Experimental investigation of the charge-layer doping level in InGaAs/InAlAs avalanche photodiodes

We report on the development of mesa-processed InGaAs/InAlAs avalanche photodiodes (APDs) for short-wave infrared (SWIR) 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 distribution of the electric field across the device. Since the device performance significantly changes for deviations of only several percent in the doping concentration a series with variation of the charge-layer doping level has been carried out. 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 a low dark-current density of Id=1×10-4 A/cm2 at gain M=10 and a low breakdown voltage Vbd<30V. A maximum gain larger than 300 in the linear operation mode is demonstrated at room temperature as well as 140 K.