HEMT Buffer Layer Grading for 2DEG Carrier Mobility
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Solution Overview
Problem
High Electron Mobility Transistors (HEMTs) face challenges in achieving optimal carrier density and mobility due to limitations in the formation of the Two-Dimensional Electron Gas (2DEG) layer, which affects their performance in high-frequency and high-power applications.
Innovation Solution
The method involves forming a HEMT structure using epitaxially grown III-V compound layers with specific band gaps and grading the aluminum and gallium content in buffer layers to create a 2DEG with high carrier mobility, including a buffer layer, a gallium nitride layer, an indium gallium nitride layer, and a donor-supply layer, along with a dielectric passivation and gate dielectric layer to enhance the transistor's performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional HEMT structures are used, then the device can be manufactured with standard processes, but the carrier density and mobility in the 2DEG layer are limited
Solution Approach 1:
The buffer layer is divided into multiple distinct layers with different compositions and functions: a first buffer layer, a second buffer layer with higher aluminum content, and a third buffer layer with graded composition. This segmentation allows each layer to optimize specific properties, resulting in improved carrier density and mobility in the 2DEG while managing the complexity through systematic layer design
Solution Approach 2:
Different regions of the buffer structure are given different aluminum indium nitride compositions tailored to local requirements. The graded buffer layer transitions from higher to lower aluminum content, creating localized optimization of strain and carrier concentration at different depths, which enhances overall 2DEG performance
2Reliability
If the aluminum content in buffer layers is increased to improve carrier confinement, then the 2DEG formation is enhanced, but the lattice mismatch and dislocation density increase
Solution Approach 1:
The aluminum content in the buffer layers is systematically varied through graded composition changes. The third buffer layer transitions from higher aluminum content near the 2DEG interface to lower aluminum content deeper in the layer, optimizing carrier confinement while progressively reducing lattice mismatch and dislocation density
Solution Approach 2:
The buffer structure uses composite aluminum indium nitride materials with varying compositions. By combining different aluminum and indium ratios in specific layers, the structure achieves both strong carrier confinement near the interface and reduced lattice mismatch in deeper regions, resolving the contradiction between confinement and defect reduction
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 results in a HEMT with high carrier density, low contact resistance, and high mobility, enabling better signal transmission and operation under higher voltages, as demonstrated by the comparison of band diagrams showing increased carrier mobility and reduced Ohmic contact resistance.
Implementation Method 1
A HEMT is a field effect transistor incorporating a very thin layer close to the junction between two materials with different band gaps (i.e., a heterojunction). The thin layer, instead of a doped region as is generally the case for Metal Oxide Semiconductor Field Effect Transistors (MOSFETs), acts as the channel.
Implementation Method 2
The method involves forming a HEMT structure using epitaxially grown III-V compound layers with specific band gaps
Implementation Method 3
grating the aluminum and gallium content in buffer layers to create a 2DEG with high carrier mobility
Data Source
AI summary
A High Electron Mobility Transistor (HEMT) includes a first III-V compound layer having a first band gap, and a second III-V compound layer having a second band gap over the first III-V compound layer. The second band gap is smaller than the first band gap. The HEMT further includes a third III-V compound layer having a third band gap over the second III-V compound layer, wherein the third band gap is greater than the first band gap. A gate electrode is formed over the third III-V compound layer. A source region and a drain region are over the third III-V compound layer and on opposite sides of the gate electrode.