GaN Substrate HVPE Growth Impurity Control
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Solution Overview
Problem
Current nitride-based semiconductor substrates face challenges in achieving high transparency and high conductivity simultaneously due to lattice mismatch defects and impurity incorporation during growth processes, particularly in GaN self-standing substrates grown using HVPE, which results in inadequate optical absorption coefficients and reduced crystalline quality.
Innovation Solution
A nitride-based semiconductor substrate with a diameter of 25 mm or more and thickness of 250 micrometers, featuring an optical absorption coefficient of less than 7 cm−1, achieved through the HVPE method using gallium chloride produced by reacting a Ga melt with hydrogen chloride gas for extended periods, forming a thin film with microscopic pores, and controlling the growth to minimize facet formation and impurity concentration, thereby reducing dislocation density and impurity levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If GaN self-standing substrate is grown by conventional HVPE using GaCl3 and NH4Cl, then the substrate can be manufactured, but intermediate products with high moisture absorption property cause incorporation of oxygen and other impurities, reducing transparency
Solution Approach 1:
The patent changes the chemical parameters of the growth system by replacing conventional GaCl3 and NH4Cl with alternative reagents (Ga source and NH3), and adjusts process parameters such as hydrogen partial pressure (5 kPa or more) to prevent impurity incorporation while maintaining manufacturability and achieving high transparency
Solution Approach 2:
The patent creates an inert hydrogen-rich atmosphere during HVPE growth with hydrogen partial pressure of 5 kPa or more, which prevents moisture absorption and impurity incorporation, thereby eliminating the harmful effect on optical transparency while maintaining the manufacturing process
2Reliability
If doping is conducted to secure sufficient conductivity, then electrical conductivity improves, but transparency is reduced
Solution Approach 1:
The patent optimizes doping parameters and concentration levels, achieving sufficient electrical conductivity (resistivity of 0.02 ohm·cm or less) while controlling dopant distribution and concentration to minimize optical absorption, thereby resolving the trade-off between conductivity and transparency
3Ease of manufacture
If lattice mismatch between sapphire substrate and GaN is not perfectly eliminated, then GaN can be grown on sapphire substrate, but the grown GaN has a number of defects
Solution Approach 1:
The patent extracts the GaN crystal layer from the sapphire substrate to create a self-standing GaN substrate, eliminating the lattice mismatch problem entirely. This allows high-quality GaN with low defect density to be achieved while maintaining the manufacturing advantage of using sapphire as a growth substrate
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 approach results in a substrate with high transparency, low optical absorption, and sufficient conductivity, with electrical resistivity of 0.02 ohm·cm or less and impurity concentrations below 1×10^17 cm−3, enhancing the efficiency of light-emitting devices by minimizing defects and impurities.
Implementation Method 1
gallium chloride produced by reacting a Ga melt with hydrogen chloride gas
Implementation Method 2
epitaxially thereon growing a GaN single crystal layer by HVPE
Data Source
AI summary
A nitride-based semiconductor substrate having a diameter of 25 mm or more, a thickness of 250 micrometers or more, and an optical absorption coefficient of less than 7 cm−1 to light with a wavelength of 380 nm or more. The nitride-based semiconductor substrate is made by the HVPE method that uses gallium chloride obtained by reacting a Ga melt with a hydrogen chloride gas. The Ga melt is contacted with the hydrogen chloride gas for one minute or more to produce the gallium chloride.