Reduction of Deep Levels and Improvement of Carrier Lifetime in n-Type 4H-SiC by Thermal Oxidation

Significant reduction of major deep levels in n-type 4H-SiC(0001) epilayers by means of thermal oxidation is demonstrated. By thermal oxidation of epilayers at 1150–1300 °C, the concentration of the Z1/2 and EH6/7 centers has been reduced from (0.3–2)×1013 cm-3 to below the detection limit (1×1011 cm-3). The depth-profile analysis of the Z1/2 center has revealed that the Z1/2 center is eliminated to a depth of about 50 µm from the surface after thermal oxidation at 1300 °C for 5 h. The carrier lifetime in an n-type 4H-SiC epilayer measured by differential microwave photoconductance decay has been significantly improved from 0.73 µs (as-grown) to 1.62 µs (after oxidation: 1300 °C, 5 h×2). The reduction mechanism of the Z1/2 and EH6/7 centers is discussed.