Nitride HEMT Laminate Off-Angle for Thin-Channel Carrier Mobility
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Solution Overview
Problem
High electron mobility transistors (HEMTs) using group 13 nitride single crystal substrates face challenges in maintaining high carrier density and mobility due to the reduction caused by thinning of the channel layer, leading to issues with parasitic capacitance and leak current at high frequency operations.
Innovation Solution
A laminate structure comprising a group 13 nitride single crystal substrate with a buffer layer, a channel layer of 700 nm or smaller, and a barrier layer, where the first main face of the substrate has an off-angle of 0.4° to 1.0°, improving surface flatness and carrier mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the channel layer thickness is reduced to suppress parasitic capacitance and improve high-frequency performance, then the parasitic capacitance is reduced, but the sheet carrier density and carrier mobility are reduced
Solution Approach 1:
The invention changes the physical and chemical parameters of the substrate by introducing a specific off-angle (0.4° to 1.0°) to the first main face of the group 13 nitride single crystal substrate. This parameter change in substrate orientation improves surface flatness and suppresses reduction of sheet carrier density and carrier mobility, allowing thin channel layers to maintain high carrier characteristics while achieving low parasitic capacitance for high-frequency operation
Solution Approach 2:
The invention uses a composite structure consisting of a group 13 nitride single crystal substrate with specific off-angle, a buffer layer, a thin channel layer (700 nm or smaller), and a barrier layer. This composite laminate structure combines the advantages of each layer to achieve both low parasitic capacitance and high carrier mobility, resolving the contradiction between thin channel thickness and carrier density maintenance
2Reliability
If homo epitaxial growth is used to reduce defects from lattice mismatch, then defect generation is reduced, but manufacturing complexity increases
Solution Approach 1:
The invention uses homo epitaxial growth by selecting a group 13 nitride single crystal substrate with the same material composition as the channel layer. This eliminates lattice mismatch and thermal expansion coefficient differences, significantly reducing defect generation. The specific off-angle parameter (0.4° to 1.0°) further optimizes surface flatness and growth conditions, making the homo epitaxial process more controllable and less complex
Data Source
AI summary
A laminate includes a group 13 nitride single crystal substrate composed of a group 13 nitride single crystal and having a first main face and a second main face, a buffer layer provided on the first main face of the group 13 nitride single crystal substrate, a channel layer provided on the buffer layer and a barrier layer provided on the channel layer. The channel layer has a thickness of 700 nm or smaller, and the first main face of the group 13 nitride single crystal substrate has an off-angle of 0.4° or more and 1.0° or less.