Polar AlGaN p-Type Layer Structure for High Hole Injection
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Solution Overview
Problem
The challenge is to achieve a low resistance p-type semiconductor layer with a high hole concentration for nitride semiconductor light emitting devices, particularly in the AlGaN system, as deep acceptor levels in p-type nitride semiconductors hinder efficient hole injection and light emission.
Innovation Solution
A semiconductor apparatus is designed with a p-type semiconductor layer composed of multiple unit semiconductor layers, each with a p-type nitride semiconductor having a polar or semi-polar surface. The composition of each unit semiconductor layer changes in the stacking direction, increasing the lattice constant in the c-axis positive direction, which enhances hole concentration through increased negative polarization charges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a p-type layer including AlGaN with an inclined Al composition is used to achieve high hole concentration, then the hole concentration can be increased, but the hole concentration decreases as the layer thickness of the p-type layer increases
Solution Approach 1:
The p-type layer is divided into multiple sub-layers with different Al compositions (first p-type layer with higher Al composition, second p-type layer with lower Al composition). This segmentation allows each sub-layer to contribute differently to hole concentration while maintaining overall high hole concentration throughout the structure, resolving the trade-off between layer thickness and hole concentration.
Solution Approach 2:
Different regions of the p-type layer are assigned different Al compositions optimized for their specific functions: the first p-type layer with higher Al composition provides high hole concentration, while the second p-type layer with lower Al composition facilitates hole injection. This local optimization allows the entire structure to achieve high hole concentration without requiring excessive total thickness.
2Quantity of substance
If a superlattice structure doped with acceptor impurities is used to achieve high hole concentration, then high hole concentration can be obtained through polarization field, but the AlGaN barrier layer inhibits hole injection from the p-type layer to the active layer
Solution Approach 1:
The p-type layer is structured with spatially varying Al composition: the first p-type layer has higher Al content optimized for generating high hole concentration via polarization effects, while the second p-type layer has lower Al content optimized for reducing barrier height and facilitating hole injection into the active layer. This local differentiation resolves the contradiction between achieving high hole concentration and enabling efficient hole injection.
Solution Approach 2:
The p-type layer is constructed as a composite structure combining two AlGaN layers with different compositions. This composite approach allows simultaneous exploitation of the high polarization field in Al-rich regions for hole generation and the lower barrier properties in Ga-rich regions for hole injection, resolving the harmful effect of uniform Al composition.
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 results in a p-type semiconductor layer with a high hole concentration, improving hole injection efficiency and light emission intensity, particularly in deep ultraviolet light emitting devices.
Implementation Method 1
each of the plurality of unit semiconductor layers has a composition changing in a stacking direction... increasing the lattice constant in the c-axis positive direction, which enhances hole concentration through increased negative polarization charges
Data Source
AI summary
A p-type semiconductor layer includes a plurality of unit semiconductor layers, and each of the plurality of unit semiconductor layers includes a p-type nitride semiconductor whose main surface is a polar surface or a semi-polar surface. The nitride semiconductor constituting the unit semiconductor layer includes nitrogen and two or more elements, and each of the plurality of unit semiconductor layers has a composition changing in a stacking direction such that, for example, a lattice constant in a c-axis direction increases in a c-axis positive direction.