GaN FET Diffusion Suppression Layer for Normally-Off Operation
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Solution Overview
Problem
GaN-based nitride semiconductor devices face challenges in achieving a normally-off type FET due to high contact and sheet resistance caused by p-type dopant diffusion, which affects the device's performance and reliability.
Innovation Solution
Incorporating a diffusion suppression layer between the barrier layer and the p-type conductive layer to reduce p-type dopant diffusion, thereby suppressing the change of the barrier layer into a p-type and minimizing contact and sheet resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a p-type GaN layer is provided in a gate formation region to cancel piezoelectric polarization and reduce 2DEG, then a normally-off characteristic is achieved, but contact resistance and sheet resistance increase due to p-type dopant diffusion into the barrier layer
Solution Approach 1:
An undoped GaN layer is introduced as an intermediary between the AlGaN barrier layer and the p-type GaN layer. This intermediary layer prevents direct contact between the barrier layer and p-type dopant source, thereby blocking dopant diffusion while maintaining the piezoelectric polarization cancellation effect that enables normally-off operation.
Solution Approach 2:
The structure is segmented into distinct functional layers: an AlGaN barrier layer for piezoelectric polarization, an undoped GaN layer for dopant isolation, and a p-type GaN layer for piezoelectric polarization cancellation. This segmentation allows each layer to perform its specific function without interfering with others, solving the contradiction between achieving normally-off characteristic and preventing dopant diffusion.
2Reliability
If p-type dopant is introduced into the barrier layer to cancel piezoelectric polarization, then normally-off type FET is achieved, but the barrier layer changes into p-type causing increased contact resistance
Solution Approach 1:
The undoped GaN layer serves as a protective intermediary that prevents p-type dopant from reaching and changing the electrical properties of the AlGaN barrier layer. This allows the barrier layer to maintain its original n-type characteristics and low contact resistance while still achieving normally-off operation through piezoelectric polarization cancellation in the p-type layer.
3Reliability
If p-type dopant diffuses into the barrier layer, then piezoelectric polarization cancellation occurs, but sheet resistance increases due to reduced carrier concentration
Solution Approach 1:
The structure separates the piezoelectric polarization cancellation function (performed by the p-type GaN layer) from the low-resistance conduction function (maintained by the undoped GaN layer beneath it). This segmentation allows piezoelectric polarization cancellation to occur without compromising the carrier concentration and sheet resistance in the barrier layer.
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 configuration effectively reduces contact and sheet resistance, enhancing the device's performance by maintaining the normally-off state and improving carrier mobility and dielectric breakdown voltage.
Implementation Method 1
p-type dopant diffusion
Implementation Method 2
high concentration carriers generated by spontaneous polarization or piezoelectric polarization
Data Source
AI summary
A semiconductor device includes: a channel layer which is made of InpAlqGa1-p-qN (0≦p+q≦1, 0≦p, and 0≦q); a barrier layer which is formed on the channel layer and is made of InrAlsGa1-r-sN (0≦r+s≦1, 0≦r) having a bandgap larger than that of the channel layer; a diffusion suppression layer which is selectively formed on the barrier layer and is made of IntAluGa1-t-uN (0≦t+u≦1, 0≦t, and s>u); a p-type conductive layer which is formed on the diffusion suppression layer and is made of InxAlyGa1-x-yN (0≦x+y≦1, 0≦x, and 0≦y) having p-type conductivity; and a gate electrode which is formed on the p-type conductive layer.