Deep Levels in As-Grown and Electron-Irradiated P-type 4H-SiC
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0911-B06-04
Deep Levels in As-Grown and Electron-Irradiated P-type 4H-SiC Katsunori Danno, and Tsunenobu Kimoto Department of Electronic Science and Engineering, Kyoto University, Kyotodaigaku-katsura, Nishikyo, Kyoto, 615-8510, Japan ABSTRACT Deep levels in as-grown and electron-irradiated p-type 4H-SiC have been investigated by deep level transient spectroscopy (DLTS). Three hole traps, namely HK2, HK3, and HK4, could be detected in the temperature range from 350K to 700K. Activation energies of the hole traps were estimated to be 0.84 eV for HK2, 1.27 eV for HK3, and 1.44 eV for HK4 from the Arrhenius plot of emission-time constants assuming temperature-independent capture cross section. By double-correlated DLTS (DDLTS), they were revealed to be donor-like (+/0) traps. The concentrations of HK3 and HK4 centers were clearly increased by low-energy (116 keV) electron irradiation. Based on thermal stability of the HK3 and HK4 centers up to 1350°C and the dependence of HK4 concentration on the electron fluence, they may originate from a complex including defect(s) caused by carbon displacement. INTRODUCTION To realize high-performance power devices, deep levels should be decreased because deep levels act as carrier recombination and generation centers. Control of deep levels is also essential to reproducibly obtain high-purity semi-insulating substrates [1, 2]. In high-quality n-type 4H-SiC epilayers, Z1/2 (Ec – 0.65 eV) [3] and EH6/7 (Ec – 1.55 eV) [4] centers are two major deep levels. While the deep levels in n-type SiC have been extensively investigated, limited information is available about deep levels detected in p-type epilayers (hole traps) [5]. Study on hole traps is essential for developing SiC bipolar devices because hole traps possibly act as minority carrier (hole) traps in active layers (n-layers) of most SiC bipolar devices. In this work, we have investigated deep hole traps in both as-grown and electron-irradiated p-type 4H-SiC epilayers by deep level transient spectroscopy (DLTS). The charge state and thermal stability are also investigated. EXPERIMENTAL DETAILS Samples used in this study were commercially available Al-doped 4H-SiC(0001) epilayers grown on p-type substrates by chemical vapor deposition (CVD). The net acceptor concentration of the 10 µm-thick epilayers was 0.5-1.5 × 1016 cm-3. B-doped p-type epilayers with a net
acceptor concentration of 1.6 × 1016 cm-3 were also used, which were grown in the authors’ group. Titanium was employed as a Schottky metal (1.5 mmφ), because high barrier height (about 2.1 eV) could be obtained on p-type SiC, by which leakage current was suppressed even at the very high temperature of 700K. Ti/Al ohmic contacts were formed on the backside of the samples by thermal evaporation followed by rapid thermal annealing at 950°C. Fourier transform DLTS measurements [6] were carried out in the temperature range from 350K to 700K. Double-correlated DLTS (DDLTS) was employed to study charge states of deep hole traps. We also studied thermal stability of deep hole tr
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