Semiconductor photo-detector having a two-stepped impurity profile

Claim 2

A semiconductor photodetector comprising: a semiconductor substrate; a light absorption layer of a first conductivity type formed on the semiconductor or substrate; a multiplication layer of said first conductivity type, formed on the light absorption layer, for multiplying a photocurrent; a semiconductor region of a second conductivity type formed on the multiplication layer and constituting an abrupt pn junction with said multiplication layer; and a guard ring area of a second conductivity type formed around a periphery of the semiconductor region such that a carrier concentration profile of said guard ring area has a large gradient portion at a location adjacent to a device surface and a small gradient portion below the large gradient portion, said small gradient portion having substantially constant carrier concentration and at least reaching to a pn junction between said guard ring area and an adjacent layer; wherein the carrier concentration gradient of said large gradient portion is above 3 decade/μm, and the carrier concentration gradient of said small gradient portion is below 0.2 decade/μm, and the unit decade/μm is defined as the exponent to the base 10 of the carrier concentration in atom/cm 3 per μm of depth in said guard ring area.

Claim 3

A semiconductor photo-detector according to claim 1, wherein a buried layer is provided around said multiplication layer, an impurity concentration level of said multiplication layer is 1×10 16 to 1×10 17 atom/cm 3 , said buried layer has an impurity concentration level of 1×10 15 to ×10 16 atom/cm 3 , and an impurity of said second conductivity type comprises magnesium.

Claim 4

A semiconductor photo-detector according to claim 1, wherein a pn junction defined between said multiplication layer and said semiconductor region is an abrupt type and a pn junction formed in said guard ring area is a graded type.

Claim 5

A semiconductor photo-detector according to claim 1, wherein a pn junction defined between said multiplication layer and said semiconductor region is of an abrupt type and an inner portion of a side area of said guard ring area constitutes a low concentration layer.

Claim 6

A semiconductor photo-detector comprising: a semiconductor substrate; a light absorption layer of a first conductivity type formed on the semiconductor substrate; a multiplication layer of said first conductivity type, formed on the light absorption layer, for multiplying a photocurrent; a semiconductor region of a second conductivity type formed on the multiplication layer and constituting an abrupt pn junction with said multiplication layer; and a guard ring area of a second conductivity type formed around a periphery of the semiconductor region such that a carrier concentration profile of said guard ring area has a large gradient portion at a location adjacent to a device surface and a small gradient portion below the large gradient portion, said small gradient portion having substantially constant carrier concentration, and at least reaching to a p-n junction between said guard ring area and an adjacent layer; wherein said multiplication layer is InP and said guard ring area is formed by a magnesium ion implantation; and wherein the carrier concentration gradient of said large gradient portion is above 3 decade/μm, and the carrier concentration gradient of said small gradient portion is below 0.2 decade/μm, and the unit decade/μm is defined as the exponent to the base 10 of the carrier concentration in atom/cm 3 per μm of depth in said guard ring area.

Claim 7

A semiconductor photo-detector comprising: a semiconductor substrate; a light absorption layer of a first conductivity type formed on the semiconductor substrate; a multiplication layer of said first conductivity type, formed on the light absorption layer, for multiplying a photocurrent; a semiconductor region of a second conductivity type formed on the multiplication layer and constituting an abrupt pn junction with said multiplication layer; and a guard ring area of a second conductivity type formed around a periphery of the semiconductor region such that a carrier concentration profile of said guard ring area has a large gradient portion at a location adjacent to a device surface and a small gradient portion below the large gradient portion, said small gradient portion having substantially constant carrier concentration, and at least reaching to a p-n junction between said guard ring area and an adjacent layer; wherein said multiplication layer is InP and said guard ring area is formed by a magnesium ion implantation; and wherein the carrier concentration gradient of said large gradient portion is above 3 decade/μm, and the carrier concentration gradient of said small gradient portion is below 0.2 decade/μm, and the unit decade/μm is defined as the exponent to the base 10 of the carrier concentration in atom/cm 3 per μm of depth in said guard ring area.