Optimization of 4H-SiC separated-absorption-charge-multiplication (SACM) avalanche photodiode with low avalanche breakdown voltage

4H-SiC avalanche photodiode with a separated absorption region, a charge adjustment region and a multiplication region is proposed and its optoelectronic performance is modeled. By properly designing the doping concentration of each layer, the avalanche breakdown voltage and photo-response of the device is found to be dependent of the thickness of the multiplication region. The avalanche breakdown voltage shows a minimum and the photo-response shows a maximum at certain thickness of the multiplication region. The results are explained by the electric field distribution of the device and the impact ionization theory.