Light-emitting semiconductor device and method of fabrication

• US 20050110029A1
• Filed: 11/22/2004
• Published: 05/26/2005
• Est. Priority Date: 11/26/2003
• Status: Active Grant

• Current Assignee: Sanken Electric Company Limited
• Original Assignee: Sanken Electric Company Limited
• Inventors: Sato, Masahiro, Otsuka, Koji, Aoyagi, Hidekazu
• Granted Patent: US 7,456,435 B2
• Time in Patent Office: Days
• US Class Current: 257/94
• CPC Class Codes: H01L 33/007 comprising nitride compounds
• CPC Class Codes: H01L 33/04 with a quantum effect structure or superlattice, e.g. tunnel junction
• CPC Class Codes: H01L 33/14 with a carrier transport control structure, e.g. highly-doped semiconductor layer or current-blocking structure

Abstract

A light-emitting diode having a silicon substrate on which there are successively formed a buffer layer, a p-type nitride semiconductor layer, an active layer, an n-type nitride semiconductor layer, and a current spreading layer. The current spreading layer is a lamination of a first and a second sublayer arranged alternately a required number of times. Composed of different compound semiconductors, the alternating sublayers of the current spreading layer create heterojunctions for offering the two-dimensional gas effect. The current spreading layer is so low in resistivity in a direction parallel to its major surface from which light is emitted, that the current is favorably spread therein for improved efficiency of light emission. A front electrode in the form of a metal pad is mounted centrally on the major surface of the current spreading layer in ohmic contact therewith.

Claims

1. A light-emitting semiconductor device of improved efficiency, comprising:

(a) a first compound semiconductor layer of a first conductivity type;

(b) an active layer of a compound semiconductor on the first compound semiconductor layer;

(c) a transparent second compound semiconductor layer of a second conductivity type, opposite to the first conductivity type, on the active layer;

(d) a transparent current spreading layer on the second compound semiconductor layer, the current spreading layer being a lamination of alternating first and second sublayers of different compound semiconductors;

(e) a first electrode electrically coupled to the current spreading layer so as to permit emission of light radiated from the active layer through the current spreading layer; and

(f) a second electrode electrically coupled to the first compound semiconductor layer.

2. A light-emitting semiconductor device as defined in claim 1, wherein the compound semiconductors of the alternating first and second sublayers of the current spreading layer are chosen to create two-dimensional carrier layers in the first sublayers due to heterojunctions between the first and the second sublayers.

3. A light-emitting semiconductor device as defined in claim 1, wherein at least either of the first and the second sublayers of the current spreading layer contains an impurity that determines the second conductivity type.

4. A light-emitting semiconductor device as defined in claim 1, wherein the second compound semiconductor layer has a bandgap greater than that of the active layer, and a thickness greater than each sublayer of the current spreading layer.

5. A light-emitting semiconductor device as defined in claim 1, wherein each first sublayer of the current spreading layer has a bandgap greater than that of the active layer and is fabricated from a nitride semiconductor of the second conductivity type containing aluminum in a first proportion that is equal to or greater than zero, and wherein each second sublayer of the current spreading layer has a bandgap greater than that of the active layer and is fabricated from a nitride semiconductor of the second conductivity type containing aluminum in a second proportion that is greater than the first proportion.

6. A light-emitting semiconductor device as defined in claim 1, wherein each first sublayer of the current spreading layer is less thick than the second compound semiconductor layer.

7. A light-emitting semiconductor device as defined in claim 1, wherein the first conductivity type is p-type, and the second conductivity type n-type.

8. A light-emitting semiconductor device as defined in claim 1, wherein the first electrode is formed in direct contact with the current spreading layer.

9. A light-emitting semiconductor device as defined in claim 1, further comprising an substrate of electrically conducting material on which there is formed the first compound semiconductor layer, the second electrode being formed on the substrate.

10. A method of making a light-emitting semiconductor device of improved efficiency, which comprises:

(a) providing a substrate;

(b) successively growing in a gaseous phase a first compound semiconductor layer of a first conductivity type and an active layer and a second compound semiconductor layer of a second conductivity type, in that order, on the substrate;

(c) growing in a gaseous phase a first current spreading sublayer of a first compound semiconductor on the second compound semiconductor layer;

(d) growing in a gaseous phase a second current spreading sublayer of a second compound semiconductor, different from the first compound semiconductor, on the first current spreading sublayer;

(e) repeating steps (c) and (d) a required number of times to provide as many alternations of the first and second current spreading sublayers constituting in combination a current spreading layer;

(f) creating a first electrode electrically coupled to the current spreading layer; and

(g) creating a second electrode electrically coupled to the first compound semiconductor layer.

11. A method of making a light-emitting semiconductor device of improved efficiency, which comprises:

(a) providing a growth substrate for growing semiconductors thereon;

(b) growing in a gaseous phase a first current spreading sublayer of a first compound semiconductor on the growth substrate;

(c) growing in a gaseous phase a second current spreading sublayer of a second compound semiconductor, different from the first compound semiconductor, on the first current spreading sublayer;

(d) repeating steps (b) and (c) a required number of times to provide as many alternations of the first and second current spreading sublayers constituting in combination a current spreading layer;

(e) successively growing in a gaseous phase a first compound semiconductor layer of a first conductivity type and an active layer and a second compound semiconductor layer of a second conductivity type, in that order, on the current spreading layer;

(f) creating a bond layer of electrically conducting material on at least either of the second compound semiconductor layer and a support substrate;

(g) joining the support substrate to the second compound semiconductor layer via the bond layer or layers;

(h) removing the growth substrate from the current spreading layer;

(i) creating a first electrode electrically coupled to the current spreading layer; and

(j) crating a second electrode electrically coupled to the second compound semiconductor layer.