Papers by Keyword: Intrinsic Defect

Abstract: Carrier lifetime and formation of defects have been investigated as a function of growth temperature in n-type 4H-SiC epitaxial layers, grown by horizontal hot-wall CVD. Emphasis has been put on having fixed conditions except for the growth temperature, hence growth rate, doping and epilayer thickness were constant in all epilayers independent of growth temperature. An increasing growth temperature gave higher Z1/2 concentrations along with decreasing carrier lifetime. A correlation between growth temperature and D1 defect was also observed.

Abstract: In this paper the impact of high temperature annealing on the formation of intrinsic defects in 4H-SiC such as Z_1/2 and EH_6/7 was examined. Therefore, three epitaxial layers with various initial concentrations of the Z_1/2- and EH_6/7-centers (10¹¹ – 10¹³ cm^-3) were investigated. It turns out that depending on the initial defect concentration the high temperature annealing leads to a monotone increase of the Z_1/2- and EH_6/7-concentration in a temperature range from 1600 to 1750°C. For a defined temperature above these values, the resulting defect concentration is independent of the sample’s initial values. Beside the growth conditions themselves such as C/Si ratio the thermal post-growth processing has a severe impact on the carrier lifetime which must be taken into account during device fabrication.

Abstract: 4H-SiC has been irradiated with 10 keV protons and a laterally resolved DLTS study performed to study the diffusion of irradiation induced intrinsic point defects. It is found that the defects migrate on the order of hundreds of μm laterally and carbon interstitials (CI) are believed to be involved in the defect formation. However, the vertical diffusion lengths are revealed to be several orders of magnitude shorter, on the order of hundreds of nm. Specifically, the Z1,2, S1,2 and EH6,7 levels are found to be generated significant distances from the irradiated area, suggesting that CI or another highly mobile species are involved in the formation of these defects.

Abstract: In this paper the new method for determination of luminescent centers concentration are discussed. While the possibility of electron traps determination and definition of its activation energy are suggested. The cathodoluminescent (CL) method was used. The determination of luminescent centers concentration in silicon oxide is based on the measurements of dependences of CL intensity on electron beam current. The presence and energy of activation of electron traps were studied by measurement of rise time and decay of luminescent band during the stationary irradiation of silica by electron beam.

Abstract: To determine the energy levels of intrinsic defects in high-purity semi-insulating 4H-SiC, we apply discharge current transient spectroscopy (DCTS) that is a graphical peak analysis method based on the transient reverse current of a Schottky barrier diode, because transient capacitance methods such as deep level transient spectroscopy and isothermal capacitance transient spectroscopy are feasible only in low-resistivity semiconductors. Seven intrinsic defects are detected in the high-purity semi-insulating 4H-SiC. From the temperature dependence of the emission rate of each intrinsic defect, its activation energy is approximately determined.

Abstract: Defects introduced by electron irradiation at ~80-100 K in 3C-, 4H- and 6H-SiC were studied by electron paramagnetic resonance (EPR). A number of EPR spectra, labelled LE1-10, were detected. Combining EPR and supercell calculations, we will show that the LE1 center in 3C-SiC with C2v symmetry and an electron spin S=3/2 is related to the (VSi-Sii)3+ Frenkel pair between the silicon vacancy and a second neighbour Sii interstitial along the <100> direction. Results on other centers, possibly also related to interstitials, are discussed.

Abstract: Chloride-based 4H-SiC epitaxial layers were investigated by DLTS, MCTS and PL. The DLTS spectra of the as grown samples showed dominance of the Z1/2 and the EH6/7 peaks. For growth rates exceeding 100 µm/h, an additional peak occurred in the DLTS spectra which can be assigned to the UT1 defect. The shallow and the deep boron complexes as well as the HS1 defect are observed in MCTS measurements. The PL spectra are completely dominated by the near band gap (NBG) emission. No luminescence from donor-acceptor pair occurred. The PL line related to the D1 centre was weakly observed. In the NBG region nitrogen bound exciton (N-BE) and free exciton (FE) related lines could be seen. The addition of chlorine in the growth process gives the advantage of high growth rates without the introduction of additional defects.

Abstract: The Tv2a center in 4H-SiC irradiated by electrons at room temperature has been studied by pulsed EPR. Various techniques such as pulsed ELDOR (electron-electron double resonance), 2-pulse echo decay, 3-pulse inversion recovery, pulsed ENDOR (electron nuclear double resonance), and 3-pulse ESEEM (electron spin echo envelope modulation) have been applied to perform the detailed structure determination and to exploit applicability for the coherent spin control experiments.

Abstract: We have studied annealing of the main lifetime limiting defect Z1/2 in thick 4H-SiC epilayers by the application of carbon-implantation/annealing method. Examination of different implantation doses and annealing temperatures showed that finding the optimum conditions is crucial for obtaining carrier trap concentration below 1011 cm-3 in the whole 100 μm epilayer. The carrier lifetime increased from under 200 ns to over 1 μs at room temperature in the samples prepared by optimized carbon-implantation/annealing technique. Fabrication of pin diodes from the improved thick 4H-SiC epilayers confirmed the enhanced conductivity modulation and suitability of this technique for high-voltage bipolar SiC devices.

Abstract: Semi-insulating (SI) 4H-SiC substrates doped with vanadium (V) in the range 5.5×1015 –1.1×1017 cm–3 were studied by electron paramagnetic resonance. We show that only in heavily V-doped 4H-SiC vanadium is responsible for the SI behavior, whereas in moderate V-doped substrates with the V concentration comparable or slightly higher than that of the shallow N donor or B acceptor, the SI properties are thermally unstable and determined by intrinsic defects. The results show that the commonly observed thermal activation energy Ea~1.1 eV in V-doped 4H-SiC, which was previously assigned to the single acceptor V4+/3+ level, may be related to deep levels of the carbon vacancy. Carrier compensation processes involving deep levels of V and intrinsic defects are discussed and possible thermal activation energies are suggested.