Patterned Back-Barrier for GaN HEMT Electric Field Control
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Solution Overview
Problem
GaN-based HEMTs with uniform AlGaN back-barriers face performance degradation due to increased device capacitance and risk of spurious turn-on effects from hole accumulation, which reduces the effectiveness of electric field reduction and increases the Al content's marginal benefits.
Innovation Solution
A patterned III-nitride back-barrier is buried in the III-nitride buffer, extending laterally beyond the gate towards the drain, with controlled thickness, length, Al content, and vertical spacing to reduce electric field buildup without degrading device performance, utilizing a different band gap to create a two-dimensional charge carrier gas channel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If uniform AlGaN back-barrier is used to reduce electric field, then hole accumulation reduces maximum electric field, but device capacitance increases and performance degrades
Solution Approach 1:
The uniform back-barrier is segmented into a patterned structure with alternating high-Al-content AlGaN regions and low-Al-content AlGaN regions. This segmentation allows the high-Al regions to provide strong hole accumulation for electric field reduction while the low-Al regions maintain thinner effective buffer thickness, thereby reducing device capacitance and resolving the contradiction between electric field reduction and capacitance control.
Solution Approach 2:
Different regions of the back-barrier are assigned different Al contents to perform different functions: high-Al-content regions (30-50%) provide hole accumulation for electric field shielding, while low-Al-content regions (3-4%) maintain low capacitance. This local quality differentiation resolves the contradiction by optimizing each region's contribution to either electric field reduction or capacitance control.
2Reliability
If Al content in back-barrier is increased to reduce electric field, then electric field reduction improves, but device capacitance increases and performance degrades
Solution Approach 1:
The back-barrier is divided into functional segments with different Al contents. High-Al segments provide the necessary hole accumulation for electric field reduction, while low-Al segments prevent excessive capacitance increase. This segmentation enables achieving electric field reduction without the performance degradation that would result from uniformly increasing Al content throughout the back-barrier.
Solution Approach 2:
The back-barrier exhibits local quality variations in Al content, with high-Al regions (30-50%) positioned to maximize hole accumulation for electric field reduction, and low-Al regions (3-4%) positioned to minimize capacitance impact. This local optimization resolves the contradiction between improving electric field reduction and maintaining device performance.
3Reliability
If uniform AlGaN back-barrier is used for normally-off device concepts, then threshold voltage increases due to quantum confinement, but device capacitance increases
Solution Approach 1:
The patterned back-barrier segments the quantum confinement effect spatially. High-Al regions provide strong confinement for threshold voltage control, while low-Al regions minimize capacitance contribution. This segmentation allows achieving normally-off characteristics with reduced capacitance compared to uniform back-barrier designs.
Solution Approach 2:
Different regions of the back-barrier provide different contributions to quantum confinement and capacitance. High-Al regions (30-50%) enhance threshold voltage through quantum confinement, while low-Al regions (3-4%) keep capacitance low. This local quality differentiation resolves the contradiction between threshold voltage control and capacitance management in normally-off devices.
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 patterned back-barrier effectively reduces the maximum electric field and leakage current while maintaining device reliability and performance by acting as a back field-plate and pulling up the conduction band to confine electrons, offering improved reliability and reduced capacitance.
Implementation Method 1
The III-nitride barrier has a different band gap than the III-nitride buffer so that a two-dimensional charge carrier gas channel arises along an interface between the III-nitride buffer and the III-nitride barrier
Implementation Method 2
The reduction of the maximum electric field in presence of a uniform AlGaN back-barrier is mainly due to hole accumulation in off-state conditions. Accumulated holes effectively act as a back field-plate which shields the high voltage applied at the drain side and dramatically reduces the electric field in the gate region
Implementation Method 3
Uniform AlGaN back-barriers also have been used in conjunction with normally-off device concepts, with the additional purpose of increasing the device threshold voltage as an effect of the additional quantum confinement of carriers between the main AlGaN barrier and the AlGaN back-barrier
Data Source
AI summary
A compound semiconductor device includes a III-nitride buffer and a III-nitride barrier on the III-nitride buffer. The III-nitride barrier has a different band gap than the III-nitride buffer so that a two-dimensional charge carrier gas channel arises along an interface between the III-nitride buffer and the III-nitride barrier. The compound semiconductor device further includes a source and a drain spaced apart from one another and electrically connected to the two-dimensional charge carrier gas channel, a gate for controlling the two-dimensional charge carrier gas channel between the source and the drain, and a patterned III-nitride back-barrier buried in the III-nitride buffer. The patterned III-nitride back-barrier extends laterally beyond the gate towards the drain and terminates prior to the drain so that the patterned III-nitride back-barrier is laterally spaced apart from the drain by a region of the III-nitride buffer.