GaN Light-Emitting Structure With 4H-SiC for Uniform Current Injection
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Solution Overview
Problem
VCSELs using GaN-based semiconductor materials face high resistivity in p-type semiconductor layers, leading to inefficient current injection into the active layer, which affects light emission uniformity and efficiency.
Innovation Solution
A light-emitting device design incorporating a first multi-layer film mirror, a light-emitting layer, a GaN-based semiconductor layer, and a second semiconductor layer with a higher band gap than the light-emitting layer but lower than the GaN-based semiconductor layer, where the second semiconductor layer is composed of 4H-SiC, facilitating better current injection and uniform light generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a p-type GaN-based semiconductor layer is used, then the device can emit blue and green laser light, but the high resistivity of the p-type layer prevents efficient current injection into the active layer
Solution Approach 1:
A p-type AlGaN layer with lower resistivity than p-type GaN is introduced as an intermediate layer between the p-type GaN active layer and the electrode. This intermediary layer facilitates better current injection while maintaining the light-emitting properties of the GaN-based structure.
Solution Approach 2:
The patent applies different material compositions locally: the active layer region uses p-type GaN for optimal light emission, while the contact region uses p-type AlGaN with lower resistivity for optimal current injection. This local differentiation resolves the contradiction between emission intensity and current injection efficiency.
2Device complexity
If the electrode is positioned at the end portion of the p-type semiconductor layer, then the structure is simplified, but current injection into the center of the active layer becomes less efficient
Solution Approach 1:
The patent transitions from a one-dimensional current path (electrode at end portion) to a two-dimensional current distribution (electrode overlapping with active layer through the transparent conductive oxide layer). This dimensional change enables uniform current injection across the active layer area while maintaining structural simplicity.
Solution Approach 2:
The patent changes the electrical parameters of the structure by introducing a transparent conductive oxide layer with high transparency and appropriate conductivity. This parameter change allows the electrode to be positioned for both structural simplicity and current injection efficiency.
3Reliability
If a transparent conductive oxide layer is added between the electrode and the active layer, then current injection efficiency improves, but the device structure becomes more complex
Solution Approach 1:
The transparent conductive oxide layer performs multiple functions simultaneously: it serves as an electrode contact layer for current injection, maintains optical transparency for light extraction, and provides structural support. This multi-functionality justifies the additional layer by consolidating multiple requirements into a single component.
Solution Approach 2:
The patent uses composite material structures, combining the transparent conductive oxide layer with the p-type AlGaN contact layer to create a composite contact structure that optimizes both electrical and optical properties while managing the overall device complexity.
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 design enables efficient and uniform current injection into the light-emitting layer, reducing resistivity and absorption loss, and enhancing light emission uniformity and efficiency.
Implementation Method 1
a light-emitting layer 30 provided between the first multi layer film mirror 20 and the second multi layer film mirror 70
Implementation Method 2
a first multi layer film mirror 20 composed of a plurality of first semiconductor layers 22 each having first conductivity type... a GaN-based semiconductor layer 40 having second conductivity type different from the first conductivity type
Implementation Method 3
A band gap of a material of the semiconductor layer of the second conductivity type is greater than a band gap of a material of the light-emitting layer, and smaller than a band gap of a material of the GaN-based semiconductor layer
Data Source
AI summary
A light-emitting device includes a first multi layer film mirror composed of a plurality of first semiconductor layers having first conductivity type, a second multi layer film mirror, a light-emitting layer provided between the first multi layer film mirror and the second multi layer film mirror, a GaN-based semiconductor layer having second conductivity type different from the first conductivity type, the GaN-based semiconductor layer being provided between the light-emitting layer and the second multi layer film mirror, a second semiconductor layer having the second conductivity type, the second semiconductor layer including a first portion provided between the GaN-based semiconductor layer and the second multi layer film mirror, and a second portion not overlapping the second multi layer film mirror as viewed in a lamination direction of the first multi layer film mirror and the light-emitting layer, and an electrode provided at the second portion. A band gap of a material of the second semiconductor layer is greater than a band gap of a material of the light-emitting layer, and smaller than a band gap of a material of the GaN-based semiconductor layer.