GaN HEMT Current Collapse Mitigation via Undoped Spacer Layer
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Solution Overview
Problem
Conventional nitride semiconductor JFETs experience current collapse due to the close proximity of the two-dimensional electron gas layer to the surface, leading to decreased drain current when high drain voltages are applied, which is a significant issue for power transistors.
Innovation Solution
The introduction of an undoped or n-type semiconductor layer in regions excluding the gate electrode formation, increasing the distance between the surface and the two-dimensional electron gas layer, reduces the influence of surface-depletion layers and prevents current collapse by allowing a larger drain current and higher breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the AlGaN layer is thinned below the gate electrode to reduce 2DEG concentration for normally off operation, then the threshold voltage shifts to positive values, but the distance between the surface and the two-dimensional electron gas layer becomes small, leading to current collapse
Solution Approach 1:
The patent introduces a fourth semiconductor layer (undoped or n-type) between the third layer (p-type) and the surface, adding a new dimensional element to the structure. This additional layer increases the vertical distance between the surface and the two-dimensional electron gas layer, thereby reducing the influence of surface depletion layers and preventing current collapse while maintaining normally off operation.
2Ease of operation
If a p-type AlGaN layer is formed in the gate electrode region to raise potential energy and reduce 2DEG concentration, then normally off mode is achieved, but the surface proximity to the electron gas layer causes current collapse at high drain voltages
Solution Approach 1:
The fourth semiconductor layer acts as an intermediary between the third layer (p-type AlGaN) and the surface. This intermediate layer serves as a buffer that reduces the direct influence of surface effects on the two-dimensional electron gas layer, thereby preventing current collapse while allowing the p-type layer to maintain normally off operation.
3Reliability
If the distance between the surface and the two-dimensional electron gas layer is increased to prevent current collapse, then the device structure becomes more complex with additional layers
Solution Approach 1:
The patent modifies the structural parameters by introducing a fourth semiconductor layer with specific doping characteristics (undoped or n-type). This parameter change effectively increases the distance between the surface and the two-dimensional electron gas layer, preventing current collapse. The complexity increase is justified by the significant improvement in device reliability and performance.
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 effectively reduces or prevents current collapse, enabling nitride semiconductor devices to maintain high current density and breakdown voltage characteristics, making them suitable for power transistors.
Implementation Method 1
a third nitride semiconductor layer formed on the second nitride semiconductor layer and doped with a p-type impurity
Implementation Method 2
an undoped or n-type fourth nitride semiconductor layer formed on the third nitride semiconductor layer
Implementation Method 3
a heterojunction as with conventional arsenide-based semiconductor materials, such as GaAs and the like. The heterojunction provided by the nitride semiconductor (e.g., an AlGaN/GaN heterostructure) has a property that a high concentration of carriers which are generated by spontaneous polarization and piezoelectric polarization occur at the interface
Implementation Method 4
a high concentration of carriers which are generated by spontaneous polarization and piezoelectric polarization occur at the interface
Data Source
AI summary
A semiconductor device includes an undoped GaN layer (103) formed on a substrate (101), an undoped AlGaN layer (104) formed on the undoped GaN layer (103) and having a band gap energy larger than that of the undoped GaN layer (103), a p-type AlGaN layer (105) and a high-concentration p-type GaN layer (106) formed on the undoped AlGaN layer (104), and an n-type AlGaN layer (107) formed on the high-concentration p-type GaN layer (106). A gate electrode (112) which makes ohmic contact with the high-concentration p-type GaN layer (106) is formed on the high-concentration p-type GaN layer (106) in a region thereof exposed through an opening (107a) formed in the n-type AlGaN layer (107).