| 1. |
- Grivickas, Vytautas, et al.
(författare)
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Strong photoacoustic oscillations in layered TlGaSe2 semiconductor
- 2007
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Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 244:12, s. 4624-4628
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Tidskriftsartikel (refereegranskat)abstract
- Periodic deflections of infrared probe are observed in TlGaSe2 after lateral excitation with optical pulse. The effect is explained by generation of photoacoustic dilatational wave, which propagates within the crystal. Low pulse fluence (0.01 mJ/cm(2)) is needed to induce such wave when the layer plane is excited. Acoustic wave is generated within a mu m-distance near the excited face, much shorter then the light penetration depth, 1/alpha, where alpha is the absorption coefficient. In the temperature range 105-120 K, where ferroelectric-paraelectric phase transition occur in TlGaSe2, discontinuous changes of the longitudinal sound velocity have been detected.
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| 2. |
- Gulbinas, Karolis, et al.
(författare)
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Raman Scattering and Carrier Diffusion Study in Heavily Co-doped 6H-SiC Layers
- 2014
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Ingår i: IOP Conference Series. - : Institute of Physics Publishing (IOPP). - 1757-8981 .- 1757-899X. ; 56:1, s. 012005-
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Tidskriftsartikel (refereegranskat)abstract
- Thick 6H-SiC epilayers were grown using the fast sublimation method on low-off-axis substrates. They were co-doped with N and B impurities of ≈1019 cm−3 and (41016–51018) cm−3 concentration, respectively. The epilayers exhibited donor-acceptor pair (DAP) photoluminescence. The micro-Raman spectroscopic study exposed a compensated n-6H-SiC epilayer of common quality with some 3C-SiC inclusions. The compensation ratio of B through 200 μm thick epilayer varied in 20-30% range. The free carrier diffusivity was studied by transient grating technique at high injection level. The determined ambipolar diffusion coefficient at RT was found to decrease from 1.15 cm2/s to virtually 0 cm2/s with boron concentration increasing by two orders.
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| 3. |
- Gulbinas, Karolis, et al.
(författare)
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Surface Recombination Investigation in Thin 4H-SiC Layers
- 2011
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Ingår i: Materials Science-Medziagotyra. - : Kaunas University of Technology (KTU). - 1392-1320 .- 2029-7289. ; 17:2, s. 119-124
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Tidskriftsartikel (refereegranskat)abstract
- n- and p-type 4H-SiC epilayers were grown on heavily doped SiC substrates. The thickness of the p-type layer was 7 mu m and the doping level around 10(17) cm(-3), while the n-type epilayers were 15 mu m thick and had a doping concentration of 3-5x10(15) cm(-3). Several different surface treatments were then applied on the epilayers for surface passivation: SiO(2) growth, Al(2)O(3) deposited by atomic layer deposition, and Ar-ion implantation. Using collinear pump - probe technique the effective carrier lifetimes were measured from various places and statistical lifetime distributions were obtained. For surface recombination evaluation, two models are presented. One states that surface recombination velocity (SRV) is equal on both the passivation/epi layer interface (S(2)) and the deeper interface between the epilayer and the SiC substrate (S(1)), i.e. (S(1) = S(2)). The other model is simulated assuming that SRV in the epilayer/substrate (S(1)) interface is constant while in the passivation layer/epilayer (S(2)) interface SRV can be varied S(2) < S(1). Empirical nomograms are presented with various parameters sets to evaluate S(2) values. We found that on the investigated 4H-SiC surfaces S(2) ranges from 3x10(4) to 5 x 10(4) assuming that the bulk lifetime is 4 mu s. In Ar(+) implanted surfaces S(2) is between (10(5)-10(6)) cm/s.
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| 4. |
- Usman, Muhammad, et al.
(författare)
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Effect of nuclear scattering damage at the SiO2/SiC and Al2O3/SiC interface : A radiation hardness study of dielectrics
- 2012
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Ingår i: Silicon Carbide And Related Materials 2011, Pts 1 And 2. - : Trans Tech Publications Inc.. ; , s. 805-808
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Konferensbidrag (refereegranskat)abstract
- The radiation hardness of Al2O3 as a dielectric for SiC surface passivation is studied and compared to SiO2 for potential application in radiation hard SiC devices. SiO2 is deposited on 4H-SiC by PECVD and post annealed in N2O, whereas Al2O3 is deposited by atomic layer deposition (ALD). The oxides are bombarded with Ar ions in an energy range to produce maximum damage near the oxide/SiC interface. Metal-insulator-semiconductor structures are prepared and their dielectric characteristics are analyzed using capacitance-voltage measurements. Additionally, the effect of the interface damage on surface recombination is studied using the optical free carrier absorption method for the same samples. The results indicate that the SiO2/SiC interface is significantly affected at 1×1011 cm-2 fluence of Ar ions, however, the dielectric properties of Al2O3/SiC interface remain unaffected even for ten times higher fluences. Similar observations are made for the surface recombination measurements.
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