GaN Power Transistor with Recessed PN Junction Gate
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Solution Overview
Problem
Conventional power devices using AlGaN/GaN HEMTs face challenges in achieving normally-OFF operation with high current capability due to high threshold voltage and increased gate leak current, which limits their performance in power applications.
Innovation Solution
The semiconductor device incorporates a p-type nitride semiconductor layer with a recessed structure, a carrier supply layer having a greater bandgap, and a 2DEG layer formed between the third and fourth nitride semiconductor layers, allowing for a pn junction sandwiched between the gate electrode and the 2DEG layer, reducing 2DEG concentration and enhancing forward voltage, enabling normally-OFF and high-current operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a conventional AlGaN/GaN HEMT structure is used to achieve high current capability, then the current conduction is improved, but the gate leak current increases and normally-OFF operation becomes difficult
Solution Approach 1:
The gate structure is segmented into multiple functional layers: a p-type nitride semiconductor layer forming a pn junction with the channel layer, and a separate Schottky barrier gate electrode. This segmentation allows the pn junction to provide normally-OFF characteristics while the Schottky gate maintains high current capability, resolving the contradiction between current capability and gate leak current.
Solution Approach 2:
The p-type nitride semiconductor layer acts as an intermediary between the channel layer and the gate electrode. It forms a pn junction that depletes the 2DEG channel at zero gate bias, providing normally-OFF operation, while allowing controlled current flow when biased, thus mediating between the conflicting requirements of high current capability and low gate leak current.
2Speed
If the gate length is reduced to enable high-speed operation, then the operation speed is improved, but the control over 2DEG concentration becomes more difficult
Solution Approach 1:
The invention changes the fundamental parameter of gate control mechanism from direct electric field modulation in a short gate to pn junction depletion control. The pn junction provides strong depletion of the 2DEG channel through minority carrier injection, enabling effective control even with reduced gate length, thus achieving both high-speed operation and maintainable 2DEG control.
3Speed
If a short gate is used to achieve high-speed operation, then the operation speed is improved, but the forward voltage is reduced
Solution Approach 1:
The gate structure is segmented into a p-type nitride semiconductor layer that forms a pn junction and a separate Schottky barrier gate electrode. The pn junction provides forward voltage through its diode characteristics, while the Schottky gate maintains the short gate length for high-speed operation, thus resolving the contradiction between forward voltage and operation speed.
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 improves forward voltage, reduces gate leak current, and allows for both normally-OFF and high-current operations, while enabling a short gate length for high-speed performance, thus addressing the limitations of conventional power devices.
Implementation Method 1
a pn junction is formed between the p-type nitride semiconductor layer and the third nitride semiconductor layer
Implementation Method 2
a depletion layer (not shown) across a Schottky barrier, whereby a current in 2DEG layer 7 is controlled
Implementation Method 3
a high-concentration electron channel (two-dimensional electron gas which is referred to as 2DEG below) is generated in the GaN layer near an interface of the AlGaN/GaN layers due to piezoelectric charges generated from a difference in lattice constant between the AlGaN and the GaN layers, and a difference in bandgap between the AlGaN and the GaN layers
Implementation Method 4
Gate electrode 10 makes a Schottky contact with carrier supply layer 6
Implementation Method 5
a depletion layer (not shown) across a Schottky barrier, whereby a current in 2DEG layer 7 is controlled
Data Source
AI summary
A semiconductor device includes a substrate, a first nitride semiconductor layer formed on the substrate, a p-type nitride semiconductor layer formed on the first nitride semiconductor layer, a recess having a bottom portion which reaches the first nitride semiconductor layer through a part of the p-type nitride semiconductor layer, a third nitride semiconductor layer formed to cover the bottom portion of the recess, a side portion of the recess, and a part of an upper surface of the p-type nitride semiconductor layer. The semiconductor device further includes a fourth nitride semiconductor layer formed on the third nitride semiconductor layer, a first electrode formed on another side of the substrate, a gate electrode formed on the upper surface of the p-type nitride semiconductor layer, and a second electrode that is in contact with the third nitride semiconductor layer or the fourth nitride semiconductor layer. The third nitride semiconductor layer has a bandgap different from a bandgap of the fourth nitride semiconductor layer.