Formation of Ohmic contacts in III-nitride light emitting devices

• US 7,345,323 B2
• Filed: 03/30/2005
• Issued: 03/18/2008
• Est. Priority Date: 06/05/1998
• Status: Expired due to Term

• Current Assignee: Lumileds LLC (Apollo Global Management, Inc.)
• Original Assignee: Philips Lumileds Lighting Company LLC (Apollo Global Management, Inc.)
• Inventors: Kern, R. Scott, Christenson, Gina L., Kuo, Chihping, Martin, Paul Scott, Goetz, Werner K., Camras, Michael D., Steigerwald, Daniel A.
• Primary Examiner(s): Pert; Evan
• Assistant Examiner(s): Tran; Tan N.
• Application Number:
  US11/095,854
• Publication Number:
  US 20050167693A1
• Time in Patent Office: 1,084 Days
• Field of Search: 257/94,96,97,103
• US Class Current: 257/101
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: H01L 33/32 containing nitrogen
• CPC Class Codes: H01L 33/40 Materials therefor
• CPC Class Codes: H01S 5/0421 characterised by the semiconducting contacting layers electrodes H01S5/0425
• CPC Class Codes: H01S 5/04257 having positive and negative electrodes on the same side of the substrate
• CPC Class Codes: H01S 5/32341 blue laser based on GaN or GaP

Abstract

P-type layers of a GaN based light-emitting device are optimized for formation of Ohmic contact with metal. In a first embodiment, a p-type GaN transition layer with a resistivity greater than or equal to about 7 Ω cm is formed between a p-type conductivity layer and a metal contact. In a second embodiment, the p-type transition layer is any III-V semiconductor. In a third embodiment, the p-type transition layer is a superlattice. In a fourth embodiment, a single p-type layer of varying composition and varying concentration of dopant is formed.

Claims

1. A light-emitting diode comprising:

a substrate;

an n-type layer of GaN formed over the substrate;

an active region, formed over the n-type layer;

a p-type Al_xGa<sub>(1−

x)</sub>N (0≦

×

≦

1) layer, formed over the active region;

a p-type transition layer, formed over the p-type Al_xGa<sub>(1−

x)</sub>N layer, the p-type transition layer comprising a superlattice, the superlattice further comprising;

a first sublayer of doped p-type material;

a second sublayer of material, wherein a concentration of dopant in the second sublayer is less than a concentration of dopant in the first sublayer; and

a metal n-type contact and a metal p-type contact, the n-type contact being connected to the n-type layer, the p-type contact being directly connected to the p-type transition layer superlattice.

2. The light-emitting diode of claim 1 wherein the dopant is Mg and the dopant concentration of the first sublayer is about 1e20 cm⁻

3 to about 5e21 cm<sup>−

3</sup>.

3. The light-emitting diode of claim 1 wherein the dopant is Mg and the dopant concentration of the second sublayer is undoped to about 1e20 cm⁻

3.

4. The light-emitting diode of claim 1 wherein each of the first and second sublayers has a thickness from about 2 to about 20 nm.

5. The light emitting diode of claim 1 wherein a driving voltage of the light emitting diode is less than about 3.5 volts.

6. The light-emitting diode of claim 1 wherein the p-type contact is directly connected to the p-type transition layer.

7. A light emitting diode comprising:

a substrate;

an n-type layer of GaN formed over the substrate;

an active region, formed over the n-type layer;

a p-type Al_xGa<sub>(1−

x)</sub>N (0≦

×

≦

1) layer, formed over the active region;

a p-type transition layer, formed over the p-type Al_xGa<sub>(1−

x)</sub>N layer, the p-type transition layer comprising a sublayer of a p-type doped material and a sublayer consisting essentially of a single element; and

an n-type contact and a p-type contact, the n-type contact being connected to the n-type layer, the p-type contact being connected to the p-type transition layer.

8. The light emitting diode of claim 7 wherein the element is Mg.

9. The light emitting diode of claim 7 further comprising a p-type conductive layer of GaN, formed over the p-type Al_xGa₍₁₋

x)N layer.

10. The light emitting diode of claim 7 wherein a driving voltage of the light emitting diode is less than about 3.5 volts.

11. The light-emitting diode of claim 7 wherein the p-type contact is directly connected to the p-type transition layer.