Ge-Doped N-Type GaN Substrate for Uniform High Carrier Density
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Solution Overview
Problem
Existing GaN substrates doped with Si as a donor impurity face issues of fragility and large variations in in-plane carrier concentration distribution, which are not adequately addressed by Ge-doped substrates as described in WO 2020/036047.
Innovation Solution
The development of an n-type GaN substrate doped with Ge as a donor impurity, featuring a high average carrier concentration of 1×10^18 cm^-3 or more, with a highly uniform in-plane carrier concentration distribution achieved by controlling the growth process to suppress hillock formation and ensuring specific conditions on measurement points, such as standard deviation/average ≤ 0.25, and ratios of carrier concentrations within defined regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Si is used as a donor impurity to achieve high carrier concentration, then the carrier concentration increases, but the substrate becomes fragile and SiN film forms during crystal growth
Solution Approach 1:
The patent changes the dopant type from Si to Ge, which fundamentally alters the doping parameters. Ge doping achieves high carrier concentration (≥1×10^18 cm^-3) without forming SiN films during crystal growth, thereby eliminating the fragility issue while maintaining the desired electrical properties
Solution Approach 2:
The patent replaces Si with Ge as the donor impurity. Although Ge is more expensive than Si, it eliminates the formation of harmful SiN films and substrate fragility, providing a more reliable long-term solution for high carrier concentration applications
2Reliability
If Ge is used as a donor impurity to avoid SiN film formation, then substrate fragility is reduced, but large variation in in-plane carrier concentration distribution occurs
Solution Approach 1:
The patent specifies precise measurement conditions and evaluation criteria for carrier concentration uniformity. By defining specific measurement lines (A and B) passing through the substrate center and establishing quantitative thresholds (standard deviation/average ≤ 0.25), the patent creates localized quality standards to evaluate and ensure uniform Ge distribution
Solution Approach 2:
The patent establishes feedback mechanisms through defined measurement protocols and evaluation criteria. By measuring carrier concentration at multiple points along specific lines and comparing against predetermined thresholds, the manufacturing process can be adjusted to maintain uniform Ge doping distribution
3Quantity of substance
If high-concentration doping is applied to achieve high carrier concentration, then the carrier concentration increases, but large variation in in-plane carrier concentration distribution results
Solution Approach 1:
The patent changes the dopant from Si to Ge, which has different diffusion and distribution characteristics. This parameter change enables achieving high carrier concentration (≥1×10^18 cm^-3) while maintaining better in-plane uniformity, as Ge distributes more evenly during crystal growth compared to Si
Solution Approach 2:
The patent implements localized measurement and evaluation at multiple points along defined lines through the substrate. By establishing quantitative criteria (standard deviation/average ≤ 0.25) and measuring at specific locations, the patent ensures local quality control to maintain overall uniformity even at high doping concentrations
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 resulting GaN substrate exhibits a high carrier concentration with minimal in-plane variation, suitable for use in laser diodes and vertical GaN power devices, ensuring consistent performance and reliability.
Implementation Method 1
The n-type GaN substrate contains Ge as a donor impurity
Data Source
AI summary
An n-type GaN substrate having two main surfaces, the n-type GaN substrate being doped with Ge, having an average carrier concentration of 1×1018 cm−3 or more, and satisfying at least one selected from the group consisting of (1) to (3) when carrier concentrations are measured at measurement points uniformly provided in a circular region having a radius of 15 mm from the center of at least one main surface: (1) a standard deviation/average of measured values at measurement points on straight lines passing through the center of the main surface in directions of 0 degrees, 45 degrees, 90 degrees, and 135 degrees is 0.25 or less; (2) the ratio of the number of measurement points at which a carrier concentration is 2×1018 cm−3 or more to the total number of the measurement points is 90% or more; and (3) the ratio of the number of measurement points at which a measured value is (A) 60% or less/(B) 50% or less/(C) 40% or less of the maximum of measured values at all measurement points to the total number of the measurement points is (A) 10% or less/(B) 9% or less/(C) 8% or less. The n-type GaN substrate has a high carrier concentration and a uniform in-plane carrier concentration distribution.