Charge-layer design considerations in SAGCM InGaAs/InAlAs avalanche photodiodes

We report on the development of mesa-processed InGaAs/InAlAs avalanche photodiodes (APDs) for short-wave infrared (SWIR) imaging applications with demand for high gain and low breakdown voltage. Devices are designed with separate absorption, grading, charge, and multiplication (SAGCM) layers. Special attention has been paid to the charge layer in order to optimize the structure for low band discontinuities and an appropriate electric field distribution. Hereof, a combination of a p-type grading layer and charge layer is presented. Band-edge profile calculations as well as electro-optical characterization results of the APDs will be discussed in this article. Our optimized APD structures reveal low punch-through and low breakdown voltage of V-pt approximate to 8.5 V and V-bd approximate to 2.3 V, respectively. A maximum gain of M > 300 in the linear operation mode is demonstrated at room temperature and M = 10 has been measured at 20 V bias.