the QD escaping by thermal excitation, leading to a surplus of electrons in the vicinity of the QD. Consequently, only a single exciton needs to be created by photoexcitation in order to form a negatively charged exciton, while the extra electron is supplied to the QD by thermal excitation.Upon a close inspection of the PL of the neutral exciton, a splitting of the peak of just below 0.4 meV is revealed. There is an observed competition in the integrated intensity between these two peaks, similar to that between an exciton and a biexciton. The high energy peak of this split exciton emission is explained in terms of a remotely charged exciton. This exciton state consists of a neutral single exciton in the QD with an extra electron or hole in close vicinity of the QD, which screens the built-in field in the QD.The InGaN QDs are very small; estimated to be on the order of the exciton Bohr radius of the InGaN crystal, or even smaller. The lifetimes of the neutral exciton and the negatively charged exciton are approximately 320 ps and 130 ps, respectively. The ratio of the lifetimes supports the claim of the QD size being on the order of the exciton Bohr radius or smaller, as is further supported by power dependence results. Under the assumption of a spherical QD, theoretical calculations predict an emission energy shift of 0.7 meV, for a peak at 3.09 eV, due to the built-in field for a QD with a diameter of 1.3 nm, in agreement with the experimental observations.Studying the InGaN QD PL from neutral and charged excitons at elevated temperatures (4 K to 166 K) has revealed that the QDs are surrounded by potential fluctuations that trap charge carriers with an energy of around 20 meV, to be compared with the exciton trapping energy in the QDs of approximately 50 meV. The confinement of electrons close to the QD is predicted to be smaller than for holes, which accounts for the negative charge of the charged exciton, and for the higher probability of capturing free electrons. We have estimated the lifetimes of free electrons and holes in the GaN barrier to be 45 ps and 60 ps, in consistence with excitons forming quickly in the barrier upon photoexcitation and that free electrons and holes get trapped quickly in local potential traps close to the QDs. This analysis also indicates that there is a probability of 35 % to have an electron in the QD between the photoexcitation pulses, in agreement with a lower than quadratic power dependence of the negatively charged exciton.InN is an attractive material due to its infrared emission, for applications such as light emitters for communication purposes, but it is more difficult to grow with high quality and low doping concentration as compared to GaN. QDs with a higher In-composition or even pure InN is an interesting prospect as being a route towards increased quantum confinement and room temperature device operation. For all optical devices, p-type doping is needed. Even nominally undoped InN samples tend to be heavily n-type doped, causing problems to make pn-junctions as needed for LEDs. In our work, we present Mg-doped p-type InN films, which when further increasing the Mg-concentration revert to n-type conductivity. We have focused on the effect of the Mg-doping on the light emission properties of these films. The low Mg doped InN film is inhomogeneous and is observed to contain areas with n-type conductivity, so called n-type pockets in the otherwise p-type InN film. A higher concentration of Mg results in a higher crystalline quality and the disappearance of the n-type pockets. The high crystalline quality has enabled us to determine the binding energy of the Mg dopants to 64 meV. Upon further increase of the Mg concentration, the film reverts to ntype conductivity. The highly Mg doped sample also exhibits a red-shifted emission with features that are interpreted as originating from Zinc-Blende inclusions in the Wurtzite InN crystal, acting as quantum wells. The Mg doping is an important factor in controlling the conductivity of InN, as well as its light emission properties, and ultimately construct InN-based devices.In summary, in this thesis, both pyramidal InGaN QDs and InGaN QDs in a QW have been investigated. Novel discoveries of exciton complexes in these QD systems have been reported. Knowledge has also been gained about the challenging material InN, including a study of the effect of the Mg-doping concentration on the semiconductor crystalline quality and its light emission properties. The outcome of this thesis enriches the knowledge of the III-Nitride semiconductor community, with the long-term objective to improve the device performance of III-Nitride based light emitting devices.
40.	Esmaeili, M., et al. (författare) Photoluminescence study of MOCVD-grown GaN/AlGaN MQW nanostructures : Influence of Al composition and Si doping 2007 Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 18:2 Tidskriftsartikel (refereegranskat)abstract A detailed study of low-temperature photoluminescence (PL) in GaN/AlGaN multiple quantum well (MQW) nanostructures has been reported. We have investigated the effect of Si doping and Al content on PL spectra and PL decay time of these structures. The temperature dependence of radiative as well as non-radiative lifetimes have been evaluated between 2K and room temperature for different Si doping. We found that radiative recombination at higher temperatures even up to RT is stronger in the doped sample, compared to the undoped one. Hole localization in GaN/AlGaN MQWs with different compositions of Al is demonstrated via PL transient decay times and LO phonon coupling. It is found that there is an increasing of the decay time at the PL peak emission with increasing Al composition. For the undoped sample, a non-exponential PL decay behaviour at 2K is attributed to localized exciton recombination. A slight upshift in QWs PL peak with increasing Al composition is observed, which is counteracted by the expected rise of the internal QW electric field with increasing Al. The localization energies have been evaluated by studying the variation of the QW emission versus temperature and we found out that the localization energy increases with increasing Al composition. © IOP Publishing Ltd.
41.	Fagerlind, Martin, et al. (författare) Influence of Large-Aspect-Ratio Surface Roughness on Electrical Characteristics of AlGaN/AlN/GaN HFETs 2012 Ingår i: IEEE transactions on device and materials reliability. - : Institute of Electrical and Electronics Engineers (IEEE). - 1530-4388 .- 1558-2574. ; 12:3, s. 538-546 Tidskriftsartikel (refereegranskat)abstract The effect of large-aspect-ratio surface roughness of AlGaN/GaN wafers is investigated. The roughness has a surface morphology consisting of hexagonal peaks with maximum peak-to-valley height of more than 100 nm and lateral peak-to-peak distance between 25 and 100 mu m. Two epitaxial wafers grown at the same time on SiC substrates having different surface orientation and with a resulting difference in AlGaN surface roughness are investigated. Almost no difference is seen in the electrical characteristics of the materials, and the electrical uniformity of the rough material is comparable to that of the smoother material. The reliability of heterostructure field-effect transistors from both materials have been tested by stressing devices for up to 100 h without any significant degradation. No critical effect, from the surface roughness, on device fabrication is experienced, with the exception that the roughness will directly interfere with step-height measurements.
42.	Ghezellou, Misagh, 1988-, et al. (författare) The role of boron related defects in limiting charge carrier lifetime in 4H–SiC epitaxial layers 2023 Ingår i: APL Materials. - : American Institute of Physics (AIP). - 2166-532X. ; 11:3 Tidskriftsartikel (refereegranskat)abstract One of the main challenges in realizing 4H–SiC (silicon carbide)-based bipolar devices is the improvement of minority carrier lifetime in as-grown epitaxial layers. Although Z1/2 has been identified as the dominant carrier lifetime limiting defect, we report on B-related centers being another dominant source of recombination and acting as lifetime limiting defects in 4H–SiC epitaxial layers. Combining time-resolved photoluminescence (TRPL) measurement in near band edge emission and 530 nm, deep level transient spectroscopy, and minority carrier transient spectroscopy (MCTS), it was found that B related deep levels in the lower half of the bandgap are responsible for killing the minority carriers in n-type, 4H–SiC epitaxial layers when the concentration of Z1/2 is already low. The impact of these centers on the charge carrier dynamics is investigated by correlating the MCTS results with temperature-dependent TRPL decay measurements. It is shown that the influence of shallow B acceptors on the minority carrier lifetime becomes neutralized at temperatures above ∼422 K. Instead, the deep B related acceptor level, known as the D-center, remains active until temperatures above ∼570 K. Moreover, a correlation between the deep level concentrations, minority carrier lifetimes, and growth parameters indicates that intentional nitrogen doping hinders the formation of deep B acceptor levels. Furthermore, tuning growth parameters, including growth temperature and C/Si ratio, is shown to be crucial for improving the minority carrier lifetime in as-grown 4H–SiC epitaxial layers.
43.	Godlewski, M, et al. (författare) Compensation mechanisms in magnesium doped GaN 2004 Ingår i: Physica status solidi. A, Applied research. - : Wiley. - 0031-8965 .- 1521-396X. ; 201:2, s. 216-220 Tidskriftsartikel (refereegranskat)abstract Compensation processes in magnesium doped GaN epilayers and bulk samples are studied. We demonstrate enhancement of potential fluctuations in Mg doped samples, from Kelvin probe atomic force microscopy measurements. Large- and small-scale light emission fluctuations are also demonstrated. Micro-photoluminescence (PL) study indicates an unusual anti-correlation between the intensities of excitonic and defect-related emission processes in p-type doped structures and also the presence of the so-called hot-PL. Hot-PL observed in compensated p-type samples, we relate to the presence of strong potential fluctuations. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
44.	Godlewski, M, et al. (författare) Influence of structural properties and of growth conditions on exciton properties in ZnCdSe/ZnSe quantum well structures 2002 Ingår i: Materials Science Forum, Vols. 389-393. ; , s. 63-66 Konferensbidrag (refereegranskat)abstract Structural and optical properties of relaxed and pseudomorphic ZnCdSe/ZnSe quantum well heterostructures are described. Structural quality and strain conditions of the films are linked with their light emission properties. From the temperature dependence of photoluminescence (PL) spectra we estimate exciton coupling constants to acoustic phonons in pseudomorphic and relaxed structures. The coupling is noticeably weaker in strain-relaxed structures with strong localization effects. PL kinetic studies confirm strong localization of excitons in strain-relaxed structures.
45.	Godlewski, M, et al. (författare) Interaction of microwave heated hot carriers with recombination centers 2002 Ingår i: Materials Science Forum, Vols. 389-393. ; , s. 19-26 Konferensbidrag (refereegranskat)abstract We describe application of the technique of optically detected cyclotron resonance (ODCR) to the studies of exciton properties in quantum well structures of CdTe/CdMnTe in the limit of strong localization effects. Microwave-heated free carriers, at cyclotron resonance conditions, can site- or impurity-delocalise excitons, resulting in a strong modification of a low temperature photoluminescence. In consequence, the ODCR allows to study processes of carrier/exciton localization. We show that localization effects are very strong in quantum well structures of CdTe/CdMnTe with large Mn fractions in the CdMnTe barriers.
46.	Godlewski, M, et al. (författare) Mechanism of intra-shell recombination of transition metal and rare earth ions in nanostructures of II-VI compounds 2004 Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 380:01-Feb, s. 45-49 Tidskriftsartikel (refereegranskat)abstract Based on the results of optically detected magnetic resonance (ODMR) and time-resolved investigations we relate the observed lifetime shortening of intra-shell Mn2+ emission to spin dependent magnetic interactions between localized spins of Mn2+ ions and spins/magnetic moments of free carriers. We show that this mechanism is active both in bulk and in low dimensional structures, such as quantum wells (QWs), quantum dots (QDs) and nanostructures. (C) 2004 Elsevier B.V. All rights reserved.
47.	Godlewski, M., et al. (författare) Mechanism of radiative recombination in acceptor-doped bulk GaN crystals 1999 Ingår i: 20th International Conference on Defects in Semiconductors ICDS-20,1999. - Physica B, Vol. 273-274 : Elsevier. ; , s. 39- Konferensbidrag (refereegranskat)abstract Optical and electrical properties of acceptor-doped bulk GaN crystals are discussed. Though introducing Zn and Ca to bulk GaN does not significantly change electron concentration, it results in the appearance of a blue photoluminescence band accompanying the relatively strong yellow band usually present. Highly resistive GaN : Mg crystals are obtained when high amount of Mg is introduced to the Ga melt during high-pressure synthesis. Change of electrical properties of Mg-doped bulk crystals is accompanied by the appearance of a strong blue emission of GaN similar to that in Ca- and Zn-doped crystals. Optically detected magnetic resonance investigations indicate a multi-band character of this blue emission and suggest possible mechanism of compensation in acceptor-doped bulk GaN.
48.	Godlewski, M., et al. (författare) Mn2+ intra-shell recombination in bulk and quantum dots of II-VI compounds 2002 Ingår i: Journal of Alloys and Compounds. - 0925-8388 .- 1873-4669. ; 341:1-2 Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract Origin of a fast component of the photoluminescence (PL) decay of Mn 2+ intra-shell 4T1 ? 6A 1 transition in bulk and quantum dot structures is discussed based on the results of PL, PL kinetics and optically detected magnetic resonance experiments. It is demonstrated that a fast component of the PL decay, reported previously for quantum dot structure and related to quantum confinement effects, is also observed in bulk samples and is very much enhanced upon generation of free carriers. The appearance of this fast component of the PL decay is related to a very efficient spin cross-relaxation between localized spins of Mn ions and spins of free carriers. © 2002 Elsevier Science B.V. All rights reserved.
49.	Godlewski, M., et al. (författare) Photoluminescence mechanisms in undoped and in Mg doped bulk GaN 1999 Ingår i: 24th International Conference on the Physics of Semiconductors,1998. - Proc. of the 24th International Conference on the Physics of Semiconductors, ed. by D. Gershoni : World Scientific, Singapore. ; , s. IX B17- Konferensbidrag (övrigt vetenskapligt/konstnärligt)
50.	Godlewski, M., et al. (författare) Quasi-zero-dimensional excitons in quantum well structures of CdTe/CdMnTe 2000 Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 214, s. 420-423 Tidskriftsartikel (refereegranskat)abstract In this work we discuss properties of excitons in quantum well structures of CdTe/CdMnTe. We analyse exciton-phonon interaction of strongly localised excitons by studying the temperature dependence of photoluminescence (PL) (width and spectral position of PL lines) and PL dynamics. Evidence of a slow exciton migration/tunnelling among localised sites is presented and its effect on the luminescence spectrum and exciton dynamics is discussed. We show that strong localisation of excitons, observed at low temperatures, results in quasi-zero-dimensional nature of excitons.

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