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In this study, to reveal the origin of the Z½ center, a lifetime killer in n-type 4H-SiC, the concentrations of the Z½ center and point defects are compared in the same samples, using deep level transient spectroscopy (DLTS) and electron paramagnetic resonance (EPR). The Z½ concentration in the samples is varied by irradiation with 250 keV electrons with various fluences. The concentration of a single carbon vacancy (VC) measured by EPR under light illumination can well be explained with the Z½ concentration derived from C-V and DLTS irrespective of the doping concentration and the electron fluence, indicating that the Z½ center originates from a single VC. [ABSTRACT FROM AUTHOR]

Two trap-reduction processes, thermal oxidation and C+ implantation followed by Ar annealing, have been discovered, being effective ways for reducing the Z1/2 center (EC - 0.67 eV), which is a lifetime killer in n-type 4H-SiC. In this study, it is shown that new deep levels are generated by the trap-reduction processes in parallel with the reduction of the Z1/2 center. A comparison of defect behaviors (reduction, generation, and change of the depth profile) for the two trap-reduction processes shows that the reduction of deep levels by thermal oxidation can be explained by an interstitial diffusion model. Prediction of the defect distributions after oxidation was achieved by a numerical calculation based on a diffusion equation, in which interstitials generated at the SiO2/SiC interface diffuse to the SiC bulk and occupy vacancies related to the origin of the Z1/2 center. The prediction based on the proposed analytical model is mostly valid for SiC after oxidation at any temperature, for any oxidation time, and any initial Z1/2-concentration. Based on the results, the authors experimentally achieved the elimination of the Z1/2 center to a depth of about 90 μm in the sample with a relatively high initial-Z1/2-concentration of 1013 cm-3 by thermal oxidation at 1400 °C for 16.5 h. Furthermore, prediction of carrier lifetimes in SiC from the Z1/2 profiles was realized through calculation based on a diffusion equation, which considers excited-carrier diffusion and recombination in the epilayer, in the substrate, and at the surface. [ABSTRACT FROM AUTHOR]

The authors have investigated effects of thermal oxidation on deep levels in the whole energy range of the band gap of 4H–SiC by deep level transient spectroscopy. The deep levels are generated by ion implantation. The dominant defects in n-type samples after ion implantation and high-temperature annealing at 1700 °C are IN3 (Z1/2: EC-0.63 eV) and IN9 (EH6/7: EC-1.5 eV) in low-dose-implanted samples, and IN8 (EC-1.2 eV) in high-dose-implanted samples. These defects can remarkably be reduced by thermal oxidation at 1150 °C. In p-type samples, however, IP8 (HK4: EV+1.4 eV) survives and additional defects such as IP4 (HK0: EV+0.72 eV) appear after thermal oxidation in low-dose-implanted samples. In high-dose-implanted p-type samples, three dominant levels, IP5 (HK2: EV+0.85 eV), IP6 (EV+1.0 eV), and IP7 (HK3: EV+1.3 eV), are remarkably reduced by oxidation at 1150 °C. The dominant defect IP4 observed in p-type 4H–SiC after thermal oxidation can be reduced by subsequent annealing in Ar at 1400 °C. These phenomena are explained by a model that excess interstitials are generated at the oxidizing interface, which diffuse into the bulk region. [ABSTRACT FROM AUTHOR]

In this study, the authors investigate deep levels, which are induced by reactive ion etching (RIE) of n-type/p-type 4H–SiC, by deep level transient spectroscopy (DLTS). The capacitance of a Schottky contact fabricated on as-etched p-type SiC is abnormally small due to compensation or deactivation of acceptors extending to a depth of ∼14 μm, which is nearly equal to the epilayer thickness. The value of the capacitance can recover to that of a Schottky contact on as-grown samples after annealing at 1000 °C. However, various kinds of defects, IN2 (EC-0.30 eV), EN (EC-1.6 eV), IP1 (EV+0.30 eV), IP2 (EV+0.39 eV), IP4 (HK0: EV+0.72 eV), IP5 (EV+0.85 eV), IP7 (EV+1.3 eV), and EP (EV+1.4 eV), remain at a high concentration (average of total defect concentration in the region ranging from 0.3 μm to 1.0 μm:∼5×1014 cm-3) even after annealing at 1000 °C. The concentration of all these defects generated by RIE, except for the IP4 (HK0) center, remarkably decreases by thermal oxidation. In addition, the HK0 center can also be reduced significantly by a subsequent annealing at 1400 °C in Ar. [ABSTRACT FROM AUTHOR]

The authors investigated deep levels in the whole energy range of bandgap of 4H-SiC, which are generated by low-dose N+, P+, and Al+ implantation, by deep level transient spectroscopy (DLTS). Ne+-implanted samples have been also prepared to investigate the pure implantation damage. In the n-type as-grown material, the Z1/2 (EC-0.63 eV) and EH6/7 (EC-1.6 eV) centers are dominant deep levels. At least, seven peaks (IN1, IN3–IN6, IN8, and IN9) have emerged by implantation and annealing at 1000 °C in the DLTS spectra from all n-type samples, irrespective of the implanted species. After high-temperature annealing at 1700 °C, however, most DLTS peaks disappeared, and two peaks, IN3 and IN9, which may be assigned to Z1/2 and EH6/7, respectively, survive with a high concentration over the implanted atom concentration. In the p-type as-grown material, the D (EV+0.40 eV) and HK4 (EV+1.4 eV) centers are dominant. Two peaks (IP1 and IP3) have emerged by implantation and annealing at 1000 °C, and four traps IP2 (EV+0.39 eV), IP4 (EV+0.72 eV), IP7 (EV+1.3 eV), and IP8 (EV+1.4 eV) are dominant after annealing at 1700 °C in all p-type samples. The IP2 and IP8 may be assigned to the HS1 and HK4 centers, respectively. The depth analyses have revealed that the major deep levels are generated in the much deeper region than the implant profile. [ABSTRACT FROM AUTHOR]

The Z1/2 center in n-type 4H-SiC epilayers-a dominant deep level limiting the carrier lifetime-has been investigated. Using capacitance versus voltage (C-V) measurements and deep level transient spectroscopy (DLTS), we show that the Z1/2 center is responsible for the carrier compensation in n-type 4H-SiC epilayers irradiated by low-energy (250 keV) electrons. The concentration of the Z1/2 defect obtained by C-V and DLTS correlates well with that of the carbon vacancy (VC) determined by electron paramagnetic resonance, suggesting that the Z1/2 deep level originates from VC. [ABSTRACT FROM AUTHOR]