Electrically active defects induced by thermal oxidation and post-oxidation annealing of n-type 4H-SiC

Abstract

In this work, we have performed a detailed study of the defects created in the bulk of 4H-SiC after thermal oxidation and post oxidation annealing using deep level transient spectroscopy and minority carrier transient spectroscopy (MCTS). The study reveals the formation of several shallow and deep level majority carrier traps in the bandgap. The ON1 (EC−0.85 eV), ON2a (EC−1.05 eV), and ON2b (Ec−1.17 eV) levels are the most dominant and are observed across all the samples (EC denotes the conduction band edge). Three shallow levels Ti(k) (EC−0.17 eV), E0.23 (EC−0.23 eV), and C1/2 (EC−0.36/0.39 eV) are observed in the samples. For most of the majority carrier defects, the highest concentration is observed after an NO anneal at 1300°C. This behavior is sustained in the depth profile measurements where the defect concentration after the NO anneal at 1300°C is significantly higher than for the rest of the samples. The origin of most of the majority carrier defects has been attributed to C interstitial injection from the interface during thermal oxidation and annealing. MCTS measurements reveal two prominent minority carrier traps, labeled O0.17 (EV+0.17 eV) and B (EV+0.28 eV), where the concentration of O0.17 is independent of annealing parameters while the concentration of the B level increases after the NO anneal (EV denotes the valence band edge). Furthermore, the depth profiles of the defects are used to evaluate their diffusion parameters by solving the diffusion equation to fit the experimental profiles. The defect concentrations decay exponentially with depth, which evidences that the defects were created at or near the SiO2–SiC interface and migrate toward the bulk during oxidation and post-oxidation annealing.