GaN HEMT Gate Stack Using p-InGaN for Higher Threshold Voltage
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Solution Overview
Problem
Gallium Nitride (GaN) High Electron Mobility Transistors (HEMTs) face a challenge in achieving high threshold voltage while maintaining high drain current, as increasing threshold voltage with low workfunction gate metals like tungsten results in significant reduction of drain current.
Innovation Solution
Incorporating a p-doped InGaN layer of at least 5 nm thickness between the AlGaN and p-doped gallium nitride layers, with a length greater than the gate stack, and an Mg doping concentration of at least 5×10^18 cm^-3, to increase threshold voltage and enhance hole injection, thereby raising the conduction band energy and increasing drain current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If tungsten gate metal is used to increase threshold voltage, then threshold voltage increases significantly, but drain current reduces significantly
Solution Approach 1:
The gate structure is segmented into multiple functional layers: a p-doped GaN layer for threshold voltage control and a p-doped InGaN layer for hole injection enhancement. This segmentation allows each layer to perform its specific function optimally, resolving the contradiction between high threshold voltage and high drain current by distributing the functional requirements across separate layers rather than relying on a single gate metal material.
Solution Approach 2:
The gate structure uses composite materials combining p-doped GaN and p-doped InGaN layers. The p-doped GaN provides the necessary threshold voltage while the p-doped InGaN enhances hole injection to maintain high drain current. This composite approach allows simultaneous achievement of high threshold voltage and high drain current that cannot be obtained with a single gate metal like tungsten.
2Device complexity
If normally on device structure is used, then device simplicity is maintained, but safety and system reliability are compromised
Solution Approach 1:
The device transitions from normally-on to normally-off operation by changing the threshold voltage parameter through the use of p-doped GaN and p-doped InGaN layers. The p-doping introduces positive charges that deplete the two-dimensional electron gas at the AlGaN/GaN interface, creating a normally-off characteristic. This parameter change enables safe operation while maintaining reasonable device complexity through controlled doping rather than complete structural redesign.
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 increases the threshold voltage while maintaining a relatively high drain current, balancing the need for high reliability and performance in power device applications.
Implementation Method 1
enhance hole injection, thereby raising the conduction band energy and increasing drain current
Implementation Method 2
raising the conduction band energy
Implementation Method 3
The p-doped GaN layer 316 and the p-doped InGaN layer 320 deplete the two-dimensional electron gas (2DEG) at the AlGaN/GaN interface
Data Source
AI summary
A transistor device including a layer of AlGaN extending between a source and drain of the device; a GaN channel layer extending under the AlGaN layer; a gate stack including a layer of p-doped gallium nitride; and a layer of p-doped InGaN of at least 5 nm in thickness positioned between the AlGaN layer and the p-doped gallium nitride layer, the InGaN layer having a length greater than a length of the gate stack.