Nitride Semiconductor Light-Emitting Device Composition-Graded Layers
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Solution Overview
Problem
Nitride semiconductor light-emitting devices face challenges in achieving high positive hole injection efficiency due to low positive hole mobility and unintended polarization fixed charges in multilayer structures, which can block current injection and complicate device design.
Innovation Solution
A nitride semiconductor light-emitting device is designed with a stacked structure of nitride semiconductor crystals in the +c-axis direction, featuring an active layer interposed between composition-graded layers that reduce Al composition values as they approach the interface with negative polarization, averaging negative polarization fixed charges and forming p-type regions to enhance positive hole injection efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a multilayer structure is adopted to improve light emission efficiency, then light emission efficiency is improved, but unintended polarization fixed charge occurs at interfaces which blocks current injection
Solution Approach 1:
The patent applies local quality by creating composition-graded layers with varying Al composition values at different positions. The first composition-graded layer has a specific Al composition range (0.05-0.2) at its first interface with the active layer, while the second composition-graded layer has a different Al composition range (0.15-0.3) at its third interface with the active layer. This local variation in composition allows control over polarization fixed charge distribution at specific interfaces, enabling current injection improvement without sacrificing light emission efficiency from the multilayer structure.
2Reliability
If Al composition is increased in composition-graded layers to reduce polarization field influence, then carrier injection efficiency is improved, but positive hole concentration decreases
Solution Approach 1:
The patent applies parameter changes by precisely controlling the Al composition values in the composition-graded layers. The first composition-graded layer maintains Al composition between 0.05-0.2 at its first interface with the active layer, while the second composition-graded layer maintains Al composition between 0.15-0.3 at its third interface with the active layer. This parameter optimization balances two competing requirements: reducing polarization field influence (which requires higher Al composition) and maintaining positive hole concentration (which requires lower Al composition), thereby achieving both improved carrier injection efficiency and adequate positive hole concentration.
3Reliability
If composition-graded layers are added to control polarization fixed charge, then current injection is improved, but device structure becomes more complex
Solution Approach 1:
The patent applies segmentation by dividing the structure into distinct functional layers: an active layer, a first composition-graded layer, and a second composition-graded layer. Each layer serves a specific function - the active layer for light emission, and the composition-graded layers for controlling polarization fixed charge and improving current injection. This segmentation allows systematic control of electrical properties without requiring complex overall device architecture, as each layer independently contributes to the desired performance.
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
This configuration increases positive hole concentrations in the composition-graded layers, improving positive hole injection and current injection efficiency into the active layer, while reducing unintentional polarization fixed charges and simplifying device design.
Implementation Method 1
polarization fixed charge which is generated on a crystal interface by spontaneous polarization or piezoelectric polarization each as a physical property inherent in a nitride semiconductor material
Implementation Method 2
polarization fixed charge which is generated on a crystal interface by spontaneous polarization or piezoelectric polarization each as a physical property inherent in a nitride semiconductor material
Implementation Method 3
each one of the first and second composition-graded layers is composition-graded so that an Al composition value thereof is rendered smaller as each one of the first and second composition-graded layers comes close to a side where a sum of spontaneous polarization and piezoelectric polarization is negative
Data Source
AI summary
An object is to improve a positive hole injection efficiency into an active layer in a nitride semiconductor light-emitting device. The nitride semiconductor light-emitting device is formed by stacking nitride semiconductor crystals each of which contains Al and has a polar or semipolar surface either serving as a growth face. The device includes an active layer (103), and first and second composition-graded layers (102, 104). The active layer (103) is interposed between the first and second composition-graded layers (102, 104). Each one of the first and second composition-graded layers is composition-graded so that an Al composition value is rendered smaller as each one of the first and second composition-graded layers (102, 104) comes close to a side where a sum of spontaneous polarization and piezoelectric polarization is negative.