Prolonging Carrier Lifetime in P-type 4H-SiC Epilayer by Thermal Oxidation and Hydrogen Annealing

TL;DR

This study demonstrates that combining thermal oxidation with hydrogen annealing significantly prolongs minority carrier lifetime in P-type 4H-SiC epilayers by reducing carbon vacancies and defects, improving device performance.

Contribution

It introduces a novel process sequence of thermal oxidation followed by hydrogen annealing to effectively eliminate carbon vacancies in 4H-SiC epilayers.

Findings

Carrier lifetime reached 25.46 μs in the treated epilayer.

Hydrogen annealing reduces stacking faults and dislocation density.

Carbon vacancy defects are significantly decreased after hydrogen treatment.

Abstract

A minority carrier lifetime of 25.46 $\mu$s in a P-type 4H-SiC epilayer has been attained through sequential thermal oxidation and hydrogen annealing. Thermal oxidation can enhance the minority carrier lifetime in the 4H-SiC epilayer by reducing carbon vacancies. However, this process also generates carbon clusters with limited diffusivity and contributes to the enlargement of surface pits on the 4H-SiC. High-temperature hydrogen annealing effectively reduces stacking fault and dislocation density. Moreover, electron spin resonance analysis indicates a significant reduction in carbon vacancy defects after hydrogen annealing. The mechanisms of the elimination of carbon vacancies by hydrogen annealing include the decomposition of carbon clusters formed during thermal oxidation and the low-pressure selective etching by hydrogen, which increases the carbon content on the 4H-SiC surface and facilitates carbon diffusion. Consequently, the combination of thermal oxidation and hydrogen annealing eliminates carbon vacancies more effectively, substantially enhancing the minority carrier lifetime in P-type 4H-SiC. This improvement is advantageous for the application of high-voltage SiC bipolar devices.