GaN Drift Layer Gradient for High Breakdown Voltage
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Solution Overview
Problem
In nitride semiconductor devices, particularly power and high-frequency devices, the low donor concentration in the drift layer leads to inadequate free electron concentration due to carbon incorporation, compromising device performance.
Innovation Solution
A nitride semiconductor substrate with a gallium nitride drift layer having a donor concentration of 5.0×10^16/cm^3 or less, where the donor concentration is greater than the carbon acceptor concentration, and the difference between the two is gradually decreased from the substrate side to the surface side, ensuring a desired free electron distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the donor concentration in the drift layer is reduced to improve breakdown voltage, then the breakdown voltage is improved, but the free electron concentration becomes inadequate due to carbon compensation
Solution Approach 1:
The patent applies local quality by creating a drift layer with spatially varying donor and carbon concentrations. The donor concentration decreases from 5.0×10^16/cm³ or less near the substrate toward the surface, while the carbon concentration also varies spatially. This local variation in composition allows the drift layer to simultaneously achieve high breakdown voltage (through low overall donor concentration) and adequate free electron concentration (through controlled carbon distribution that minimizes compensation effects in critical regions).
Solution Approach 2:
The patent employs parameter changes by precisely controlling the donor concentration to be 5.0×10^16/cm³ or less and managing the carbon concentration distribution throughout the drift layer. By adjusting these compositional parameters during crystal growth and creating a gradient structure, the patent resolves the contradiction between achieving high breakdown voltage (requiring low donor concentration) and maintaining sufficient free electron concentration (compromised by carbon acceptance).
2Strength
If the donor concentration is kept low to improve breakdown voltage, then the breakdown voltage improves, but device performance deteriorates due to insufficient free electron concentration
Solution Approach 1:
The patent implements local quality by establishing a drift layer where donor and carbon concentrations vary spatially from the substrate side toward the surface. The donor concentration is maintained at 5.0×10^16/cm³ or less overall, with a gradient distribution that ensures adequate free electron concentration in regions critical for device performance while maintaining low average concentration for high breakdown voltage.
Solution Approach 2:
The patent applies composite materials principles by creating a drift layer that is a composite structure with controlled distributions of donors and carbon atoms within the gallium nitride crystal lattice. This composite approach, achieved through specific crystal growth techniques, allows the material to exhibit both high breakdown voltage characteristics (from low overall donor concentration) and sufficient electrical conductivity (from optimized free electron concentration through controlled carbon distribution).
Data Source
AI summary
There is provided a nitride semiconductor substrate, including: a substrate configured as an n-type semiconductor substrate; and a drift layer provided on the substrate and configured as a gallium nitride layer containing donors and carbons, wherein a concentration of the donors in the drift layer is 5.0×1016/cm3 or less, and is equal to or more than a concentration of the carbons that function as acceptors in the drift layer, over an entire area of the drift layer, and a difference obtained by subtracting the concentration of the carbons that function as acceptors in the drift layer from the concentration of the donors in the drift layer, is gradually decreased from a substrate side toward a surface side of the drift layer.