Nitride Semiconductor Device with Normally-Off HEMT Structure
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Solution Overview
Problem
Conventional high electron mobility transistors (HEMTs) with a GaN/AlGaN heterojunction structure are typically normally-on type, leading to safety concerns during abnormalities, and they exhibit high resistance to voltage and decreased high-frequency characteristics due to a short distance between the gate and drain electrodes, limiting their suitability for high-frequency and power devices.
Innovation Solution
A nitride semiconductor device with a heterojunction structure comprising a channel layer and a barrier layer, where a third nitride semiconductor layer with a smaller band gap than the channel layer is introduced between the source and drain electrodes, and a p-type conductivity layer is added to enhance the two-dimensional electron gas formation and control the current flow, allowing for a normally-off operation with increased gate-drain distance for higher voltage resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional GaN/AlGaN heterojunction structure is used to form a normally-on type HEMT, then the device can operate with high current and voltage capability, but the gate threshold voltage becomes negative causing safety issues during abnormalities
Solution Approach 1:
The patent applies local quality by creating a specific region (third nitride semiconductor layer with smaller band gap) between the source and drain that differs from the channel region. This localized structural modification enables normally-off characteristics in specific areas while preserving the overall device functionality and high current-voltage capability of the GaN/AlGaN heterojunction structure.
Solution Approach 2:
The patent uses composite materials by combining multiple nitride semiconductor layers with different band gap characteristics (GaN channel layer, AlGaN barrier layer, and third nitride semiconductor layer with smaller band gap). This composite structure allows simultaneous achievement of normally-off operation and high power handling capability through the synergistic effects of different material properties.
2Strength
If the distance between gate electrode and drain electrode is increased to improve voltage resistance, then the device can withstand higher voltages, but the gate length increases causing decreased high-frequency characteristics and switching speed
Solution Approach 1:
The patent resolves this contradiction by transitioning from a one-dimensional constraint (increasing gate-drain distance in the planar direction) to utilizing the vertical dimension (introducing a third nitride semiconductor layer with smaller band gap between source and drain). This dimensional change allows voltage resistance improvement without compromising switching speed or high-frequency characteristics.
Solution Approach 2:
The third nitride semiconductor layer acts as an intermediary element between the source and drain electrodes. This intermediate layer provides enhanced voltage resistance through its smaller band gap property while maintaining a compact structure that does not increase the gate length, thereby preserving fast switching performance.
3Strength
If the gate length is increased to improve voltage resistance, then the device can block higher voltages, but the gate capacity increases causing decreased high-frequency characteristics
Solution Approach 1:
The patent applies local quality by introducing a specific functional layer (third nitride semiconductor layer with smaller band gap) in the region between source and drain electrodes. This localized modification provides enhanced voltage blocking capability without requiring an increase in overall gate length, thereby maintaining good high-frequency characteristics.
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 solution enables a normally-off HEMT with improved high-frequency characteristics, high switching speed, and high voltage resistance, suitable for high-frequency and power devices by increasing the gate-drain distance without increasing the gate length, resulting in reduced ON resistance and enhanced carrier concentration.
Implementation Method 1
a high-density carrier layer called a two-dimensional carrier gas is formed by a polarization effect
Data Source
AI summary
A nitride semiconductor device includes: a main semiconductor region comprising a first nitride semiconductor layer having a first band gap, and a second nitride semiconductor layer having a second band gap larger than the first band gap, a heterojunction being formed between the first nitride semiconductor layer and the second nitride semiconductor layer such that a two-dimensional electron gas layer can be caused inside the first nitride semiconductor layer based on the heterojunction; a source electrode; a drain electrode; a third nitride semiconductor layer formed on the first nitride semiconductor layer and between the source electrode and the drain electrode; a fourth nitride semiconductor layer formed on the third nitride semiconductor layer and having p-type conductivity; and a gate electrode formed on the fourth nitride semiconductor layer. The third nitride semiconductor layer has a third band gap smaller than the first band gap.