| 21. |
- Ewing, D.J., et al.
(författare)
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Inhomogeneous electrical characteristics in 4H-SiC Schottky diodes
- 2007
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Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 22:12, s. 1287-1291
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Tidskriftsartikel (refereegranskat)abstract
- Hundreds of current-voltage (I-V) measurements of Ni, Pt and Ti Schottky diodes on 4H-SiC were conducted at low applied voltages. The SiC substrates contained homoepitaxial layers grown by either chemical vapor deposition or sublimation. While near-ideal contacts were fabricated on all samples, a significant percentage of diodes (∼7%-50% depending on the epitaxial growth method and the diode size) displayed a non-ideal, or inhomogeneous, barrier height. These 'non-ideal' diodes occurred regardless of growth technique, pre-deposition cleaning method, or contact metal. In concurrence with our earlier reports in which the non-ideal diodes were modeled as two Schottky barriers in parallel, the lower of the two Schottky barriers, when present, was predominantly centered at one of the three values: ∼0.60, 0.85 or 1.05 eV. The sources of these non-idealities were investigated using electron-beam- induced current (EBIC) and deep-level transient spectroscopy (DLTS) to determine the nature and energy levels of the defects. DLTS revealed a defect level that corresponds with the low- (non-ideal) barrier height, at ∼0.60 eV. It was also observed that the I-V characteristics tended to degrade with increasing deep-level concentration and that inhomogeneous diodes tended to contain defect clusters. Based on the results, it is proposed that inhomogeneities, in the form of one or more low-barrier height regions within a high-barrier height diode, are caused by defect clusters that locally pin the Fermi level. © 2007 IOP Publishing Ltd.
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| 22. |
- Galeckas, A., et al.
(författare)
-
Optical and microstructural investigation of heavy B-doping effects in sublimation-grown 3C-SiC
- 2018
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Ingår i: Materials Science Forum. - : Trans Tech Publications Ltd. - 9783035711455 ; , s. 221-224
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Konferensbidrag (refereegranskat)abstract
- In this work, a complementary microstructural and optical approach is used to define processing conditions favorable for the formation of deep boron-related acceptor centers that may provide a pathway for achieving an intermediate band behavior in highly B-doped 3C-SiC. The crystallinity, boron solubility and precipitation mechanisms in sublimation-grown 3C-SiC crystals implanted to 1-3 at.% B concentrations were investigated by STEM. The revealed defect formation and boron precipitation trends upon thermal treatment in the range 1100-2000oC have been crosscorrelated with the optical characterization results provided by imaging PL spectroscopy. We discuss optical activity of the implanted B ions in terms of both shallow acceptors and deep D-centers, a complex formed by a boron atom and a carbon vacancy, and associate the observed spectral developments upon annealing with the strong temperature dependence of the D-center formation efficiency, which is further enhanced by the presence of implantation-induced defects. © 2018 Trans Tech Publications, Switzerland.
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| 23. |
- Gavryushin, V., et al.
(författare)
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Examination of Photoluminescence Temperature Dependencies in N-B Co-doped 6H-SiC
- 2014
-
Ingår i: IOP Conference Series. - : Institute of Physics Publishing (IOPP). - 1757-8981 .- 1757-899X. ; 56:1, s. 012003-
-
Tidskriftsartikel (refereegranskat)abstract
- Two overlapping photoluminescent (PL) bands with a peaks (half-width) at 1.95 eV (0.45 eV) and 2.15 eV (0.25 eV), correspondingly at 300 K, are observed in heavily B-N co-doped 6H-SiC epilayers under high-level excitation condition. The low energy band dominates at low temperatures and decreases towards 300 K which is assigned to DAP emission from the nitrogen trap to the deep boron (dB) with phonon-assistance. The 2.15 eV band slightly increases with temperature and becomes comparable with the former one at 300 K. We present a modelling comprising electron de-trapping from the N-trap, i.e. calculating trapping and de-trapping probabilities. The T-dependence of the 2.15 eV band can be explained by free electron emission from the conduction band into the dB center provided by similar phonon-assistance
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| 24. |
- Glans, P.-A., et al.
(författare)
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Core level and valence band photoemission study of the (1 1 1) and (1¯ 1¯ 1¯) surfaces of 3C-SiC
- 2001
-
Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 470:3, s. 284-292
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Tidskriftsartikel (refereegranskat)abstract
- A core level and valence band photoemission study of thick 3C-SiC(1 1 1) and 3C-SiC(1¯ 1¯ 1¯) epilayers grown by sublimation epitaxy is reported. The as introduced samples show threefold 1×1 low-energy electron diffraction patterns. For the Si face v3 and 6v3 reconstructed surfaces develop after in situ heating to 1100 °C and 1300 °C, respectively. For the C face a 3×3 reconstruction form after heating to 980 °C. A semiconducting behavior is observed for the v3 and 3×3 reconstructed surfaces while the 6v3 reconstruction show a Fermi edge and thus a metallic-like behavior. The surface state on the v3 surface is investigated and found to have ?1 symmetry and a total band width of 0.10 eV within the first surface Brillouin zone. For the Si2p and C 1s core levels binding energies and surface shifted components are extracted and compared to earlier reported results for 6H- and 4H-SiC.
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| 25. |
- Grivickas, P., et al.
(författare)
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Carrier lifetime investigation in 4H-SiC grown by CVD and sublimation epitaxy
- 2001
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Ingår i: Materials Science in Semiconductor Processing. - 1369-8001 .- 1873-4081. ; 4:03-jan, s. 191-194, s. 191-194
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Tidskriftsartikel (refereegranskat)abstract
- Depth-resolved carrier lifetime measurements were performed in low-doped epitaxial layers of 4H silicon carbide samples. The technique used was a pump-and-probe technique where carriers are excited by an above-bandgap laser pulse and probed by free carrier absorption. Results from chemical vapour deposition samples show that lifetimes as high as 2 mus may be observed in the mid-region of 40 mum thick epilayers. For epilayers grown by the sublimation method decay transients were characterised by a fast (few nanoseconds) initial recombination, tentatively assigned to the 'true' lifetime, whereas a slow tail of several hundred microsecond decay time was assigned to trapping centres. From the saturation of this level at increased pumping we could derive the trapping concentration and their depth distribution peaking at the epilayer/substrate interface.
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| 26. |
- Grivickas, V., et al.
(författare)
-
Carrier lifetimes and influence of in-grown defects in N-B Co-doped 6H-SiC
- 2014
-
Ingår i: IOP Conference Series. - : Institute of Physics Publishing (IOPP). ; 56:1, s. 012004-
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Konferensbidrag (refereegranskat)abstract
- The thick N-B co-doped epilayers were grown by the fast sublimation growth method and the depth-resolved carrier lifetimes have been investigated by means of the free-carrier absorption (FCA) decay under perpendicular probe-pump measurement geometry. In some samples, we optically reveal in-grown carbon inclusions and polycrystalline defects of substantial concentration and show that these defects slow down excess carrier lifetime and prevent donor-acceptor pair photo luminescence (DAP PL). A pronounced electron lifetime reduction when injection level approaches the doping level was observed. It is caused by diffusion driven non-radiative recombination. However, the influence of surface recombination is small and insignificant at 300 K.
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| 27. |
- Grivickas, V, et al.
(författare)
-
Thermopower measurements in 4H-SiC and theoretical calculations considering the phonon drag effect
- 2001
-
Ingår i: Materials Science Forum, Vols. 353-356. ; , s. 491-494
-
Konferensbidrag (refereegranskat)abstract
- The Seebeck coefficient study in a heavily nitrogen-doped n-type 4H-SiC epilayer in the direction perpendicular to c-axis is presented. The Seebeck coefficient steeply increases from 0.56 mV/K to 1.7 mV/K with decreasing temperature in the range 400-80 R. This behavior is explained by the phonon drag effect. An approach to the theoretical modeling of the phonon drag effect is discussed and simulation of the Seebeck coefficient temperature-dependence is displayed.
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| 28. |
- Gulbinas, Karolis, et al.
(författare)
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Raman Scattering and Carrier Diffusion Study in Heavily Co-doped 6H-SiC Layers
- 2014
-
Ingår i: IOP Conference Series. - : Institute of Physics Publishing (IOPP). - 1757-8981 .- 1757-899X. ; 56:1, s. 012005-
-
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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| 29. |
- Gällström, Andreas, 1978-, et al.
(författare)
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Influence of Cooling Rate after High Temperature Annealing on Deep Levels in High-Purity Semi-Insulating 4H-SiC
- 2007
-
Ingår i: Materials Science Forum, vol. 556-557. - : Trans Tech Publications. ; , s. 371-
-
Konferensbidrag (refereegranskat)abstract
- The influence of different cooling rates on deep levels in 4H-SiC after high temperature annealing has been investigated. The samples were heated from room temperature to 2300°C, followed by a 20 minutes anneal at this temperature. Different subsequent cooling sequences down to 1100°C were used. The samples have been investigated using photoluminescence (PL) and IV characteristics. The PL intensities of the silicon vacancy (VSi) and UD-2, were found to increase with a faster cooling rate.
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| 30. |
- Henry, Anne, et al.
(författare)
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Presence of hydrogen in SiC
- 2001
-
Ingår i: Materials Science Forum, Vols. 353-356. ; , s. 373-376, s. 373-376
-
Konferensbidrag (refereegranskat)abstract
- An unexpected presence of hydrogen in 4H-SiC was revealed by the observation of hydrogen related lines in the low-temperature photoluminescence (LTPL) spectrum after secondary ion mass spectrometry (SIMS) measurements. The lines were not observed before SIMS. The high-energy ions during SIMS are proposed to break the boron-hydrogen bonds. This phenomenon is observable only for a certain impurity concentration in the material due to the competition of various recombination channels during the LTPL experiment.
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