Papers by Keyword: Semi-insulating (SI)

Abstract: Contactless topographic resistivity mapping is used to characterize SiC and Cd(Zn)Te wafer material. For locally inhomogeneous material, detailed analysis of the deformed charge transients allows the evaluation of the partial resistivity contributions.

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.

Abstract: High-purity, semi-insulating 6H-SiC substrates grown by high-temperature chemical vapor deposition were studied by electron paramagnetic resonance (EPR). The carbon vacancy (VC), the carbon vacancy-antisite pair (VCCSi) and the divacancy (VCVSi) were found to be prominent defects. The (+|0) level of VC in 6H-SiC is estimated by photoexcitation EPR (photo-EPR) to be at ~ 1.47 eV above the valence band. The thermal activation energies as determined from the temperature dependence of the resistivity, Ea~0.6-0.7 eV and ~1.0-1.2 eV, were observed for two sets of samples and were suggested to be related to acceptor levels of VC, VCCSi and VCVSi. The annealing behavior of the intrinsic defects and the stability of the SI properties were studied up to 1600°C.

Abstract: II-VI is developing large-diameter SiC crystals to be used as lattice-matched, high thermal conductivity substrates for new generation GaN-based and SiC-based semiconductor devices. Large-diameter 6H SiC single crystals are grown at II-VI using our Advanced PVT sublimation growth process. Stable SI properties are achieved by compensation with vanadium, which results in high and spatially uniform resistivity, on the order of 1011 Ohm-cm. The quality of the presently grown 100 mm 6H SI substrates has been dramatically improved [1], and they are free of edge defects. Micropipe density in the 100 mm 6H SI substrates ranges from 2 to 8 cm-2 and dislocation density from 3·104 to 6·104 cm-2. X-ray rocking curves measured on as-sawn 100 mm 6H wafers showed edge-to-edge lattice curvature () between 0.1° and 0.3° and FWHM of the rocking curve between 50 and 100 arc-seconds

Abstract: Vacancies, divacancies and carbon vacancy-carbon antisite pairs are found by electron paramagnetic resonance (EPR) to be dominant defects in high-purity semi-insulating (HPSI) 4HSiC substrates having different thermal activation energies of the resistivity ranging from ~0.8 eV to ~1.6 eV. Based on EPR results and previously reported data, the energy positions of several acceptor states of the vacancies and vacancy-related complexes are estimated. These deep levels are suggested to be associated to different thermal activation energies and responsible for the semiinsulating behaviour in HPSI SiC substrates. Their role in carrier compensation is discussed.

Abstract: The SI-5 electron-paramagnetic-resonance (EPR) centre is a dominant defect in some high-purity semi-insulating (HPSI) SiC substrates and has recently been shown to originate from the negatively charged carbon vacancy-carbon antisite pair (VC − Si C ). In this work, photoexcitation EPR (photo-EPR) was used for determination of the energy position of deep acceptor levels of VCCSi in 4H-SiC. Our photo-EPR measurements in slightly n-type material show an increase of the EPR signal of VC − Si C for photon energies from ~0.8 eV to ~1.3 eV. Combining the data from EPR, deep level transient spectroscopy and supercell calculations we suggest that the (1–|2–) levels of the different configurations of the defect are located in the range ~0.8-1.1 eV below the conduction band.

Abstract: The authors attempted to grow a semi-insulating SiC epitaxial layer by in-situ vanadium doping. The homoepitaxial growth of the vanadium-doped 4H-SiC layer was performed by MOCVD using the organo-silicon precursor, bis-trimethylsilylmethane (BTMSM, [C7H20Si2]) and the metal-organic precursor, bis-cyclopentadienylvanadium (Verrocene, [C10H10V]). Vanadium doping effect on crystallinity of epilayer was very destructive. Vanadium-doped epilayers grown on normal condition had various surface or crystal defects such as micropipes, polytype inclusions. But this crystallinity degradation was overcome by high growth temperature. For the measurement of the resistivity of the highly resistive vanadium-doped 4H-SiC epilayers, the authors used the on-resistance technique. Based on the measurements of the on-resistance of the epilayers using the current-voltage technique, it is shown that the residual donor concentration of the epilayers was decreased with increasing partial pressure of verrocene. The resistivity of the vanadium-doped 4H-SiC epilayer was about 107 /cm.

Abstract: A room temperature PL mapping technique was applied to establish the origin of resistivity variation in PVT-grown 6H SiC substrates. A direct correlation between the native defect-related PL and resistivity was found in undoped (V-free) samples. In vanadium-doped samples with low vanadium content, the resistivity showed a good correlation with the total PL signal consisting of contributions from both vanadium and native point defects. Well-known UD1 and UD3 levels were revealed by low-temperature PL spectroscopy. Some correlation was observed between these low-temperature PL signatures and the resistivity distribution.

Abstract: Semi-insulating SiC grown by the HTCVD technique are studied by luminescence and absorption measurements and the results are compared to PAS and SIMS results. We have found that metal impurities are present but only in very small concentrations. The semi-insulating properties are instead determined by the intrinsic defects, mostly the silicon vacancy in hydrocarbon rich grown material and the carbon vacancy in the hydrocarbon poor grown material. The hydrocarbon poor material is stable upon annealing both from a vacancy concentration point of view and from a resistivity point of view. The hydrocarbon rich grown material does not stand the annealing at 1600 °C and the resistivity is decreased; from the absorption and PAS measurements we have observed that the decrease in silicon vacancy concentration fits the growth of the vacancy clusters.

Abstract: In this paper, we attempted to grow semi-insulating SiC epitaxial layer by in-situ iron doping. Homoepitaxial growth of iron-doped 4H-SiC layer was performed by MOCVD using organo-silicon precursor, bis-trimethylsilylmethane (BTMSM, [C7H20Si2]) and metal organic precursor, t-butylferrocene ([C14H17Fe]). Doping-induced crystallinity degradation showed different tendency depending on conducting type of substrate. The crystal quality of epilayer grown on n-type substrate was not degraded significantly despite of the Fe doping but in case of semi-insulating substrate, crystallinity was remarkably degraded as increasing iron contents. For measurement of resistivity of highly resistive iron-doped 4H-SiC epilayer, we used the on-resistance technique which is firstly attempted for measuring resistivity of epilayer. From on-resistance of epilayer measured by I-V, it is shown that the residual donor concentration of epilayer was decreased as increasing partial pressure of t-butylferrocene. The resistivity of iron-doped 4H-SiC epilayer was about 107 Ωcm. From this result, it is concluded that Fe could effectively act as a compensation center in the iron-doped 4H-SiC.