GaN HEMT Initial Layer Mitigates Lattice Mismatch
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Solution Overview
Problem
Compound semiconductor devices, such as GaN-based HEMTs, face challenges in forming layers of appropriate thickness due to lattice constant differences, leading to distortion and cracks, despite the use of buffer layers, which reduces desirable characteristics and electron mobility.
Innovation Solution
Incorporating an initial layer of Group III atoms with higher ductility than the core Group III-V compound semiconductor layer to mitigate lattice constant differences and reduce the likelihood of cracks, while also minimizing pit formation and ensuring layer flatness, thereby enhancing electron mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If compound semiconductor layers are formed by MOVPE method, then the layers can be manufactured with controlled composition, but lattice constant differences cause distortion and cracks as layers become thicker
Solution Approach 1:
The compound semiconductor layer is segmented into multiple sub-layers with different Al contents. The first sub-layer has lower Al content (0.2-0.3) and the second sub-layer has higher Al content (0.3-0.4), allowing gradual transition of lattice constants to reduce distortion and prevent cracks while maintaining manufacturing precision
Solution Approach 2:
Different regions of the semiconductor layer have different Al contents tailored to local requirements. The first sub-layer near the AlN layer has lower Al content to match lattice constants and reduce distortion, while the second sub-layer has higher Al content to achieve desired electrical characteristics
2Stability of the object's composition
If buffer layer is added to reduce distortion, then lattice mismatch is mitigated, but cracks are still found in compound semiconductor layer
Solution Approach 1:
The semiconductor layer is divided into first and second sub-layers with progressively increasing Al content. This segmentation allows gradual accommodation of lattice mismatch rather than abrupt transition, reducing stress concentration that causes cracks even when buffer layers are present
Solution Approach 2:
The Al content parameter is changed gradually from 0.2-0.3 in the first sub-layer to 0.3-0.4 in the second sub-layer. This parameter transition smoothly changes lattice constants to match the buffer layer while building up the desired layer thickness without crack formation
3Reliability
If compound semiconductor layer thickness is increased to provide desirable characteristics, then device performance improves, but distortion increases and cracks are likely to form
Solution Approach 1:
The thick semiconductor layer is segmented into multiple sub-layers that can be formed sequentially. Each sub-layer is thin enough to avoid crack formation during formation, but the cumulative thickness provides the desirable electrical characteristics needed for device performance
Solution Approach 2:
Different thicknesses and Al contents are applied to different sub-layers based on local requirements. The first sub-layer provides lattice matching with thinner effective thickness, while the second sub-layer adds thickness for electrical performance with optimized Al content
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 use of initial layers with higher ductility reduces distortion and crack formation, resulting in more stable and higher electron mobility in compound semiconductor devices, improving their performance and reliability.
Implementation Method 1
lattice constants are different between compound semiconductor layers of different materials and also between a compound semiconductor layer and a substrate, so that distortion increases as the compound semiconductor layer becomes thicker
Implementation Method 2
with the heterostructure of the GaN layer and the AlGaN layer, piezoelectric polarization is induced in the AlGaN layer due to the lattice distortion of both layers, generating two-dimensional electron gas (2DEG) of high concentration at an interface between the GaN layer and the AlGaN
Data Source
AI summary
A compound semiconductor device includes a substrate; an initial layer formed over the substrate; and a core layer which is formed over the initial layer and contains a Group III-V compound semiconductor. The initial layer is a layer of Group III atoms of the Group III-V compound semiconductor contained in the core layer.