GaN HEMT Buffer Doping Gradient for Current Collapse Reduction
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Solution Overview
Problem
GaN-based HEMT devices face issues such as current collapse, degraded 2DEG confinement, and high dislocation density due to low-quality carbon-doped GaN buffers, which are caused by low growth temperature, pressure, and high growth rate conditions leading to electron traps and carbon diffusion.
Innovation Solution
A linear carbon doping gradient is introduced in the upper portion of the c-GaN buffer layer by combining intrinsic and extrinsic carbon doping, using hexene as the extrinsic dopant, to improve the quality of the u-GaN channel and enhance 2DEG confinement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If low growth temperature, pressure, and high growth rate conditions are used to form carbon-doped GaN buffer, then the buffer formation speed increases, but current collapse, degraded 2DEG confinement, and high dislocation density occur
Solution Approach 1:
The patent applies parameter changes by implementing a graded carbon doping concentration profile in the GaN buffer layer, where the carbon doping concentration decreases from the substrate interface toward the channel layer. This gradient structure allows the buffer to maintain high growth rate conditions while reducing carbon diffusion and electron traps in the upper regions, thereby resolving the contradiction between formation speed and device performance
Solution Approach 2:
The patent applies local quality by creating different carbon doping concentrations at different depths within the buffer layer. The lower portion near the substrate has higher carbon concentration for buffer quality, while the upper portion near the channel has lower carbon concentration to prevent carbon diffusion and electron traps, thus achieving both high growth rate and good device performance in different regions
2Reliability
If high carbon doping concentration is used in GaN buffer, then buffer quality improves, but carbon diffusion increases causing current collapse
Solution Approach 1:
The patent changes the carbon doping concentration parameter from uniform to graded, creating a gradient that decreases from the substrate interface toward the channel layer. This parameter change allows high carbon concentration near the substrate for buffer quality while reducing carbon concentration in upper regions to minimize carbon diffusion and current collapse
Solution Approach 2:
The patent introduces a depth dimension to the carbon doping profile, transforming from a two-dimensional uniform doping approach to a three-dimensional graded doping approach. This dimensional change enables spatial control of carbon concentration, achieving high buffer quality at the substrate interface while preventing carbon diffusion toward the channel region
3Ease of manufacture
If low quality carbon-doped GaN buffer is used, then manufacturing is easier, but dislocation density increases and 2DEG confinement degrades
Solution Approach 1:
The patent applies parameter changes by implementing a graded carbon doping profile that can be achieved through controlled growth conditions. This approach maintains ease of manufacture through standard growth techniques while achieving low dislocation density and good 2DEG confinement through the optimized carbon concentration gradient
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 carbon doping gradient effectively reduces current collapse effects and dislocation density, improving the performance of GaN-based HEMT devices by compensating electron traps and enhancing gate control.
Implementation Method 1
doping a first thickness of gallium nitride (GaN) with a first concentration of dopant, and doping a second thickness of GaN with a second concentration of the dopant such that the second concentration of dopant has a gradient though the second thickness
Data Source
AI summary
A method of manufacturing a High-Electron-Mobility Transistor (HEMT) includes: preparing a substrate; forming a first buffer over the substrate; forming a second buffer over the first buffer, wherein forming the second buffer includes doping a first thickness of a material such as gallium nitride (GaN) with a first concentration of a dopant such as carbon, and doping a second thickness of the material with a second concentration of the dopant such that the second concentration of dopant has a gradient though the second thickness which progressively decreases in a direction away from the first thickness; forming a channel layer such as a GaN channel over the second buffer; forming a barrier layer such as aluminum gallium nitride (AlGaN) over the channel layer; and forming drain, source and gate terminals for the HEMT.