Group IIIA-N HEMT Gate Stack with Tunnel Diode
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Solution Overview
Problem
E-mode Group IIIA-N HEMTs using Mg doped GaN layers for p-GaN exhibit poor doping efficiency due to the deep nature of Mg as a dopant, leading to low electrical conductivity and difficulties in forming uniform low-resistance gate contacts, which are typically achieved with metals like Pd, Ni, and ITO not available in silicon-based fabrication facilities.
Innovation Solution
Incorporating a tunnel diode in the gate stack of E-mode Group IIIA-N HEMTs allows for the use of n-type contacts instead of p-type contacts, utilizing conventional metals like Ti or Al, and employing an InGaN layer to independently adjust the threshold voltage without increasing on-resistance, thereby simplifying the fabrication process and improving contact uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Mg doped GaN layer is used for p-GaN to provide enhancement-mode operation, then threshold voltage control is achieved, but doping efficiency is poor and electrical conductivity is low
Solution Approach 1:
An InGaN layer is introduced as an intermediary between the p-GaN layer and the barrier layer. This InGaN layer serves as a mediator that enables effective tunneling contact while allowing the Mg doped p-GaN layer to maintain its threshold voltage control function, thus resolving the contradiction between achieving enhancement-mode operation and maintaining good doping efficiency.
Solution Approach 2:
The gate stack is segmented into multiple functional layers: the p-GaN layer for threshold voltage control, the InGaN layer for tunneling contact, and the barrier layer for channel formation. This segmentation allows each layer to optimize its specific function, with the InGaN layer specifically addressing the conductivity issue without compromising the p-GaN layer's threshold voltage control.
2Reliability
If high concentrations of Mg are used to generate sufficient hole densities, then threshold voltage control is improved, but series gate resistance increases
Solution Approach 1:
The InGaN layer acts as a tunneling mediator that provides a low-resistance path for gate current, decoupling the threshold voltage control function (performed by the p-GaN layer) from the conductivity requirement. This allows high Mg concentrations to be used for effective threshold voltage control without suffering from high series gate resistance.
Solution Approach 2:
The introduction of the InGaN layer changes the electrical parameters of the gate stack by providing a tunneling pathway with different resistance characteristics. This parameter change allows the system to achieve both high threshold voltage control (through Mg doping in p-GaN) and low series gate resistance (through tunneling in InGaN).
3Ease of manufacture
If conventional gate electrode materials are used, then fabrication complexity is reduced, but contact resistance to p-GaN layer increases
Solution Approach 1:
The InGaN layer serves as a universal intermediary that enables conventional gate electrode materials to form low-resistance contacts. Instead of requiring specialized p-type contact materials, the InGaN tunneling layer provides a compatible interface for standard metals, thus resolving the contradiction between fabrication simplicity and contact resistance.
4Manufacturing precision
If InGaN layer is added to enable tunneling, then doping efficiency is improved, but device structure becomes more complex
Solution Approach 1:
The gate stack is divided into distinct functional segments (p-GaN for threshold control, InGaN for tunneling contact, barrier layer for channel formation), allowing each to be optimized independently. The InGaN layer, while adding structural complexity, provides a specialized function that resolves the doping efficiency issue without requiring fundamental redesign of the entire device.
Solution Approach 2:
The gate stack employs a composite structure combining p-GaN and InGaN layers, each with complementary properties. The p-GaN provides threshold voltage control while the InGaN provides tunneling contact, creating a composite system that achieves both functions with improved overall performance despite increased structural complexity.
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 approach enables the use of conventional gate electrode materials, reduces series gate resistance, and allows for independent control of threshold voltage without affecting on-resistance, facilitating the integration of E-mode HEMTs with different voltage thresholds on the same die.
Implementation Method 1
Incorporating a tunnel diode in the gate stack of E-mode Group IIIA-N HEMTs allows for the use of n-type contacts instead of p-type contacts
Implementation Method 2
InGaN is recognized to be capable of having a narrower bandgap compared to GaN, and more importantly to provide built-in polarization fields that help create a band offset in a much thinner layer
Data Source
AI summary
One example provides an enhancement-mode High Electron Mobility Transistor (HEMT) includes a substrate, a Group IIIA-N active layer over the substrate, a Group IIIA-N barrier layer over the active layer, and at least one isolation region through the barrier layer to provide an isolated active area having the barrier layer on the active layer. A gate stack is located between source and drain contacts to the active layer. A tunnel diode in the gate stack includes an n-GaN layer on an InGaN layer on a p-GaN layer located on the barrier layer.