Oxygen-Doped Ammonothermal GaN Crystals With Low Dislocation Density
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Solution Overview
Problem
Current methods for growing n-type gallium-containing nitride crystals face challenges in achieving low-cost, high-quality substrates with optimal crystallographic and electrical properties, as conventional techniques like MOCVD and HVPE result in high dislocation densities and expensive substrates with poor performance.
Innovation Solution
The ammonothermal method is used to synthesize n-type gallium-containing nitride crystals with controlled dopant and impurity concentrations, specifically targeting the compensation ratio and infrared absorption features to achieve desired electrical properties, utilizing supercritical ammonia and precise temperature and pressure conditions to produce crystals with improved transparency and mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional MOCVD method is used to deposit GaN, then deposition can be performed from ammonia and organometallic compounds, but growth rates are slow and dislocation densities are high
Solution Approach 1:
The patent changes the fundamental growth parameters by using ammonothermal method instead of MOCVD, operating at high temperature (900-1100°C) and high pressure (50-200 atm) with supercritical ammonia as solvent, which enables both high growth rates and low dislocation densities simultaneously
Solution Approach 2:
The patent introduces supercritical ammonia as an intermediary solvent medium that facilitates GaN crystal growth from polycrystalline nutrients, enabling controlled deposition with high purity and low defect density while achieving high growth rates
2Reliability
If HVPE method is used to grow GaN substrates, then n-type substrates with good electrical properties can be obtained, but substrates are expensive and have high threading dislocation densities
Solution Approach 1:
The patent uses inexpensive polycrystalline GaN nutrients as sacrificial material that dissolves in supercritical ammonia to provide Ga source for crystal growth, replacing expensive HVPE processes while maintaining good electrical properties through controlled oxygen doping
Solution Approach 2:
The patent modifies growth parameters by controlling temperature (900-1100°C), pressure (50-200 atm), and oxygen content in supercritical ammonia to achieve n-type conductivity with compensation ratio <4.0, providing cost-effective alternative to HVPE
3Reliability
If HVPE GaN substrates are used, then n-type electrical properties can be achieved, but threading dislocation densities are high (10^6-10^7 cm^-2)
Solution Approach 1:
The patent uses supercritical ammonia as intermediary solvent that enables controlled dissolution of polycrystalline nutrients and sequential crystallization on seed substrates, producing high-quality epitaxial layers with low dislocation densities while maintaining n-type electrical properties
Solution Approach 2:
The patent optimizes growth parameters including temperature (900-1100°C), pressure (50-200 atm), and oxygen concentration in supercritical ammonia to achieve simultaneous reduction of dislocation density and control of electrical properties
4Manufacturing precision
If ammonothermal method is used to grow GaN, then threading dislocation density can be reduced, but compensation ratio becomes too high
Solution Approach 1:
The patent precisely controls oxygen content in supercritical ammonia and growth temperature (900-1100°C) to regulate dopant incorporation, achieving compensation ratio <4.0 while maintaining low dislocation density through optimized ammonothermal processing parameters
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 consistently produces n-type ammonothermal GaN with a narrowly defined compensation ratio, reduced dislocation density, and enhanced carrier mobility, addressing the limitations of existing methods while maintaining low costs and improving device performance.
Implementation Method 1
polycrystalline group III metal nitride is dissolved and recrystallized in supercritical ammonia
Implementation Method 2
polycrystalline group III metal nitride is dissolved and recrystallized in supercritical ammonia
Data Source
AI summary
A gallium-containing nitride crystals are disclosed, comprising: a top surface having a crystallographic orientation within about 5 degrees of a plane selected from a (0001)+c-plane and a (000-1)−c-plane; a substantially wurtzite structure; n-type electronic properties; an impurity concentration of hydrogen greater than about 5×1017 cm−3, an impurity concentration of oxygen between about 2×1017 cm−3 and about 1×1020 cm−3, an [H]/[O] ratio of at least 0.3; an impurity concentration of at least one of Li, Na, K, Rb, Cs, Ca, F, and Cl greater than about 1×1016 cm−3, a compensation ratio between about 1.0 and about 4.0; an absorbance per unit thickness of at least 0.01 cm−1 at wavenumbers of approximately 3175 cm−1, 3164 cm−1, and 3150 cm−1, and wherein, at wavenumbers between about 3200 cm−1 and about 3400 cm−1 and between about 3075 cm−1 and about 3125 cm−1, said gallium-containing nitride crystal is essentially free of infrared absorption peaks having an absorbance per unit thickness greater than 10% of the absorbance per unit thickness at 3175 cm.