This is the ideal reverse current which is always constant whatever the voltage is. If you put some defects then you get changing current. Your program is working OK. if you want to simulate a photodetector then you should put some light. Good luck

thank you for your response. yes that's true so but how to define light here from the right side instead of coming on the top in silvaco

yes but I need to define light location which is from the right side with angle 180 but I do not know how