Asymmetric P-Type Superlattice for UV LED Hole Injection
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Solution Overview
Problem
Achieving high p-type conductivity and reliability in group III nitride based optoelectronic devices, particularly UV LEDs, is challenging due to high acceptor activation energy and low hole mobility in Mg-doped AlGaN, leading to device lifetime degradation and inefficient carrier injection.
Innovation Solution
A heterostructure with an asymmetric p-type superlattice layer adjacent to a composition-graded electron blocking layer and a thin p-GaN contact layer, enhancing p-type conductivity and light collection through a reflective metal coating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heavy Mg doping is used to increase hole concentration, then p-type conductivity is improved, but acceptor activation energy increases and unintentional donor-like defects increase
Solution Approach 1:
The patent changes the doping approach by using polarization-induced carrier generation instead of heavy Mg doping. This is achieved by designing specific AlGaN layer compositions and thicknesses that exploit the piezoelectric effect to generate high hole concentrations without the harmful side effects of traditional doping
Solution Approach 2:
The patent replaces the chemical doping mechanism (Mg doping) with a physical mechanism (polarization-induced carrier generation). The piezoelectric field generated by lattice mismatch in the AlGaN heterostructure spontaneously generates carriers without requiring heavy impurity doping
2Productivity
If Al composition in electron blocking layer is increased to prevent electron overflow, then carrier injection efficiency is improved, but device complexity increases
Solution Approach 1:
The patent designs the AlGaN electron blocking layer to serve multiple functions simultaneously: it blocks electrons from the active region while also serving as a polarization-induced doping layer that generates holes. This multi-functionality reduces the need for additional separate layers, thereby reducing overall device complexity
3Ease of manufacture
If conventional thick p-GaN contact layer is used, then manufacturing is simplified, but p-type conductivity and light collection efficiency decrease
Solution Approach 1:
The patent dramatically reduces the thickness of the p-GaN contact layer from conventional thick layers to ultrathin dimensions (few nanometers). This parameter change is enabled by the polarization-induced carrier generation mechanism, which compensates for the reduced thickness and maintains high conductivity
Solution Approach 2:
The patent employs an ultrathin p-GaN film that would be too thin to provide adequate conductivity under conventional doping schemes. However, the polarization-induced carrier generation enables this thin film to achieve the required electrical properties, demonstrating the effectiveness of thin-film approach
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
Improves p-type conductivity and emitted light intensity, extending device lifetime and enhancing carrier injection efficiency in UV LEDs.
Implementation Method 1
polarization-assisted doping has been demonstrated as an alternative to the conventional thermally-activated hole generation
Implementation Method 2
a reflective (e.g., highly reflective) metal coating can be deposited on top of the thin p-GaN layer to boost the amount of light collected from the transparent substrate side
Data Source
AI summary
A heterostructure for an optoelectronic device is disclosed. The heterostructure includes an active region including at least one quantum well and at least one barrier and an electron blocking layer located adjacent to the active region, wherein the electron blocking layer includes a region of graded composition. An asymmetric p-type superlattice layer is located adjacent to the electron blocking layer, wherein the p-type superlattice includes at least one superlattice period comprising a set of wells and a set of barriers. A thickness of at least one of: each well in the set of wells or each barrier in the set of barriers varies along a length of the p-type superlattice.