Temperature dependence of hole impact ionization coefficients in 4H and 6H-SiC

Hole impact ionization coefficients have been accurately measured as a func tion of temperature in both 4H and 6H-SiC using the pulsed electron beam in duced current (P-EBIC) technique. For Chynoweth's equation (alpha = a e(-b) /E), our measurements gave an a(p) value of (2.6 +/- 0.12) x 10(6)/cm and a b(p) value of (1.5 +/- 0.01) x 10(7) V/cm for 6H-SiC at room temperature w hile the values of a(p) and b(p) for 4H-SiC were found to be (3.25 +/- 0.3) x 10(6)/cm and (1.71 +/- 0.01) x 10(7) V/cm, respectively, at room tempera ture. The coefficient a(p) was found to decrease with increasing temperatur e for both polytypes while the coefficient b(p) remained constant, Based up on this data, the breakdown voltage of the 4H and GH-SIC devices is predict ed to increase with temperature which is an important desirable characteris tic for power devices. (C) 1998 Elsevier Science Ltd. All rights reserved.