E-mode HEMT Recessed Barrier for On-Current and Breakdown Voltage
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Solution Overview
Problem
Existing methods for manufacturing Enhancement-mode (E-mode) high electron mobility transistors (HEMTs) face challenges such as damage to the channel layer during recess formation and reduced on-current due to thin AlGaN barrier layers, which affect the insulation breakdown voltage and 2DEG concentration.
Innovation Solution
The proposed solution involves a double-layer barrier structure with a recessed region under the gate electrode, where the depletion layer covers the recess and extends around it, maintaining a 2DEG concentration and preventing channel layer damage, using a p-type semiconductor or dielectric depletion layer and varying barrier layer thicknesses to optimize 2DEG induction and on-current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a recess is formed in the AlGaN barrier layer to remove 2DEG below the gate electrode, then the HEMT operates in enhancement mode with increased insulation breakdown voltage, but the channel layer may be damaged during the recess formation process
Solution Approach 1:
A cladding layer is introduced as an intermediary between the AlGaN barrier layer and the channel layer. This cladding layer serves as a protective buffer during the recess formation process, preventing direct damage to the channel layer while allowing the AlGaN barrier layer to be etched back to form the enhancement mode structure.
2Reliability
If the AlGaN barrier layer thickness is reduced to remove 2DEG from below the gate electrode, then enhancement mode operation is achieved, but the 2DEG concentration in other regions of the channel layer is reduced and on-current decreases
Solution Approach 1:
The barrier layer thickness is made non-uniform through the recess structure, creating local variations in 2DEG concentration. The region outside the recess maintains sufficient barrier thickness to preserve high 2DEG concentration and on-current, while the recess region allows for proper gate control and enhancement mode operation.
Solution Approach 2:
The barrier layer is segmented into different thickness regions - a thicker region outside the recess that maintains high 2DEG concentration for current flow, and a thinner region within the recess that enables gate control. This segmentation allows simultaneous optimization of both on-current and enhancement mode operation.
3Reliability
If a p-GaN layer is formed between the gate electrode and AlGaN barrier layer to remove 2DEG, then enhancement mode operation is achieved, but the AlGaN barrier layer thickness is restricted and cannot be optimized
Solution Approach 1:
The p-GaN depletion layer is replaced by extracting the 2DEG through the recess method. This removes the constraint of requiring a specific p-GaN layer thickness and allows flexible optimization of the AlGaN barrier layer thickness to maximize 2DEG concentration and on-current while still achieving enhancement mode operation.
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 enhances the on-current and insulation breakdown voltage of E-mode HEMTs by maintaining 2DEG concentration without damaging the channel layer, improving the device's operational performance.
Implementation Method 1
The 2DEG arises due to a band gap and/or polarizability difference between two layers
Implementation Method 2
The 2DEG arises due to a band gap and/or polarizability difference between two layers
Implementation Method 3
a depletion layer disposed on the barrier layer between the source and drain electrodes
Data Source
AI summary
An Enhancement-mode (E-mode) high electron mobility transistor (HEMT) includes a channel layer with a 2-Dimensional Electron Gas (2DEG), a barrier layer inducing the 2DEG in the channel layer, source and drain electrodes on the barrier layer, a depletion layer on the barrier layer between the source and drain electrodes, and a gate electrode on the depletion layer. The barrier layer is recessed below the gate electrode and the depletion layer covers a surface of the recess and extends onto the barrier layer around the recess.