Avalanche Photo Diode

Abstract

An avalanche photodiode including a first electrode; and a substrate including a first semiconductor layer of a first conduction type electrically connected to the first electrode, in which at least an avalanche multiplication layer, a light absorption layer, and a second semiconductor layer of a second conduction type with a larger band gap than the light absorption layer are deposited on the substrate. The second semiconductor layer is separated into inner and outer regions by a groove formed therein, the inner region electrically connected to a second. With the configuration, the avalanche photodiode has a low dark current and high long-term reliability. In addition, the outer region includes an outer trench, and at least the light absorption layer is removed by the outer trench to form a side face of the light absorption layer. With the configuration, the dark current can be further reduced.

1 . An avalanche photodiode comprising:
 a first electrode; and   a substrate including a first semiconductor layer made of a first conduction type electrically connected to the first electrode,   wherein at least an avalanche multiplication layer, a light absorption layer, and a second semiconductor layer made of a second conduction type with a larger band gap than the light absorption layer are deposited on the substrate,   wherein the second semiconductor layer is separated into an inner region and an outer region by a groove formed therein, and   wherein the inner region is electrically connected to a second electrode.   
   
   
       2 . The avalanche photodiode according to  claim 1 , wherein a third semiconductor layer with a larger band gap than the light absorption layer is formed between the light absorption layer and the second semiconductor layer, and the groove is formed by leaving the third semiconductor layer. 
   
   
       3 . The avalanche photodiode according to  claim 1 , wherein the outer region is provided with an outer trench to surround the inner region and the groove, and at least the light absorption layer is removed by the outer trench to form a side face thereof. 
   
   
       4 . The avalanche photodiode according to  claim 3 , wherein the outer trench reaches a cleavage plane of the substrate. 
   
   
       5 . The avalanche photodiode according to  claim 3 , wherein the outer trench and the groove are formed continuously. 
   
   
       6 . The avalanche photodiode according to  claim 1 , wherein the second semiconductor layer in the inner region has a plurality of layers, and widths of the plurality of layers increase as they get closer to the substrate. 
   
   
       7 . The avalanche photodiode according to  claim 1 , wherein the second semiconductor layer in the inner region has a plurality of layers, and mobilities of the plurality of layers decrease as they get closer to the substrate. 
   
   
       8 . The avalanche photodiode according to  claim 1 , wherein a light incidence portion is any one of a front-surface incident type of a front surface of the substrate, a back-surface incident type of a back surface of the substrate, and a side-surface incident type of a side wall formed by the groove or the outer trench.