Carbon-Doped AlN Seed Layer for High-Voltage HEMT Stability
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Solution Overview
Problem
High electron mobility transistors (HEMTs) face challenges in high voltage applications due to electron injection and silicon diffusion, leading to performance degradation over time, and there is a need for improved lattice matching and doping strategies to enhance their operational capabilities.
Innovation Solution
A semiconductor structure comprising a doped substrate, a carbon-doped seed layer with multiple AlN sublayers, a graded layer with varying Al:Ga ratios, and an active layer to form a two-dimensional electron gas (2-DEG), which reduces electron injection and silicon diffusion, enabling higher voltage applications while minimizing material waste and production costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional HEMT structures are used for high voltage applications, then device performance degrades over time due to electron injection and silicon diffusion, but modifying the structure to prevent these issues increases manufacturing complexity
Solution Approach 1:
The seed layer is divided into multiple sublayers (first seed sublayer, second seed sublayer, third seed sublayer) with different compositions and functions. Each sublayer addresses specific issues: the first AlN sublayer provides lattice matching, the second GaN sublayer serves as a diffusion barrier, and the third AlN sublayer enhances electron mobility. This segmentation resolves the contradiction by distributing the protective functions across multiple specialized layers rather than requiring a single complex structure.
Solution Approach 2:
The invention uses composite material structures including AlN-GaN alternating layers in the seed region and AlGaN graded layers with varying composition ratios. These composite structures combine the advantages of different materials: AlN provides high breakdown voltage and lattice matching, while GaN provides high electron mobility and silicon diffusion resistance. The composite approach achieves high reliability without excessive structural complexity.
2Manufacturing precision
If a graded layer with varying Al:Ga ratios is implemented to improve lattice matching, then manufacturing precision requirements increase, but this enables better device performance
Solution Approach 1:
The graded layer implements gradual parameter changes by varying the Al:Ga ratio from the first AlGaN layer through the second AlGaN layer to the third AlGaN layer. Each subsequent layer has a progressively changing composition that bridges the lattice mismatch between the GaN buffer and the AlN cap layer. This gradual parameter transition reduces dislocation density and improves lattice matching, enabling high device performance while managing manufacturing precision requirements through systematic composition gradients.
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 proposed structure allows HEMTs to operate effectively at higher voltages with reduced inversion current and silicon diffusion, enhancing their performance and reliability in high voltage applications while optimizing production efficiency.
Implementation Method 1
A buffer layer is provided over the silicon substrate. The buffer layer includes a first buffer sublayer, a second buffer sublayer, and a third buffer sublayer. Each buffer sublayer includes alternating layers of GaN and AlN. The alternating layers of GaN and AlN reduce inversion current and reduce diffusion of silicon from the silicon substrate into the active layer.
Implementation Method 2
The graded buffering reduces misfit dislocation. The active layer is provided over the buffer layer. The active layer includes alternating layers of AlN and AlGaN. Each AlGaN layer has a different aluminum to gallium ratio, wherein the AlGaN layer furthest from the silicon substrate has the highest aluminum to gallium ratio.
Data Source
AI summary
A semiconductor device includes a substrate and a seed layer over the substrate. The seed layer includes a first seed sublayer having a first lattice structure, wherein the first seed sublayer includes AlN, and the first seed sublayer is doped with carbon, and a second seed sublayer over the first seed layer, wherein the second seed layer has a second lattice structure different from the first lattice structure, and a thickness of the second seed sublayer ranges from about 50 nanometers (nm) to about 200 nm. The semiconductor device further includes a graded layer over the seed layer. The graded layer includes a first graded sublayer including AlGaN, having a first Al:Ga ratio; and a second graded sublayer over the first graded sublayer, wherein the second graded sublayer includes AlGaN having a second Al:Ga ratio. The semiconductor device further includes a two-dimensional electron gas (2-DEG) over the graded layer.