Numerical Simulation And Analysis Of Characteristics For SiCGe/SiC Hetero-junction Photodiode

For the purpose of developing a light-triggering SiC power switch, characteristics of the SiCGe/SiC hetero-junction photodiode are simulated and analyzed using MEDICI. In this thesis, a method to decide the Ge composition in SiCGe alloy is presented, which can absorb visible or near infrared light under the limitation of lattice mismatch between SiCGe and 6H-SiC. Optoelectronic properties of the SiCGe/SiC hetero-j unction photodiode with proper process parameter are also presented and discussed based on the computer aided design of device and process parameters and the characteristics simulations, in which some physical models of SiC were used for the new material SiCGe.It has been shown in the simulation that the parameter choices of either lifetime and mobility in p-SiCGe layer or lifetime in 6H-SiC layer have less effect upon optical responsibility of the photodiode, which is well dependant on the doping concentration because of the concentration dependence of the depletion layer width. As parameters of the n-type 6H-SiC layer are determined in design of the main device, effect of the thickness and the doping concentration on the optical responsibility is emphasized only for the p-type SiCGe layer. Simulation results show that for a high enough optical responsibility the SiCGe with Ge composition ratio x of 0.3 can get a lower lattice mismatch of 0.085 with 6H-SiC in (0001) face, and the corresponding responsibility of the SiCGe/SiC is about 150mA/W to the light of 0.63 μm wavelength. This work also indicates that PIN structure is better than PN structure one in responsibility. The responsibility of a SiCGe/SiC heteroj unction PIN-type photodiode which consists of SiCGe P+and P*layers with doping concentration of 5 x 1018cm"3 and 1xl015cm'3, thickness of 0.6 μm and 1.6 μm, respectively raise to 185mA/W to the same 0.63μm light. Therefore, it is suggested that the optical control cell of the light-triggering SiC power switch under development is better designed as a SiCGe/SiC PIN hetero-j unction photodiode.