Avalanche Multiplication and Time in Thin 4H-SiC Avalanche Photodiodes

A Monte Carlo model using random ionization path lengths describing the gain, excess noise, and time for different groups of carriers in thin 4H-SiC avalanche photodiodes (APDs) is developed. This work simulated the mean multiplication gain and excess noise of electrons and holes in 4H-SiC APDs at 0.05 µm, 0.1 µm, 0.2 µm and 0.3 µm multiplication widths in a high electric field and computed avalanche time at 0.1 μm and 0.2 µm in detail for both electron- and hole-initiated multiplication with dead space. The model simulates higher hole impact ionization coefficients than those of electrons for an electric field below 2 MV/cm. Our results show that hole-initiated multiplication gives higher gain and possesses lower excess noise than electron-initiated multiplication. The avalanche time of carriers increases with the width of the multiplication region. Longer avalanche time in a thin device may limit the performance of an APD as an optical signal sensing device. Our model shows the distribution of carriers with respect to time in detail, inclusive of the existence of secondary carriers due to different groups of feedback carriers and dead time. The hole-initiated multiplication shows faster avalanche time than electron-initiated multiplication due to the fast feedback electrons.