GaN Crystal Substrate Doping for Low Voltage and High Optical Output
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Solution Overview
Problem
GaN crystal substrates used in light-emitting devices have high light absorption coefficients, leading to reduced optical output, and sapphire substrates cannot form electrodes on their back surfaces due to insulating properties, increasing driving voltage.
Innovation Solution
A GaN crystal substrate with a diameter of at least 20 mm and thickness of 70 μm to 450 μm, featuring a light absorption coefficient of 7 cm−1 to 68 cm−1 for wavelengths between 375 nm and 500 nm, and doped with elements like oxygen, carbon, or silicon, fabricated using a method involving GaAs substrates and HVPE growth to reduce absorption and enhance conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a GaN crystal substrate is used as the substrate for a light-emitting device, then it is possible to form the electrode on the back surface of the GaN crystal substrate having a large cross section and reduce the driving voltage, but the light emitted from the light-emitting layer would be absorbed by the GaN crystal substrate in a greater amount, degrading the optical output
Solution Approach 1:
The invention changes the physical and chemical parameters of the GaN crystal substrate, specifically controlling the carrier concentration to be between 5×10^17 cm^-3 and 2×10^19 cm^-3, and incorporating dopants (O, C, S, or Si) at controlled concentrations. These parameter changes reduce the light absorption coefficient to 7-68 cm^-1 while maintaining electrical conductivity, thereby resolving the contradiction between reduced driving voltage and maintained optical output.
Solution Approach 2:
The invention creates a composite structure by incorporating multiple dopant elements (O, C, S, Si) into the GaN crystal lattice at controlled concentrations. This composite doping approach allows simultaneous optimization of electrical and optical properties, achieving both low driving voltage and high optical output by balancing carrier concentration with light absorption characteristics.
2Loss of energy
If a sapphire substrate is used as the substrate for a light-emitting device, then the light absorption is reduced, but it is not possible to form an electrode on the back surface of the sapphire substrate due to high insulating property, increasing the driving voltage
Solution Approach 1:
The invention transforms the sapphire substrate's insulating properties by using GaN crystal substrate with controlled carrier concentration (5×10^17 cm^-3 to 2×10^19 cm^-3) and dopant incorporation. This parameter change enables electrical conductivity sufficient for back-surface electrode formation while maintaining optical transparency, thus resolving the contradiction between optical output and driving voltage.
3Ease of operation
If the carrier concentration of the GaN crystal substrate is increased to reduce driving voltage, then the electrical conductivity improves, but the light absorption coefficient increases, reducing optical output
Solution Approach 1:
The invention optimizes the carrier concentration parameter to a specific range (5×10^17 cm^-3 to 2×10^19 cm^-3) and combines it with controlled dopant incorporation (O, C, S, or Si at 10^18 to 10^20 atoms/cm³). This precise parameter control achieves the optimal balance between electrical conductivity for low driving voltage and light absorption coefficient for high optical output.
Solution Approach 2:
The invention uses composite doping with multiple elements (O, C, S, Si) at controlled concentrations to achieve simultaneous optimization of electrical and optical properties. The composite dopant structure allows independent control of carrier concentration and light absorption, resolving the contradiction between conductivity and optical transparency.
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 solution results in a GaN crystal substrate with reduced light absorption and lower driving voltage for light-emitting devices, while maintaining mechanical strength and optical output, achieving improved performance in light-emitting devices.
Implementation Method 1
the GaN crystal substrate has a light absorption coefficient of not less than 7 cm−1 and not more than 68 cm−1 for light in a wavelength range of not less than 375 nm and not more than 500 nm
Implementation Method 2
epitaxially growing a GaN crystal layer on the GaN buffer layers by HVPE
Data Source
AI summary
A GaN crystal substrate is provided, which has a diameter of not less than 20 mm and a thickness of not less than 70 μm and not more than 450 μm, and has a light absorption coefficient of not less than 7 cm−1 and not more than 68 cm−1 for light in the wavelength range of not less than 375 nm and not more than 500 nm. A fabricating method of the GaN crystal substrate, and a light-emitting device fabricated using the GaN crystal substrate are also provided.