Light-receiving device and method for producing the same

Abstract

A light-receiving device includes a light-receiving layer having an undoped multi-quantum well structure; a cap layer disposed on the light-receiving layer, the cap layer including a semiconductor layer doped with a p-type impurity; a mesa structure including the cap layer; a p-type region extending from the p-type semiconductor layer toward the light-receiving layer, the p-type region including the p-type impurity diffused from the semiconductor layer in the mesa structure; a p-n junction formed at an end of the p-type region; and an electrode disposed on the cap layer of the mesa structure. The mesa structure is defined by a trench surrounding the mesa. The trench has a bottom that reaches the vicinity of an upper surface of the light-receiving layer. The p-n junction is located in the light-receiving layer or at the boundary between the light-receiving layer and the cap layer disposed on the light-receiving layer.

What is claimed is: 
     
         1 . A light-receiving device comprising:
 a light-receiving layer disposed on a substrate, the light-receiving layer having an undoped multi-quantum well structure;   a cap layer disposed on the light-receiving layer, the cap layer including a p-type semiconductor layer doped with a p-type impurity;   a mesa structure disposed on the substrate, the mesa structure including the cap layer;   a p-type region extending from the p-type semiconductor layer toward the light-receiving layer, the p-type region including the p-type impurity diffused from the p-type semiconductor layer in the cap layer in the mesa structure;   a p-n junction formed at an end of the p-type region; and   an electrode disposed on the cap layer of the mesa structure,   wherein the mesa structure is defined by a trench surrounding the mesa,   the trench has a bottom that reaches the vicinity of an upper surface of the light-receiving layer, and   the p-n junction is located in the light-receiving layer or at the boundary between the light-receiving layer and the cap layer disposed on the light-receiving layer.   
     
     
         2 . The light-receiving device according to  claim 1 , wherein the cap layer includes a p-type contact layer doped with the p-type impurity and a concentration adjusting layer, the concentration adjusting layer being not doped or being doped with a lower concentration of an impurity than the p-type contact layer,
 the concentration adjusting layer is disposed between the p-type contact layer and the light-receiving layer, and   the electrode is disposed on the p-type contact layer.   
     
     
         3 . The light-receiving device according to  claim 2 , wherein the p-type contact layer is formed of one selected from an InGaAs layer and an InP layer. 
     
     
         4 . The light-receiving device according to  claim 2 , wherein the concentration adjusting layer is formed of at least one selected from an InGaAs layer and an InP layer. 
     
     
         5 . The light-receiving device according to  claim 1 , wherein the p-type region has a concentration of the p-type impurity of 5×10 16  cm −3  or less at the boundary between the light-receiving layer and the cap layer disposed on the light-receiving layer. 
     
     
         6 . The light-receiving device according to  claim 1 , wherein the light-receiving layer includes an undoped type-II multi-quantum well structure. 
     
     
         7 . The light-receiving device according to  claim 6 , wherein the substrate is made of InP, and
 the type-II multi-quantum well structure of the light-receiving layer includes InGaAs layers and GaAsSb layers alternately stacked.   
     
     
         8 . The light-receiving device according to  claim 6 , wherein the type-II multi-quantum well structure of the light-receiving layer includes GaSb layers and InAs layers alternately stacked. 
     
     
         9 . A method for producing a light-receiving device, the method comprising the steps of:
 growing a light-receiving layer on a substrate, the light-receiving layer having an undoped multi-quantum well structure;   growing a cap layer on the light-receiving layer, the cap layer including a p-type semiconductor layer doped with a p-type impurity;   forming a mesa structure by etching the cap layer, the mesa structure being defined by a trench surrounding the mesa;   after the step of forming the mesa structure, forming a protective film on an upper surface and a side surface of the mesa structure; and   after the step of forming the protective film, forming a p-n junction in the light-receiving layer or at the boundary between the light-receiving layer and the cap layer by annealing with the upper surface and the side surface of the mesa structure covered with the protective film at a predetermined temperature,   wherein, in the step of forming the mesa structure, the trench reaches the vicinity of an upper surface of the light-receiving layer, and   in the step of forming the p-n junction, the p-type impurity in the p-type semiconductor layer is diffused from the cap layer in the mesa structure to the light-receiving layer.   
     
     
         10 . The method according to  claim 9 , wherein the cap layer includes a concentration adjusting layer formed on the light-receiving layer and a p-type contact layer formed on the concentration adjusting layer, the p-type contact layer being doped with the p-type impurity,
 the concentration adjusting layer is not doped or is doped with a p-type or an n-type impurity at a lower concentration than that of the p-type contact layer, and   in the step of forming the p-n junction, the p-type impurity is diffused from the p-type contact layer in the mesa structure to the light-receiving layer through the concentration adjusting layer.   
     
     
         11 . The method according to  claim 9 , wherein, in the step of growing the cap layer, the p-type semiconductor layer in the cap layer is grown while the p-type impurity is doped with a concentration gradually or stepwise increased with the lapse of growth time from the beginning of the growth. 
     
     
         12 . The method according to  claim 9 , wherein the light-receiving layer and the cap layer are grown at a growth temperature of 425° C. to 575° C. by a metal-organic vapor phase epitaxy method using metal-organic compounds for a III group source material and a V group source material. 
     
     
         13 . The method according to  claim 9 , wherein the light-receiving layer includes an undoped type-II multi-quantum well structure. 
     
     
         14 . A method for producing a light-receiving device, the method comprising the steps of:
 growing a light-receiving layer on a substrate, the light-receiving layer having an undoped multi-quantum well structure;   forming a selective growth mask on the light-receiving layer, the selective growth mask including an opening through which the light-receiving layer is exposed;   selectively growing a concentration adjusting layer and a p-type contact layer, in that order, on the light-receiving layer using the selective growth mask, the p-type contact layer being doped with a p-type impurity; and   forming a p-n junction in the light-receiving layer or at the boundary between the light-receiving layer and the concentration adjusting layer,   wherein the concentration adjusting layer is not doped or is doped with a p-type or an n-type impurity at a lower concentration than that of the p-type contact layer, and   in the step of forming the p-n junction, the p-type impurity doped in the p-type contact layer is diffused to the light-receiving layer through the concentration adjusting layer during growing the p-type contact layer.