Abstract
An avalanche photodiode has internal gain, so that it has high sensitivity and is suitable for long-haul fiber communication system. The layer structure is a SACM (separate absorption, charge and multiplication) configuration. The multiplication layer is a 28 -pairs of InAlGaAs/InAlAs supperlattice structure, which was grown by MOCVD. And the supperlattice structure can enhance the difference between the ionization coefficient of electrons and holes further improves the performance. According to the calculation, the minimum field of multiplication layer must be above 5 105V/cm, and the maximum field of absorption layer should below 2 105V/cm. The mesa SL-APD was successfully formed by wet etching, and the mesa diameter is 50um. The breakdown voltage is about 33.2 voltage; 0.95 VB, the dark current is anout 1uA, the gain is 13, and the capacitance is about 1.6 pF.