GaAlAs Sb APD optimization

It has been demonstrated that avalanche gain can be obtained in GaAlSb avalanche photodiodes which exhibit ionization coefficient enhancement. These devices exhibit gain at relatively high impurity background density of 8-9 x 10 to the 15th power/cu cm. This indicates that a tunneling process which occurs in these devices is associated with a deep level rather than a band-to-band process. Surface leakage current, which dominates the total dark current of these avalanche photodiodes at room temperature, can be reduced with the use of special structures. However, as shown in this work through both modeling and experiment, defect assisted tunneling may be a fundamental limitation to obtaining high sensitivity devices. Finally, a serious problem from the manufacturing standpoint is the necessity to compensate the native defect that results in a high concentration of intrinsic p-type acceptor levels. Precise control of dopant incorporation is required to reproducibly obtain the required net impurity levels. This is an extremely difficult process with the available LPE GaAlSb materials technology.