P-Type Schottky GaN Gate Structure for Breakdown-Resistant HEMTs
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Solution Overview
Problem
Group III nitride-based transistor devices with p-type Schottky gates face reliability issues due to time-dependent dielectric breakdown, where injected electrons from the two-dimensional electron gas can accelerate to high energies and cause defects and junction breakdown in the Schottky depletion region.
Innovation Solution
Incorporating one or more p-doped AlxGa(1-x)N layers within the p-doped Group III nitride structure of the p-type Schottky gate to prevent injected electrons from reaching the Schottky depletion region, allowing them to recombine in the lower p-doped GaN layer, thereby improving gate reliability and reducing electron gate current while maintaining hole current integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a p-type Schottky gate with a p-doped Group III nitride layer is used, then the transistor device can be fabricated with simpler structure, but the gate reliability is limited by time-dependent dielectric breakdown
Solution Approach 1:
The p-doped Group III nitride layer is segmented into multiple layers with different doping concentrations and compositions. The p-doped AlxGa1-xN layer is positioned between the metal gate and the p-doped GaN layer, creating a graded structure that reduces electric field intensity at critical interfaces while maintaining the overall p-type Schottky gate functionality.
Solution Approach 2:
The gate structure employs composite materials by combining p-doped GaN with p-doped AlxGa1-xN layers. This composite structure leverages the beneficial properties of both materials: GaN provides high breakdown voltage while AlGaN reduces electric field intensity, together enhancing gate reliability without significantly increasing structural complexity.
2Productivity
If electrons are injected from the two-dimensional electron gas into the p-doped Group III nitride layer, then the transistor device can operate in on state, but the injected electrons can accelerate to very high energies and cause defects and junction breakdown
Solution Approach 1:
The p-doped AlxGa1-xN layer serves as an intermediary between the two-dimensional electron gas and the Schottky depletion region. This intermediate layer has optimized doping concentration and composition that facilitate electron recombination through trap states while preventing electrons from gaining sufficient energy to cause damage in the high-field depletion region.
Solution Approach 2:
The doping concentration and composition parameters are changed across different layers. The p-doped AlxGa1-xN layer has different doping concentration (10^19 to 10^21 atoms/cm³) and aluminum content (x=0.1 to 0.4) compared to the p-doped GaN layer, creating a gradient that modifies electron transport and recombination characteristics to reduce harmful high-energy electron effects.
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 introduction of p-doped AlxGa(1-x)N layers enhances the gate lifetime by preventing electron injection into the Schottky depletion region, reducing electron gate current, and minimizing threshold voltage variations, thus improving the overall reliability and performance of the transistor device.
Implementation Method 1
The structure provided herein encourages the injected electrons to recombine in the lower p-doped Group III nitride region that comprises GaN and that is arranged between the p-doped AlxGa(1-x)N layer and the Group III nitride body
Implementation Method 2
the Group III nitride-based body has a multilayer structure having a heterojunction that is capable of supporting a two-dimensional electron gas (2DEG) which forms the channel of the transistor device
Implementation Method 3
If these injected electrons reach the high field Schottky depletion region, they can be accelerated to very high energies which leads to the creation of defects and junction breakdown
Data Source
AI summary
In an embodiment, a Group III nitride-based transistor device is provided that includes a Group III nitride-based body and a p-type Schottky gate including a metal gate on a p-doped Group III nitride structure. The p-doped Group III nitride structure includes an upper p-doped GaN layer in contact with the metal gate and having a thickness d1, a lower p-doped Group III nitride layer having a thickness d2 and including p-doped GaN that is arranged on and in contact with the Group III nitride-based body, and at least one p-doped AlxGa1-xN layer arranged between the upper p-doped GaN layer and the lower p-doped Group III nitride layer, wherein 0<x<1. The thickness d2 of the lower p-doped Group III nitride layer is larger than the thickness d1 of the upper p-doped GaN layer.