Cross‐Sectional Carrier Lifetime Profiling and Deep Level Monitoring in Silicon Carbide Films Exhibiting Variable Carbon Vacancy Concentrations

Abstract

The carrier lifetime control over 150 μm thick 4H‐SiC epitaxial layers via thermal generation and annihilation of carbon vacancy (VC) related Z1/2 lifetime killer sites is reported. The defect developments upon typical SiC processing steps, such as high‐ and moderate‐temperature anneals in the presence of a carbon cap, are monitored by combining electrical characterization techniques capable of VC depth‐profiling, capacitance–voltage (CV) and deep‐level transient spectroscopy (DLTS), with a novel all‐optical approach of cross‐sectional carrier lifetime profiling across 4H‐SiC epilayer/substrate based on imaging time‐resolved photoluminescence (TRPL) spectroscopy in orthogonal pump‐probe geometry, which readily exposes in‐depth efficacy of defect reduction and surface recombination effects. The lifetime control is realized by initial high‐temperature treatment (1800 °C) to increase VC concentration to ≈1013 cm−3 level followed by a moderate‐temperature (1500 °C) post‐annealing of variable duration under C‐rich thermodynamic equilibrium conditions. The post‐annealing carried out for 5 h in effect eliminates VC throughout the entire ultra‐thick epilayer. The reduction of VC‐related Z1/2 sites is proven by a significant lifetime increase from 0.8 to 2.5 μs. The upper limit of lifetimes in terms of carrier surface leakage and the presence of other nonradiative recombination centers besides Z1/2, possibly related to residual impurities such as boron are discussed.