Simulation Of Light-Activated SiC-based Power Devices

Photoelectric characteristics of SiCGe/SiC heterojunction diode were simulated using MEDICI tools, and the simulation results are presented and discussed in this paper. The abrupt heterojunction diode is composed of a 1 m thick heavily doped n-type SiC layer and a 0.4 m thick lightly doped p-type SiC1-xGex layer with varied composition ratios. It has been shown that photocurrent of the pn+ SiC1-xGex/SiC diode does not decrease apparently by changing the composition ratio from 0.2 to 0.3 for the applied reverse-bias voltage of 3V and the incident light intensity of 0.23 Watts/cm2. Corresponding photocurrents of the diodes are 7.765 10-7A/ m and 7.438 10-7A/urn, and the longest wavelength limits are 0.64 m and 0.70 m, respectively. It has also been shown by the simulation results that p-i-n structure composed by adding a p+-SiC1-xGex thin layer on top of the lightly doped p-type SiC1-xGex layer is much better for obtaining a higher photocurrent. Under the same conditions, photocurrents of 1.6734 10-6A/um and 1.844 10-6A/ m can be obtained in the p-i-n SiC1-xGex/SiC diodes with x = 0.2 and 0.3, respectively.To eliminate the EMI problem of the SiC-Darlington transistor, a novel light-activated SiC-Darlington device is presented. It is accomplished that a SiC-Darlington transistor and a SiCGe/SiC heterojunction photodiode employed to produce a base current to trigger the former are monolithically integrated. When the blocking voltage Vce between the Collector and the Emitter electrodes of the SiC Darlington is 100V and the base current is about 1 10-7A/um, the output current approximately amounts to 10-4 A/ m with the peak current gain of more than 1000. By means of appropriate design, the output photocurrent of the SiCGe/SiC heterojunction photodiode can reach l 10-7A/ m large enough to make the SiC Darlington transistor operate in an optimal status. Then it is obtained that the idea of the novel light-activated device is feasible.