Avalanche photodiodes

Claim 2

An avalanche photodiode comprising:- a light absorbing layer, of a semiconductor containing at least one impurity of one conductivity type, an active layer, of a semiconductor having a larger band gap than that of the semiconductor of the light absorbing layer, containing at least one impurity of the said one conductivity type, and a further layer, between the light absorbing layer and the active layer or upon the active layer with the active layer upon the light absorbing layer, of a semiconductor having a larger band gap than that of the semiconductor of the light absorbing layer, containing at least one impurity of the said one conductivity type, the photodiode having a p-n junction at least one part of which is located in the active layer, to provide a light sensitive region, and other parts of which are more remote than the said one part from the light absorbing layer.

Claim 3

An avalanche photodiode comprising:- a light absorbing layer, of a semiconductor containing at least one impurity of one conductivity type, a middle layer, of a semiconductor providing lattice matching between itself and the light absorbing layer and having a larger band gap than that of the semiconductor of the light absorbing layer, the middle layer being formed on the light absorbing layer, and containing at least one impurity of the said one conductivity type, and an active layer, of a semiconductor providing lattice matching between itself and the middle layer, having a larger band gap than the semiconductor of the light absorbing layer, the active layer being formed on the middle layer and primarily containing at least one impurity of the said one conductivity type, in a concentration less than that of the middle layer, but having a region therein which contains at least one impurity of a conductivity type opposite to the said one conductivity type to provide a light sensitive region separated from other regions of the active layer by a p-n junction which, surrounding the light sensitive region, has gradually inclined parts.

Claim 4

An avalanche photodiode comprising:- a light absorbing layer, of a semiconductor containing at least one impurity of one conductivity type, a middle layer, of a semiconductor providing lattice matching between itself and the light absorbing layer and having a larger band gap than that of the semiconductor of the light absorbing layer, the middle layer being formed on the light absorbing layer, and containing at least one impurity of the said one conductivity type, and an active layer, of a semiconductor providing lattice matching between itself and the middle layer, having a larger band gap than the semiconductor of the light absorbing layer, the active layer being formed on the middle layer and primarily containing at least one impurity of the said one conductivity type, in a concentration less than that of the middle layer, but having a region therein which contains at least one impurity of a conductivity type opposite to the said one conductivity type to provide a light sensitive region separated from other regions of the active layer by a p-n junction which, surrounding the light sensitive region, has gradually inclined parts.

Claim 5

An avalanche photodiode comprising:- a light absorbing layer, of a semiconductor containing at least one impurity of one conductivity type, a middle layer, of a semiconductor providing lattice matching between itself and the light absorbing layer and having a larger band gap than that of the semiconductor of the light absorbing layer, the middle layer being formed on the light absorbing layer and containing at least one impurity of the said one conductivity type, and an active layer, of a semiconductor providing lattice matching between itself and the middle layer, having a larger band gap than the semiconductor of the light absorbing layer, the active layer being formed on the middle layer and primarily containing at least one impurity of the said one conductivity type, in a concentration less than that of the middle layer, but having a region therein which contains at least one impurity of a conductivity type opposite to the said one conductivity type to provide a light sensitive region separated from other regions of the active layer by a step shaped p-n junction having a relatively deep part which faces the light sensitive region and a relatively shallow part which surrounds the relatively deep part, and an abrupt transitional part between the relatively deep and relatively shallow parts.

Claim 6

An avalanche photodiode comprising:- a light absorbing layer, of a semiconductor containing at least one impurity of one conductivity type, a middle layer, of a semiconductor providing lattice matching between itself and the light absorbing layer and having a larger band gap than that of the semiconductor of the light absorbing layer, the middle layer being formed on the light absorbing layer and containing at least one impurity of the said one conductivity type, and an active layer, of a semiconductor providing lattice matching between itself and the middle layer, having a larger band gap than the semiconductor of the light absorbing layer, the active layer being formed on the middle layer and primarily containing at least one impurity of the said one conductivity type, in a concentration less than that of the middle layer, but having a region therein which contains at least one impurity of a conductivity type opposite to the said one conductivity type to provide a light sensitive region separated from other regions of the active layer by a step shaped p-n junction having a relatively deep part which faces the light sensitive region and a relatively shallow part which surrounds the relatively deep part, and an abrupt transitional part between the relatively deep and relatively shallow parts.

Claim 7

An avalanche photodiode comprising:- a light absorbing layer, of a semiconductor containing at least one impurity of one conductivity type, an active layer, of a semiconductor providing lattice matching between itself and the light absorbing layer and having a larger band gap than that of the semiconductor of the light absorbing layer, the active layer being formed on the light absorbing layer and primarily containing at least one impurity of the said one conductivity type, and a surface layer, of a semiconductor providing lattice matching between itself and the active layer and having a larger band gap than that of the semiconductor of the light absorbing layer, the surface layer being formed on the active layer and primarily containing at least one impurity of the said one conductivity type, in a concentration less than that of the active layer, but the surface layer and an upper portion of the active layer having therein a region which contains at least one impurity of a conductivity type opposite to the said one conductivity type to provide a light sensitive region separated from other regions of the surface layer and the active layer by a well shaped p-n junction of which the bottom is located in the active layer.

Claim 8

An avalanche photodiode comprising:- a light absorbing layer, of a semiconductor containing at least one impurity of one conductivity type, an active layer, of a semiconductor providing lattice matching between itself and the light absorbing layer and having a larger band gap than that of the semiconductor of the light absorbing layer, the active layer being formed on the light absorbing layer and primarily containing at least one impurity of the said one conductivity type, and a surface layer, of a semiconductor providing lattice matching between itself and the active layer and having a larger band gap than that of the semiconductor of the light absorbing layer, the surface layer being formed on the active layer and primarily containing at least one impurity of the said one conductivity type, in a concentration less than that of the active layer, but the surface layer and an upper portion of the active layer having therein a region which contains at least one impurity of a conductivity type opposite to the said one conductivity type to provide a light sensitive region separated from other regions of the surface layer and the active layer by a well shaped p-n junction of which the bottom is located in the active layer.

Claim 9

An avalanche photodiode as claimed in any preceding claim, being a planar avalanche photodiode.

Claim 10

An avalanche photodiode as claimed in any preceding claim, sensitive,to light in the wavelength range 1.2 micrometers to 1.65 micrometers.

Claim 11

An avalanche photodiode as claimed in any preceding claim, wherein the light absorbing layer and the active layer are of respective group III-V compound or alloy semiconductors.

Claim 12

An avalanche photodiode as claimed in claim 7, wherein the light absorbing layer is of In x Ga 1-x As P 1- y and the active layer is of InP.

Claim 13

An avalanche photodiode as claimed in claim 7, wherein the light absorbing layer is of GaSb and the active layer is of Ga x Al 1-x Sb.

Claim 14

An avalance photodiode as claimed in any preceding claim, having layers continuously grown using liquid phase epitaxy.