Residual impurities and native defects in 6H-SiC bulk crystals grown by halide chemical-vapor deposition

Abstract

A variety of defect-sensitive techniques have been employed to detect, identify, and quantify the residual impurities and native defects in high-purity (undoped) 6H-SiC crystals grown by halide chemical-vapor deposition technique. The incorporation efficiencies of N and B are determined by the site-competition effect. Most notably, material with low residual N levels (∼1014cm−3) can be produced. In addition, the nitrogen concentrations obtained from Hall-effect measurements and low-temperature photoluminescence are systematically lower than those determined from secondary-ion-mass spectrometry. The difference is ascribed to nitrogen forming complexes with native defects. The energy level of this complex is approximately 0.27eV below the conduction band. Four major electron traps with activation energies of 0.4, 0.5, 0.65, and 1eV and five hole traps with activation energies of 0.3, 0.4, 0.55, 0.65, and 0.85eV were observed by deep-level transient spectroscopy. The concentration of all traps decreased strongly with increasing C∕Si ratio during growth. Increasing the C∕Si flow ratio also led to increased resistivity of the crystals and change of conductivity from conductive n type to high-resistivity p type. The Fermi level in p-type material is pinned either to highly compensated shallow B acceptors or to deep B-related center at 0.6eV above the valence band. Electron paramagnetic resonance shows the presence of positively charged carbon vacancies in such high-resistivity material.

Investigation of defect levels in 6H‐SiC single crystals

“…Moreover, the concentration of the 0.7-eV trap was found to be much higher at the seed end than at the tail end of the crystals [5]. In view of the reported results [5,6], trap T4 seems to be related to silicon interstitials. Figure 4 shows the PITS spectra for three defect centers labeled as TP1, TP2 and TP3 detected in the samples of bulk 6H-SiC:N. Fig.…”

“…Moreover, the concentration of the 0.5-eV trap was found to be higher when the gas phase during the crystal growth was more Si-rich [5,6]. The concentration of this trap was also found to be by more than an order of magnitude higher in the seed portion of the boules compared to that in the tail portion.…”

“…The trap T4 (E c -0.69 eV) has been previously observed in 6H-SiC bulk crystals as the grown-in 0.7-eV electron trap [6]. Moreover, the concentration of the 0.7-eV trap was found to be much higher at the seed end than at the tail end of the crystals [5].…”

“…16 0.7-eV trap related to silicon interstitials [5,6] The trap T1 (E c -0.53 eV) is likely to be the 0.5-eV trap that has been earlier observed by Polyakov et al [5] and Huh et al [6] in as grown, n-type bulk 6H-SiC crystals. Moreover, the concentration of the 0.5-eV trap was found to be higher when the gas phase during the crystal growth was more Si-rich [5,6].…”

“…Thus, the traps T1 (E c -0.53 eV) can be attributed to carbon vacancies located in the vicinity of dislocations or in the dislocation core. The traps T2 (E c -0.64 eV) and T3 (E c -0.67 eV) can be identified with the known electron traps Z 1 (E c -0.62 eV) and Z 2 (E c -0.64 eV), respectively, which are characteristic of both 4H-and 6H-SiC [5][6][7]. In some reports, however, the Z 1 and Z 2 traps are not resolved and the broad DLTS peak, composed of two overlapping electron-emission peaks, is observed [5,6] and is assumed to be related to a Z 1 /Z 2 defect center.…”