Nitride Semiconductor Reflector With Composition-Graded Layers
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Solution Overview
Problem
Nitride semiconductor multilayer film reflectors face high resistance due to the wide-gap nature of nitride semiconductor materials and significant polarization effects at heterojunction interfaces, hindering current injection.
Innovation Solution
A nitride semiconductor multilayer film reflector is designed with a first semiconductor layer, a second semiconductor layer, and composition-graded layers interposed between them, where the composition-graded layers have a decreasing Al composition approaching the second semiconductor layer, and are doped with n-type impurities at concentrations above 5×10^19 cm^-3 to reduce energy barriers and polarization effects, ensuring continuous energy levels and enhanced carrier mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If nitride semiconductor layers with large bandgap energy difference are used to achieve high reflectance, then reflectance is improved, but hetero barrier increases causing high resistance
Solution Approach 1:
A composition-graded layer is introduced as an intermediary between the first and second nitride semiconductor layers. This graded layer has Al composition that gradually changes from the first layer to the second layer, serving as a transition region that reduces the hetero barrier while maintaining the high reflectance properties of the original layer structure.
Solution Approach 2:
The composition-graded layer is doped with n-type impurities at a concentration of not less than 5×10^19 cm^-3, creating a highly conductive region locally at the heterojunction interface. This localized high doping concentration reduces the energy barrier specifically at the interface without affecting the overall bandgap structure needed for high reflectance.
2Illumination intensity
If nitride semiconductor material is used for multilayer film reflector, then high reflectance is achieved, but polarization effect produces energy barrier causing high resistance
Solution Approach 1:
The Al composition in the composition-graded layer is continuously changed from the first nitride semiconductor layer to the second nitride semiconductor layer. This gradual parameter change in composition reduces the polarization effect and associated energy barrier at the heterojunction interface, while maintaining the optical properties needed for high reflectance.
Solution Approach 2:
High concentration n-type doping (≥5×10^19 cm^-3) is applied specifically to the composition-graded layer at the heterojunction interface, creating a localized region with enhanced carrier concentration that compensates for the polarization-induced energy barrier without affecting the bulk material properties.
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 reduces the energy barrier and resistance of the nitride semiconductor multilayer film reflector, enabling effective current injection and improving the performance of nitride semiconductor light-emitting devices by reducing internal loss and threshold current, while maintaining high reflectance and crystallinity.
Implementation Method 1
Energy levels of electrons at bottoms of conduction bands of the first and second semiconductor layers and the first and second composition-graded layers are continuous without band offset
Implementation Method 2
an extremely large polarization was formed on the junction interface between the first and second semiconductor layers having different reflectances by a polarization effect peculiar to the nitride semiconductor material
Implementation Method 3
The first composition-graded layer has an n-type impurity concentration of not less than 5×10^19 cm−3
Implementation Method 4
the first and second semiconductor layers having a large refractive index difference, namely, a large bandgap energy difference therebetween are selected in order to realize a high reflectance
Data Source
AI summary
Achieving resistance reduction of a nitride semiconductor multilayer film reflector. In the nitride semiconductor multilayer film reflector, a first semiconductor layer has a higher Al composition than a second semiconductor layer. A first composition-graded layer is interposed between the first and second semiconductor layers so as to be located at a group III element face side of the first semiconductor layer, the first composition-graded layer being adjusted so that its Al composition becomes lower as coming close to the second semiconductor layer. A second composition-graded layer is interposed between the first and second semiconductor layers so as to be located at a nitride face side of the first semiconductor layer. The second composition-graded layer is adjusted so that its Al composition becomes lower as coming close to the second semiconductor layer.