PERFORMANCE OF THIN SEPARATE ABSORPTION, CHARGE, AND MULTIPLICATION AVALANCHE PHOTODIODES

Previously, it has been demonstrated that resonant-cavity-enhanced sep arate-absorption-and-multiplication (SAM) avalanche photodiodes (APD's ) can achieve high bandwidths and high gain-bandwidth products while m aintaining good quantum efficiency, In this paper, we describe a GaAs- based resonant-cavity-enhanced SAM APD that utilizes a thin charge lay er for improved control of the electric field profile, These devices h ave shown RC-limited bandwidths above 30 GHz at low gains and gain-ban dwidth products as high as 290 GHz. In order to gain insight into the performance of these APD's, homojunction APD's with thin multiplicatio n regions were studied, It was found that the gain and noise have a de pendence on the width of the multiplication region that is not predict ed by conventional models. Calculations using width-dependent ionizati on coefficients provide good fits to the measured results, These calcu lations indicate that the gain-bandwidth product depends strongly on t he charge layer doping and on the multiplication layer thickness and, further, that even higher gain-bandwidth products can be achieved with optimized structures.