Numerical Calculation of the Evolution of the Carrier Distribution in the Spatially Modulated Light CMOS Detector

Abstract—The Spatially Modulated Light CMOS detector (SML CMOS detector) removes the slow part of the current response of a traditional CMOS photodetector, by using the difference between the signals of an immediate and a deferred detector. This slow part of the current response limits the maximum frequency of a photodetector in the conventional CMOS technology to a few MHz. Experimental evidence shows that the SML CMOS detector operates beyond the GHz range, and this using commercially available CMOS technology. However, no theoretical work has been published up to now, indicating the real frequency limits of the SML CMOS detector. In this work, we solved numerically the minoritycarrier diffusion equation in two dimensions with border conditions specific to the SML CMOS detector. A short pulse of incident light is applied and then the current response of the detector is extracted from the simulation results. This current response is compared with the response of a traditional CMOS photodetector, showing the superior characteristics of the SML detector. Next, the simulated current response is compared with the experimental current response, which shows an excellent correspondence. Therefore, we conclude that the SMLdetector is the solution of choice for cheap, CMOScompatible receivers in integrated opto-electronic systems.