Nitride Semiconductor Light-Emitting Device Cap Layer Structure
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Solution Overview
Problem
Nitride semiconductor light emitting devices face issues with quality degradation due to excessive Mg diffusion into the active layer and thermal deterioration, leading to decreased light-emission efficiency and insufficient light output.
Innovation Solution
A nitride semiconductor light emitting device is designed with a two-layered cap structure comprising a thick undoped GaN cap layer and a thin undoped AlGaN cap layer with a low Al composition ratio, which inhibits Mg diffusion and thermal deterioration, maintaining the quality of the multi-quantum well active layer and enhancing light emission efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a p-type AlGaN layer with high Al composition ratio (0.1 or greater) is formed to create barrier potential, then the electron barrier function is improved, but Mg diffusion into the active layer increases causing quality deterioration
Solution Approach 1:
The patent divides the single p-type AlGaN layer into multiple layers with different Al composition ratios. The first p-type AlGaN layer has a lower Al composition ratio (0.05-0.15) to minimize Mg diffusion, while the second p-type AlGaN layer has a higher Al composition ratio (0.15-0.3) to provide sufficient barrier potential. This segmentation allows each layer to perform its specific function optimally without compromising the other.
Solution Approach 2:
Different regions of the p-type AlGaN structure are assigned different Al composition ratios tailored to their specific functions. The first layer near the active layer uses lower Al content for Mg diffusion prevention, while the second layer uses higher Al content for barrier potential creation. This local quality variation resolves the contradiction by optimizing each region for its primary purpose.
2Manufacturing precision
If the substrate temperature is raised during intermediate layer growth to improve layer formation, then the layer quality is improved, but thermal deterioration of the active layer occurs
Solution Approach 1:
The patent forms the cap layers (undoped GaN layer and undoped AlGaN layer) before forming the p-type AlGaN layers. These cap layers are grown at lower temperatures to protect the active layer from thermal damage. Subsequently, the substrate temperature is raised for forming the p-type AlGaN layers, achieving good layer formation quality without thermally deteriorating the active layer due to the protective cap layers already in place.
Solution Approach 2:
The undoped GaN layer and undoped AlGaN layer serve as intermediary protective layers between the active layer and the high-temperature processing environment. These cap layers are grown first and remain in place during subsequent high-temperature growth of p-type layers, mediating the thermal stress and preventing direct thermal damage to the active layer while still allowing quality layer formation.
3Reliability
If a large amount of Mg is doped in the first p-type AlGaN layer to decrease bulk resistance, then the electrical conductivity is improved, but excessive Mg diffusion into the active layer occurs
Solution Approach 1:
The patent segments the Mg doping function across two layers. The first p-type AlGaN layer has lower Al content and moderate Mg doping to provide initial conduction with minimal diffusion. The second p-type AlGaN layer has higher Al content and higher Mg doping to provide the majority of the barrier potential while the lower-Al first layer acts as a diffusion barrier. This segmentation allows bulk resistance to be managed without excessive Mg diffusion.
Solution Approach 2:
Different Mg doping concentrations are applied locally in different layers. The first layer has lower Mg concentration optimized for low diffusion, while the second layer has higher Mg concentration optimized for barrier potential and conductivity. This local optimization of doping concentration resolves the contradiction between achieving low bulk resistance and preventing Mg diffusion.
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 optimized cap layer structure effectively prevents Mg diffusion and thermal degradation, resulting in improved light emission efficiency and sufficient light output, with higher efficiency maintained across a range of electric currents.
Implementation Method 1
a first cap layer comprising an undoped GaN layer and a thin undoped AlGaN layer, in this order from the active layer side, and a p-type AlGaN electron barrier layer which is doped with Mg and has a higher Al composition ratio than the AlGaN cap layer
Implementation Method 2
the first cap layer is formed at a lower temperature than a temperature at which a second cap layer is to be formed. Accordingly, it is possible to prevent rise in temperature of the substrate, and to prevent thermal deterioration of the active layer
Implementation Method 3
a p-type AlGaN electron barrier layer which is doped with Mg and has a higher Al composition ratio than the AlGaN cap layer and serves as an electron barrier layer to trap electrons in the active layer
Implementation Method 4
the first p-type AlGaN layer is doped with a large amount of Mg for decreasing the bulk resistance
Data Source
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AI summary
A nitride semiconductor light emitting device which offers sufficient light output, and a manufacturing method for the nitride semiconductor light emitting device are provided, the nitride semiconductor light emitting device has a first clad layer 13 including an n-type nitride semiconductor, an active layer 14 formed on the first clad layer 13, and including an In-containing nitride semiconductor, a GaN layer 17 formed on the active layer 14, a first AlGaN layer 18 formed on the GaN layer 17, and having a first Al composition ratio, a p-type second AlGaN layer 19 formed on the first AlGaN layer 18, having a second Al composition ratio higher than the first Al composition ratio, and containing a larger amount of Mg than the GaN layer 17 and the first AlGaN layer 18, and a second clad layer 20 formed on the second AlGaN layer 19, and including a p-type nitride semiconductor.