Multilayered P-Type Contacts for DUV LEDs
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Solution Overview
Problem
Semiconductor deep-ultraviolet (DUV) light-emitting diodes (LEDs) face challenges such as degrading crystal quality, low conductivity, and poor carrier injection due to defects and absorption issues, particularly at sub-250 nm wavelengths, which affect internal quantum efficiency and light extraction.
Innovation Solution
A light-emitting device with a p-type contact comprising a hole injection layer, a p-type GaN layer, and a current tunneling layer made of an inorganic material with a wider bandgap, allowing efficient hole injection and carrier tunneling, and an active region with a multiple quantum well structure of group III-V nitride layers to enhance light emission efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a p-GaN contact layer is used to form a highly conductive ohmic contact, then electrical conductivity is improved, but light extraction is compromised due to absorption by the p-GaN contact layer at DUV wavelengths
Solution Approach 1:
The contact structure is divided into multiple functional layers: a highly doped p-GaN layer for electrical conduction, a thin AlGaN layer with lower aluminum content for reduced absorption, and a tunnel barrier layer for carrier injection. This segmentation allows each layer to optimize its specific function without compromising overall performance.
Solution Approach 2:
Different regions of the contact structure have different material compositions optimized for their local functions. The p-GaN layer has high doping for conductivity, while the AlGaN layer has lower aluminum content (x<0.5) to reduce absorption at DUV wavelengths, demonstrating local quality optimization.
2Use of energy by moving object
If high-Al-content AlGaN materials are used to achieve sub-250 nm wavelength emission, then light emission energy is improved, but crystal quality degrades due to defects related to non-radiative recombination
Solution Approach 1:
The aluminum content parameter is carefully controlled to be less than 0.5 in the AlGaN contact layer, balancing the need for high-energy DUV emission with the need to maintain acceptable crystal quality and minimize non-radiative recombination defects.
Solution Approach 2:
A thin tunnel barrier layer is introduced as an intermediary between the high-Al-content AlGaN active region and the p-GaN contact layer. This tunnel barrier facilitates carrier injection while protecting the crystal quality of the high-Al-content materials.
3Reliability
If p-type doping is increased to improve conductivity in AlGaN, then electrical conductivity is improved, but carrier injection remains poor due to large ionization energy of acceptors
Solution Approach 1:
A thin tunnel barrier layer is introduced as an intermediary between the p-GaN contact layer and the AlGaN active region. This tunnel barrier enables efficient carrier injection by providing a quantum tunneling path that overcomes the large ionization energy of acceptors in highly doped AlGaN.
Solution Approach 2:
The doping concentration parameter is optimized in the p-GaN layer to achieve high conductivity, while the tunnel barrier layer thickness is controlled to enable efficient carrier injection despite the large acceptor ionization energy in the AlGaN region.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution improves hole injection and light emission efficiency, reducing efficiency droop and increasing radiative recombination rates, leading to enhanced external quantum efficiency and wall-plug efficiency in DUV LEDs.
Implementation Method 1
a current tunneling layer disposed between the hole injection layer and the p-type layer. The current tunneling layer includes an inorganic material having a bandgap that is wider than the bandgaps of the p-type doped hole injecting semiconductor material and the p-type doped GaN
Implementation Method 2
Monolayer gallium nitride (GaN) quantum wells and dots between AlN barriers have been demonstrated to improve IQE, as carriers are kept away from non-radioactive recombination centers due to three-dimensional confinement
Implementation Method 3
researchers have developed polarization doping, the purpose of which is to enhance electrical conductivity and hole injection. Doping by varying the Al composition and the corresponding polarization strength has been employed to take advantage of the intrinsic spontaneous polarization effect to increase carrier concentration
Data Source
AI summary
Light-emitting devices having a multiple quantum well (MQW) pin diode structure are provided. The light-emitting devices include a multilayered p-type contact composed of a heavily p-type doped hole injection layer and a thin p-type group III-nitride layer. The materials of the hole injection layer and the p-type group III-nitride layer are separated by a layer of a material that allows current tunneling through the heterogeneous junction formed between the lattice mismatched materials.