SPSL P-side Layers for UV Nitride Emitters
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Solution Overview
Problem
Achieving high p-type conductivity and optical transparency in nitride-based light emitting devices, particularly in AlGaN p-side layers, is challenging due to the difficulty in doping these materials to achieve high hole concentrations and establishing a good electrical contact while maintaining sufficient conductivity and transparency at short wavelengths.
Innovation Solution
The use of a short period superlattice (SPSL) with alternating layers of AlxhighGa1-xhighN and AlxlowGa1-xlowN, where xlow≤xhigh≤0.9, in conjunction with a graded AlzGa1-zN p-contact layer, enhances hole concentration and conductivity by leveraging polarization enhanced doping and optimizing Al composition profiles to achieve low resistivity and high current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If p-type doping is increased to achieve high hole concentration, then conductivity is improved, but optical transparency deteriorates due to increased absorption losses
Solution Approach 1:
The p-side layer is segmented into a short period superlattice structure with alternating high-Al and low-Al composition layers. This segmentation allows the high-Al layers to provide transparency while the low-Al layers facilitate doping and conductivity, resolving the contradiction between transparency and conductivity.
Solution Approach 2:
Different regions of the p-side heterostructure have different Al compositions optimized for their specific functions: high-Al regions (x≥0.6) provide optical transparency, while lower-Al regions facilitate p-type doping and hole transport. This local quality differentiation resolves the contradiction between transparency and conductivity requirements.
2Object-generated harmful factors
If Al composition is increased to improve optical transparency, then absorption losses are reduced, but doping efficiency deteriorates making it difficult to achieve high hole concentrations
Solution Approach 1:
The superlattice structure segments the Al composition into alternating high and low regions, allowing high-Al layers to provide transparency while low-Al layers maintain doping efficiency. This segmentation resolves the contradiction between transparency and doping efficiency.
Solution Approach 2:
The Al composition parameter x is varied periodically within the superlattice, creating regions with different doping efficiencies. This parameter change allows the system to achieve both high transparency (in high-Al regions) and good doping efficiency (in low-Al regions) simultaneously.
3Reliability
If p-type dopant concentration is increased to improve hole concentration, then conductivity is improved, but the material becomes more difficult to dope maintaining sufficient transparency
Solution Approach 1:
The superlattice segments the doping function into specific low-Al layers while high-Al layers maintain transparency. This segmentation reduces doping difficulty by confining dopant incorporation to regions where it is most effective.
Solution Approach 2:
The low-Al composition layers act as intermediary regions that facilitate dopant incorporation and activation, mediating between the doping requirement and the transparency requirement of the high-Al layers.
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 approach significantly increases hole concentration and conductivity, enabling high current densities and low resistivity, while maintaining optical transparency and reducing absorption losses, thus improving the performance of ultraviolet light emitting diodes and laser diodes.
Implementation Method 1
The alternating layers cause modulation in a valence band potential in the SPSL and the modulation is approximately equal to an acceptor level energy of the p-type dopant
Data Source
AI summary
A light emitting device includes a p-side heterostructure having a short period superlattice (SPSL) formed of alternating layers of AlxhighGa1-xhighN doped with a p-type dopant and AlxlowGa1-xlowN doped with the p-type dopant, where xlow≤xhigh≤0.9. Each layer of the SPSL has a thickness of less than or equal to about six bi-layers of AlGaN.