Gallium-nitride based multi-quantum well light-emitting diode n-type contact layer structure

Abstract

A structure for the n-type contact layer in the GaN-based MQW LEDs is provided. Instead of using Si-doped GaN as commonly found in conventional GaN-based MQW LEDs, the n-type contact layer provided by the present invention achieves high doping density (>1×1019 cm−3) and low resistivity through a superlattice structure combining two types of materials, AlmInnGa1-m-nN and AlpInqGa1-p-qN (0≦m, n<1, 0<p, q<1, p+q≦1, m<p), each having its specific composition and doping density. In addition, by controlling the composition of Al, In, and Ga in the two materials, the n-type contact layer would have a compatible lattice constant with the substrate and the epitaxial structure of the GaN-based MQW LEDs. This n-type contact layer, therefore, would not chap from the heavy Si doping, have a superior quality, and reduce the difficulties of forming n-type ohmic contact electrode. In turn, the GaN-based MQW LEDs would require a lower operation voltage.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention generally relates to the gallium-nitride based multi-quantum well light-emitting diodes and, more particularly, to the n-type contact layer structure of the gallium-nitride based multi-quantum well light-emitting diodes. [0003] 2. The Prior Arts [0004] Gallium-nitride (GaN) materials can achieve a wide range of band gaps by controlling the GaN-based materials' compositions. As such, various colored light-emitting diodes (LEDs), especially those blue or purple light LEDs that require wide band gaps, can be produced using GaN-based materials. These GaN-based LEDs therefore have been the research and development focus in recent years. [0005] Within conventional GaN-based LEDs, the active layers usually adopt a multi-quantum well (MQW) structure with GaN and indium-gallium-nitride (InxGa1-xN, 0≦x≦1) as potential wells. Photons are then generated through the recombination of the electrons and holes ...

AI Technical Summary

Benefits of technology

The present invention provides an improved epitaxial structure for the n-type GaN contact layers of GaN-based MQW LEDs. This structure overcomes the limitations and disadvantages of previous methods. The theory behind the invention involves combining two types of material, each with specific composition and doping density, to achieve a compatible lattice constant with the substrate and the epitaxial structure of the LEDs. This results in a superior quality n-type contact layer that is not affected by heavy Si doping, and reduces the difficulty of forming an n-type ohmic contact electrode. Ultimately, the LEDs require a lower operation voltage.

Problems solved by technology

However, it is observed that, during practical fabricating processes, the n-type GaN contact layer would be easily chapped and snapped, as the heavy Si doping causes incompatible lattice constants among the epitaxial layers of the GaN-based MQW LEDs, that, in turn, causes excessive stress to develop and accumulate.

These undesirable results not only affect the epitaxial quality of the GaN-based MQW LEDs, but also add additional difficulties in the formation of the n-type ohmic contact electrode on top of the n-type GaN contact layer.

In summary, these shortcomings would result in an inferior electrical characteristics or conductivity in the GaN-based MQW LEDs.

In the worst case, the GaN-based MQW LEDs would be un-useable.

Therefore, the GaN-based MQW LEDs containing this type of conventional n-type GaN contact layers, on one hand, require a higher operation voltage and, thereby, consume more powers.

On the other hand, the GaN-based MQW LEDs would have a low yield rate, causing the production cost to rise.

Additionally, pin holes are easier to form in the heavily Si-doped n-type GaN contact layer, causing the semiconducting characteristics of the GaN-based MQW LEDs to deteriorate.

Current leakage is also possible during the operation of the GaN-based MQW LEDs.

Images