Low Energy Electron Irradiation Induced Deep Level Defects in6H−SiC: The Implication for the Microstructure of the Deep LevelsE1/E2

Abstract

N-type 6H-SiC samples irradiated with electrons having energies of E e 0:2, 0:3, 0:5, and 1:7 were studied by deep level transient technique. No deep level was detected at below 0.2 MeV irradiation energy while for E e 0:3 MeV, deep levels ED1, E 1 =E 2 , and E i appeared. By considering the minimum energy required to displace the C atom or the Si atom in the SiC lattice, it is concluded that generation of the deep levels E 1 =E 2 , as well as ED1 and E i , involves the displacement of the C atom in the SiC lattice. DOI: 10.1103/PhysRevLett.92.125504 PACS numbers: 61.72.Ji, 61.80.Fe, 81.05.Je Silicon carbide (SiC) is a promising wide band gap material for fabricating high-temperature, highpower, and high-frequency electronic devices [1]. Deep level defects induced by ion implantation or particle irradiation have been extensively studied because of their great influence on the materials' electrical and optical properties. A general classification for ion implanted or particle irradiated n-type 6H-SiC includes levels ED1 ( E C -0:27 eV), E i ( E C -0:51 eV), E 1 =E 2 ( E C -0:34=0:44 eV, with the name of Z 1 =Z 2 for 4H-SiC), and Z 1 =Z 2 ( E C -0:58=0:72 eV, with the name of E 1 =E 2 for 4H-SiC) [2 -9]. Information involving the microstructures of these deep levels is controversial and incomplete. The E 1 =E 2 doublet is not only the most dominant but also appears to be the most thermal stable in electron irradiated n-type 6H-SiC. The microstructure responsible for this level has been attributed to [6,9], and N i -C i complex [10].All previous deep level transient spectroscopy (DLTS) studies on electron irradiated 6H-SiC materials usually involved high energy electron irradiations (>MeV). Such investigations induce defect types originating from both C and Si atoms displacement and thus provide no basis for discriminating between primary vacancy defects originating on either sublattice. Since the C atom has a significantly smaller mass than that of Si atom (Si=C 2:33), the maximum energy transferred from the electron to the C atoms in the SiC lattice during elastic collision is larger than that of the Si atom. This implies the value of the minimum electron energy for creating the defect V C , originating from displacing a C atom, would be lower than that for creating the defect V Si . This idea has been nicely demonstrated recently by Rempel et al. [11]. Using both positron lifetime and coincident Doppler broadening techniques, it was shown that for low electron irradiation energy 0:5 MeV > E e > 0:3 MeV, only V C was generated, while at higher energy (E e > 0:5 MeV), V Si could also be detected [11]. The precise values of threshold electron irradiation energies for displacement of either the C or the Si atoms are difficult to estimate since they depend to some extent on the conduction type, the growth techniques, or the relative orientation of crystallographic planes of the sample to the incident electron direction and on sample temperature. Nevertheless, the approximate values given above can provide helpful...

Major deep levels with the same microstructures observed in n-type 4H–SiC and 6H–SiC

“…By such low-energy e − -irradiation, only carbon atom displacement can take place in SiC crystals. 10 Although several groups studied radiation-induced defects in 6H-SiC, 3,11,12,[15][16][17][18][19][20][21] there are no reports on deep levels in 6H-SiC irradiated with such low-energy electrons. In this study, the authors detected several traps in both 4H-SiC and 6H-SiC after the e − -irradiation.…”

Effects of Electron Irradiation on Deep Centers in High-Purity Semi-Insulating 6H-SiC

“…16 The HS1 hole trap at E V + 0.35 eV, measured by minority carrier transient spectroscopy (a variation of DLTS), has been associated with the well-known D 1 defect in (3) three V lines in 10 K PL spectra can be only seen in the sample with 1.7-MeV EI, but not in the sample with 0.3-MeV EI. 4 Thus, the authors argued that the ED1, E 1 /E 2 , and E i centers are associated with atom displacement on the C sublattice in 6H-SiC and have a microstructure containing carbon vacancy or carbon interstitial. In order to fully understand the nature of EI-induced TSC/DLTS centers and the correlation between PL lines and DLTS/TSC centers in irradiated conductive and semi-insulating 6H-SiC materials, more studies, including studying defects using low-energy EI in conjunction with other characterization techniques (such as positron annihilation spectroscopy 18 ) and studying the annealing behavior of irradiation-induced traps, are needed.…”

“…[1][2][3][4] Several EI-induced centers have been consistently observed in n-type 6H-SiC with energies ranging from 0.20 to 1.45 eV below the conduction band. Common designations of these centers, following Balandovich 3 and Chen, 4 are ED1 (0.23 eV), E 1 /E 2 (0.34/0.40 eV), E i (0.50 eV), Z 1 /Z 2 (0.62/0.64 eV), L 9 (0.81 eV), L 10 (1.27 eV), and L 11 (1.45 eV).…”

E 1/E2 traps in 6H-SiC studied with Laplace deep level transient spectroscopy

“…[3][4][5] It is well established that the magnitude of the E 1 /E 2 DLTS peak is increased by both ion implantation and electron irradiation. [3][4][5][6][7][8][9][10] The peak also has a shoulder indicating that it is not a single point defect. Previously, the peak has been separated into two components, and the corresponding activation energies for electron emission determined by fitting the DLTS spectra calculated using a two-trap model or by employing the three-point-correlation window DLTS method, 11 which has an improved energy resolution in comparison with conventional DLTS.…”

“…This low-energy e À -irradiation results in the selective displacement of carbon atoms in SiC crystals. 10,18,19 After the e À -irradiation, the samples were annealed in an argon ambient at 950 C for 30 min. In the conventional DLTS and LDLTS measurements, we typically used the reverse bias V r ¼ À7 V, pulse voltage V p ¼ 0 V, and filling pulse width t p ¼ 1 ms. Figure 1 shows a conventional DLTS spectrum for an unirradiated p þ n diode and two spectra for electron-irradiated SBD samples.…”