Digital Alloy Back Barrier for GaN Transistors
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Solution Overview
Problem
The challenge in increasing channel conductivity of GaN transistors is limited by lattice mismatch issues when using high Aluminum content AlGaN as a back barrier, leading to strain and cracking problems.
Innovation Solution
A digital alloy back barrier with a superlattice structure, comprising alternating layers of Aluminum Nitride and Gallium Nitride, is used to improve channel conductivity while mitigating strain, replacing traditional analog AlGaN alloys.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high Aluminum content AlGaN is used as back barrier to increase channel conductivity, then channel conductivity is improved, but lattice mismatch strain and cracking occur
Solution Approach 1:
The continuous AlGaN back barrier layer is segmented into multiple thin alternating layers of AlN and GaN forming a superlattice structure. Each layer has thickness less than 10 nanometers, creating a digital alloy that maintains high aluminum content for conductivity while reducing lattice mismatch strain through the periodic structure.
Solution Approach 2:
The patent uses a composite digital alloy structure combining AlN and GaN layers in a superlattice configuration. This composite material approach allows achieving high effective aluminum content for improved channel conductivity while the alternating low-strain GaN layers prevent cracking and maintain lattice stability.
2Reliability
If thick analog AlGaN with high Al content is used as back barrier, then channel conductivity increases, but the material cannot be grown on GaN buffer due to lattice mismatch
Solution Approach 1:
The thick continuous AlGaN layer is divided into thin alternating AlN and GaN layers with each layer less than 10 nanometers thick. This segmentation enables the structure to be grown on GaN buffer without lattice mismatch issues while maintaining the effective high aluminum content needed for conductivity.
Solution Approach 2:
The patent changes the structural parameters from a continuous thick layer to a periodic superlattice with layer thickness less than 10 nanometers. This parameter change transforms the growth feasibility while maintaining the electrical properties through the digital alloy effect.
Data Source
AI summary
A III-nitride power handling device and the process of making the III-nitride power handling device are disclosed that use digital alloys as back barrier layer to mitigate the strain due to lattice mismatch between the channel layer and the back barrier layer and to provide increased channel conductivity. An embodiment discloses a GaN transistor using a superlattice binary digital alloy as back barrier comprising alternative layers of AlN and GaN. Other embodiments include using superlattice structures with layers of GaN and AlGaN as well as structures using AlGaN/AlGaN stackups that have different Aluminum concentrations. The disclosed device has substantially increased channel conductivity compared to traditional analog alloy back barrier devices.