GaN Transistor Structure for Normally-Off Operation and High Drain Current
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Solution Overview
Problem
Conventional GaN-based nitride semiconductor transistors exhibit normally-on characteristics due to spontaneous and piezoelectric polarization, making it difficult to achieve normally-off characteristics with sufficient drain current.
Innovation Solution
A transistor structure with a p-type control region and a gate electrode that injects holes into the channel region, using materials with a larger band gap to enhance the potential barrier and increase electron concentration, allowing for normally-off operations with high drain current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional GaN-based nitride semiconductor FET is fabricated using undoped AlGaN/GaN heterojunction, then high-frequency and high-power characteristics are achieved, but the device exhibits normally-on characteristics due to polarization-induced carriers, making it difficult to achieve normally-off characteristics
Solution Approach 1:
The invention extracts and removes the harmful polarization-induced carriers from the channel by introducing a p-type control region that depletes these carriers, thereby achieving normally-off characteristics while maintaining the beneficial high-frequency and high-power properties of the AlGaN/GaN heterojunction structure
Solution Approach 2:
A p-type control region is introduced as an intermediary element between the source and drain, which mediates the channel conductivity by controlling the depletion of polarization-induced carriers through its forward bias, enabling normally-off operation
2Reliability
If the Al composition in the undoped AlGaN layer is decreased to reduce sheet carrier concentration, then normally-off characteristics become easier to achieve, but the operating current and forward voltage capability are significantly reduced
Solution Approach 1:
Instead of uniformly decreasing the Al composition throughout the AlGaN layer, the invention applies local quality control by introducing a p-type control region at specific locations, which selectively depletes carriers in the channel region while preserving the high Al composition needed for maintaining high operating current and forward voltage capability
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 structure enables a normally-off transistor with increased drain current and reduced leakage current, capable of applying higher forward voltages without significant gate leakage, addressing the limitations of conventional GaN-based transistors.
Implementation Method 1
the gate electrode is forward biased with respect to the source electrode to inject holes into the channel region
Implementation Method 2
injecting holes to enhance electron generation in the channel
Implementation Method 3
using materials with a larger band gap to enhance the potential barrier and increase electron concentration, while suppressing leakage current
Implementation Method 4
spontaneous polarization or piezoelectric polarization in the film constituting the junction generates high concentrations of carriers at its heterointerface
Implementation Method 5
spontaneous polarization or piezoelectric polarization in the film constituting the junction generates high concentrations of carriers at its heterointerface
Data Source
AI summary
In a transistor, an AlN buffer layer 102, an undoped GaN layer 103, an undoped AlGaN layer 104, a p-type control layer 105, and a p-type contact layer 106 are formed in this order on a sapphire substrate 101. The transistor further includes a gate electrode 110 in ohmic contact with the p-type contact layer 106, and a source electrode 108 and a drain electrode 109 provided on the undoped AlGaN layer 104. By applying a positive voltage to the p-type control layer 105, holes are injected into a channel to increase a current flowing in the channel.