GaN Barrier Layer Segmentation for Normally-Off Gate Control
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Solution Overview
Problem
Current GaN-based power devices, such as lateral HEMTs, are typically normally-on devices due to the high density of 2-DEG, making it challenging to manufacture normally-off devices with adequate conductivity in the drift region, and existing recessed-gate structures are complex and not reproducible.
Innovation Solution
A nitride semiconductor device with a Group-III nitride channel layer and a barrier layer having a first portion with reduced thickness under the gate, combined with a p-doped gate layer section, which reduces the 2-DEG density under the gate, allowing for a normally-off device with controlled threshold voltage and conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a p-doped AlGaN or p-doped GaN barrier layer is used to raise the conductivity band and shift the threshold voltage to positive values, then the device can achieve normally-off operation, but the undoped barrier layer produces a high density of 2-DEG that counteracts the threshold voltage rise
Solution Approach 1:
The barrier layer is divided into two distinct portions: a first portion with reduced thickness (5-15 nm) located directly under the gate, and a second portion with greater thickness (15-30 nm) in the drift region. This segmentation allows the first portion to reduce 2-DEG density under the gate for threshold voltage control, while the second portion maintains sufficient 2-DEG density for conductivity in the drift region.
Solution Approach 2:
Different thicknesses of the barrier layer are applied to different spatial locations: a thinner first portion under the gate to reduce 2-DEG density and improve threshold voltage control, and a thicker second portion in the drift region to maintain high conductivity. This local quality variation resolves the contradiction between threshold voltage control and drift region conductivity.
2Reliability
If the density of the 2-DEG is reduced to achieve normally-off operation, then the threshold voltage can be controlled, but the conductivity of the drift region between source and drain is reduced
Solution Approach 1:
The barrier layer is segmented into a first portion under the gate with thickness of 5-15 nm and a second portion in the drift region with thickness of 15-30 nm. This segmentation enables the first portion to reduce 2-DEG density for threshold voltage control while the second portion maintains sufficient 2-DEG density for drift region conductivity.
Solution Approach 2:
The barrier layer exhibits local quality variation with different thicknesses in different regions: thinner under the gate to reduce 2-DEG density and control threshold voltage, and thicker in the drift region to maintain high conductivity. This resolves the contradiction between threshold voltage control and drift region conductivity.
3Reliability
If a recessed-gate structure with reduced barrier thickness below the gate is formed, then the threshold voltage can be controlled, but the manufacturing process becomes complicated and less reproducible
Solution Approach 1:
The barrier layer is segmented into a first portion with reduced thickness (5-15 nm) located directly under the gate and a second portion with greater thickness (15-30 nm) in the drift region. This segmentation achieves threshold voltage control through reduced 2-DEG density under the gate while maintaining a simpler, more reproducible manufacturing process compared to traditional recessed-gate structures.
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 enables the production of normally-off devices with improved threshold voltage control and reduced on-resistance, simplifying the manufacturing process and enhancing the reproducibility of GaN-based power devices.
Implementation Method 1
a 2-dimensional electron gas (2-DEG) which is formed at the heterojunction between undoped GaN and undoped AlGaN
Implementation Method 2
the heterojunction between undoped GaN and undoped AlGaN
Data Source
AI summary
A semiconductor device is described. In one embodiment, the device includes a Group-III nitride channel layer and a Group-III nitride barrier layer on the Group-III nitride channel layer, wherein the Group-III nitride barrier layer includes a first portion and a second portion, the first portion having a thickness less than the second portion. A p-doped Group-III nitride gate layer section is arranged at least on the first portion of the Group-III nitride barrier layer and a gate contact formed on the p-doped Group-III nitride gate layer.