| 1. |
- Azarov, Alexander, et al.
(författare)
-
Optical activity and defect/dopant evolution in ZnO implanted with Er
- 2015
-
Ingår i: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 118:12
-
Tidskriftsartikel (refereegranskat)abstract
- The effects of annealing on the optical properties and defect/dopant evolution in wurtzite (0001) ZnO single crystals implanted with Er ions are studied using a combination of Rutherford backscattering/channeling spectrometry and photoluminescence measurements. The results suggest a lattice recovery behavior dependent on ion dose and involving formation/evolution of an anomalous multipeak defect distribution, thermal stability of optically active Er complexes, and Er outdiffusion. An intermediate defect band occurring between the surface and ion-induced defects in the bulk is stable up to 900 degrees C and has a photoluminescence signature around 420 nm well corresponding to Zn interstitials. The optical activity of the Er atoms reaches a maximum after annealing at 700 degrees C but is not directly associated to the ideal Zn site configuration, since the Er substitutional fraction is maximal already in the as-implanted state. In its turn, annealing at temperatures above 700 degrees C leads to dissociation of the optically active Er complexes with subsequent outdiffusion of Er accompanied by the efficient lattice recovery.
|
|
| 2. |
- Badel, Xavier, et al.
(författare)
-
Improvement of an X-ray imaging detector based on a scintillating guides screen
- 2002
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 487:1-2, s. 129-135
-
Tidskriftsartikel (refereegranskat)abstract
- An X-ray imaging detector has been developed for dental applications. The principle of this detector is based on application of a silicon charge coupled device covered by a scintillating wave-guide screen. Previous studies of such a detector showed promising results concerning the spatial resolution but low performance in terms of signal to noise ratio (SNR) and sensitivity. Recent results confirm the wave-guiding properties of the matrix and show improvement of the detector in terms of response uniformity, sensitivity and SNR. The present study is focussed on the fabrication of the scintillating screen where the principal idea is to fill a matrix of Si pores with a CsI scintillator. The photoluminescence technique was used to prove the wave-guiding property of the matrix and to inspect the filling uniformity of the pores. The final detector was characterized by X-ray evaluation in terms of spatial resolution, light output and SNR. A sensor with a spatial resolution of 9 LP/mm and a SNR over 50 has been achieved using a standard dental X-ray source and doses in the order of those used at the moment by dentists (around 25 mR).
|
|
| 3. |
- Galeckas, Augustinas, et al.
(författare)
-
Investigation of stacking fault formation in hydrogen bombarded 4H-SiC
- 2005
-
Ingår i: SILICON CARBIDE AND RELATED MATERIALS 2004. - 0878499636 ; , s. 327-330
-
Konferensbidrag (refereegranskat)abstract
- The effects of hydrogen and proton irradiation on stacking fault formation in 4H-SiC are investigated by an optical pump-probe method of imaging spectroscopy. We report optically stimulated nucleation and expansion of stacking faults (SFs) in 0.6 keV H-2(+) implanted n-/n+ and p+/n-/n+ structures. The activation enthalpy for recombination enhanced dislocation glide (REDG) in hydrogenated samples (∼ 0.25 eV) is found to be similar to that in a virgin material. Our results indicate that SFs mainly nucleate at the internal n-/n+ interface, beyond reach of hydrogen, thus justifying minor SF passivation effect. No REDG could be initiated optically in 2.5 MeV proton irradiated samples due to radiation defects providing alternative recombination channels to bypass the REDG mechanism. The radiation damage was verified by DLTS, revealing several new levels below E-C in the range 0.4-0.80 eV, and by PL, showing the onset of D-center related luminescence band and concurrent increase of the nonradiative recombination rate.
|
|
| 4. |
- Galeckas, Augustinas, et al.
(författare)
-
Investigation of structural stability in 4H-SiC structures with heavy ion implanted interface
- 2006
-
Ingår i: Silicon Carbide and Related Materials 2005, Pts 1 and 2. - 9780878494255 ; , s. 395-398
-
Konferensbidrag (refereegranskat)abstract
- We investigate the possibility of controlling formation of stacking faults (SFs) at the interface region by implanting the 4H-SiC substrate with low-energy antimony ions (75 keV Sb+) prior to conventional CVD growth of the homoepitaxial layers. This approach is based on the solidsolution hardening concept, according to which interaction of impurity atoms with dislocations makes the motion of the latter more difficult. Photoluminescence imaging spectroscopy is employed to investigate incorporation of Sb+ implants at the buried interface and also to assess its impact on structural degradation. Spectral results are analyzed considering both the onset of n-type doping and irradiation damage. The latter factor was estimated separately from supplementary measurements of high-energy (2.5 MeV H+) proton-irradiated 4H-SiC epilayers. We compare results of optically stimulated SF formation in virgin and Sb implanted regions and provide a comprehensive picture of the defect evolution, including microscopic details of the imminent nucleation sites.
|
|
| 5. |
- Galeckas, Augustinas, et al.
(författare)
-
Optical investigation of the built-in strain in 3C-SiC epilayers
- 2004
-
Ingår i: SILICON CARBIDE AND RELATED MATERIALS 2003, PRTS 1 AND 2. ; , s. 657-660
-
Konferensbidrag (refereegranskat)abstract
- The impact of the residual strain ranging from -2.5 GPa to + 0.436 GPa on the electronic properties of 3C-SiC/Si(100) heteroepitaxial layers is investigated by imaging PL spectroscopy. An anomalous above band-gap emission is observed in the blue/green region of spectrum and is tentatively attributed to the manifestation of defect-rich SiC/Si interfaces. A direct correlation of the accumulated strain with the energy gap and the temperature dependence of the band-gap are determined from the analysis of the peak shifts in the fundamental luminescence spectra. The differential pressure coefficient of the band-gap is found to be dE(G)/dp = -5 meV/GPa at room temperature. The observed energy gap narrowing in the temperature interval from 70 to 320 K can be described by the Varshni equation E-G = 2.417 - alphaT(2) (beta + T)(-1) with the parameters alpha = 3.4x10(-4) eV/K and beta = 700 K.
|
|
| 6. |
- Juhasz, Robert, et al.
(författare)
-
Size-reduced silicon nanowires : Fabrication and electrical characterization
- 2005
-
Ingår i: Materials science & engineering. C, biomimetic materials, sensors and systems. - : Elsevier BV. - 0928-4931 .- 1873-0191. ; 25:5-8, s. 733-737
-
Tidskriftsartikel (refereegranskat)abstract
- Silicon nanowires of diameters down to 100 nm and typical lengths of 1-3 μm have been fabricated in silicon-on-insulator material by electron beam lithography and plasma etching. They were subsequently size-reduced by photoelectrochemical etching resulting in wire widths down to 10 nm. To enable accurate control of the photoelectrochemical size-reduction, a micro-electrochemical cell was developed, enabling single nanowires to be exposed to the etching solution while being illuminated by a laser or a lamp. The arrangement allows contact leads to be extended to metal contact pads located outside the cell, which can be connected by probes, allowing in situ electrical characterization of a nanowire during etching. In this paper, we describe the experimental setup, the fabrication method and show examples of achieved wire widths together with some preliminary results from the electrical characterization.
|
|
| 7. |
- Long, Ethan, et al.
(författare)
-
Nano-structuring in SiGe by oxidation induced anisotropic Ge self-organization
- 2013
-
Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 113:10, s. 104310-
-
Tidskriftsartikel (refereegranskat)abstract
- The present study examines the kinetics of dry thermal oxidation of (111), (110), and (100) silicon-germanium (SiGe) thin epitaxial films and the redistribution of Ge near the oxidation interface with the aim of facilitating construction of single and multi-layered nano-structures. By employing a series of multiple and single step oxidations, it is shown that the paramount parameter controlling the Ge content at the oxidation interface is the oxidation temperature. The oxidation temperature may be set such that the Ge content at the oxidation interface is increased, kept static, or decreased. The Ge content at the oxidation interface is modeled by considering the balance between Si diffusion in SiGe and the flux of Si into the oxide by formation of SiO2. The diffusivity of Si in SiGe under oxidation is determined for the three principal crystal orientations by combining the proposed empirical model with data from X-ray diffraction and variable angle spectroscopic ellipsometry. The orientation dependence of the oxidation rate of SiGe was found to follow the order: (111) > (110) > (100). The role of crystal orientation, Ge content, and other factors in the oxidation kinetics of SiGe versus Si are analyzed and discussed in terms of relative oxidation rates.
|
|
| 8. |
- Ma, Quanbao, et al.
(författare)
-
Boron-implanted 3C-SiC for intermediate band solar cells
- 2016
-
Ingår i: Silicon Carbide and Related Materials 2015. ; , s. 291-294
-
Konferensbidrag (refereegranskat)abstract
- Sublimation-grown 3C-SiC crystals were implanted with 2 atomic percent of boron ions at elevated temperature (400 °C) using multiple energies (100 to 575 keV) with a total dose of 8.5×1016 atoms/cm2. The samples were then annealed at 1400, 1500 and 1600 °C for 1h at each temperature. The buried boron box-like concentration profile can reach ~2×1021 cm-3 in the plateau region. The optical activity of the incorporated boron atoms was deduced from the evolution in absorption and emission spectra, indicating possible pathway for achieving an intermediate band behavior in boron doped 3C-SiC at sufficiently high dopant concentrations.
|
|
| 9. |
- Ma, Quanbao, et al.
(författare)
-
Characterization of B-Implanted 3C-SiC for Intermediate Band Solar Cells
- 2017
-
Ingår i: Materials Science Forum. - : Trans Tech Publications. - 0255-5476 .- 1662-9752. ; 897, s. 299-302
-
Tidskriftsartikel (refereegranskat)abstract
- Sublimation-grown 3C-SiC crystals were implanted with B ions at elevated temperature (400 °C) using multiple energies (100 to 575 keV) with a total dose of 1.3×1017 atoms/cm2 in order to form intermediate band (IB) in 3C-SiC. The samples were then annealed at 1400 °C for 60 min. An anomalous area in the center was observed in the PL emission pattern. The SIMS analysis indicated that the B concentration was the same both within and outside the anomalous area. The buried boron box-like concentration profile can reach ~3×1021 cm-3 in the plateau region. In the anomalous area a broad emission band (possible IB) emerges at around ~1.7-1.8 eV, which may be associated with B-precipitates having a sufficiently high density.
|
|
| 10. |
- Patricia, Carvalho, et al.
(författare)
-
Boron-doping of cubic SiC for intermediate band solar cells: a scanning transmission electron microscopy study
- 2018
-
Ingår i: SciPost Physics. - Amsterdam, Netherlands : SciPost Foundation. - 2542-4653. ; 5:3, s. 1-17
-
Tidskriftsartikel (refereegranskat)abstract
- Boron (B) has the potential for generating an intermediate band in cubic silicon carbide (3C-SiC), turning this material into a highly efficient absorber for single-junction solar cells. The formation of a delocalized band demands high concentration of the foreign element, but the precipitation behavior of B in the 3C polymorph of SiC is not well known. Here, probe-corrected scanning transmission electron microscopy and secondary-ion mass spectrometry are used to investigate precipitation mechanisms in B-implanted 3C-SiC as a function of temperature. Point-defect clustering was detected after annealing at 1273 K, while stacking faults, B-rich precipitates and dislocation networks developed in the 1573 - 1773 K range. The precipitates adopted the rhombohedral B13C2 structure and trapped B up to 1773 K. Above this temperature, higher solubility reduced precipitation and free B diffused out of the implantation layer. Dopant concentrations E19 at.cm-3 were achieved at 1873 K.
|
|
