Carbon-Doped GaN Substrate Structure for Low-Loss RF Operation
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Solution Overview
Problem
Existing nitride semiconductor substrates face challenges in achieving high-frequency characteristics due to stress-induced cracking, substrate warping, and high-frequency signal loss, particularly when forming thick GaN films, which are necessary for advanced communication technologies like 5G.
Innovation Solution
A nitride semiconductor substrate is developed with a composite structure including a single-crystal silicon layer and a GaN layer doped with specific concentrations of carbon and/or iron, ranging from 1×10^19 to 5×10^20 atoms/cm^3, to enhance resistivity and reduce high-frequency loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick GaN film is formed on Si or SiC substrate, then the breakdown voltage and high-frequency characteristics are improved, but stress-induced cracking occurs due to thermal expansion mismatch
Solution Approach 1:
The patent changes the material parameter of the substrate from conventional Si or SiC to a composite substrate containing a (0001)-oriented GaN layer, which has matched thermal expansion characteristics with the GaN film. This parameter change eliminates thermal stress during temperature changes, preventing cracking while enabling thick film formation for high breakdown voltage devices.
Solution Approach 2:
The patent employs a composite substrate structure consisting of a (0001)-oriented GaN layer formed on a SiC substrate. This composite material approach combines the benefits of SiC (mechanical strength, thermal conductivity) with oriented GaN (thermal expansion match), achieving both crack resistance and high breakdown voltage capability.
2Reliability
If a thick GaN film is formed to improve high-frequency characteristics, then signal transmission quality is enhanced, but substrate warping occurs during epitaxial growth and cooling
Solution Approach 1:
The patent changes the substrate material parameter to a composite with (0001)-oriented GaN layer that has matched thermal expansion characteristics. This eliminates differential expansion during heating and cooling cycles, preventing warping while enabling formation of thick GaN films necessary for high-frequency device operation.
3Productivity
If conventional substrates are used for GaN film formation, then mass production is possible, but high-frequency signal loss occurs due to insufficient resistivity
Solution Approach 1:
The patent changes the substrate composition to include a (0001)-oriented GaN layer on SiC, which provides inherently high resistivity. This parameter change reduces high-frequency signal loss while maintaining compatibility with mass production processes through MOCVD epitaxial growth.
Solution Approach 2:
The composite substrate structure combines SiC substrate (mechanical support, thermal management) with (0001)-oriented GaN layer (high resistivity, thermal expansion match). This composite material provides both low signal loss and mass production capability through established epitaxial techniques.
4Ease of manufacture
If Si or SiC substrates are used for large-diameter GaN devices, then cost and diameter enlargement are achieved, but thermal expansion mismatch causes stress and cracking
Solution Approach 1:
The patent changes the substrate material parameter from conventional Si/SiC to a composite with (0001)-oriented GaN layer. This parameter change maintains large-diameter availability and reasonable cost while eliminating thermal expansion mismatch, enabling crack-free large-area GaN devices for power electronics and RF applications.
Solution Approach 2:
The composite substrate combines SiC (mechanical strength, large diameter availability) with (0001)-oriented GaN layer (thermal expansion match). This composite material achieves both ease of manufacture for large devices and crack resistance through thermal compatibility.
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 substrate achieves improved high-frequency characteristics by making the GaN layer highly resistive, reducing signal transmission and loss, and allowing for thicker GaN film formation without cracking or warping, thus supporting advanced communication technologies.
Implementation Method 1
the GaN layer is doped with at least 1×10^19 atoms/cm^3 or more and less than 5×10^20 atoms/cm^3 of carbon and/or 5×10^18 atoms/cm^3 or more and less than 5×10^20 atoms/cm^3 of iron
Implementation Method 2
these substrates have different coefficients of thermal expansion with GaN. Thus, stress applied due to a cooling process after an epitaxial film-forming is likely to generate a crack
Data Source
AI summary
The present invention provides a nitride semiconductor substrate including a substrate for film formation including a composite substrate having a plurality of layers bonded together and a single-crystal silicon layer formed on the composite substrate and a nitride semiconductor thin film formed on the substrate for film formation. The nitride semiconductor thin film includes a GaN layer, and the GaN layer is doped with at least 1×1019 atoms/cm3 or more and less than 5×1020 atoms/cm3 of carbon and/or 5×1018 atoms/cm3 or more and less than 5×1020 atoms/cm3 of iron. Thereby, the nitride semiconductor substrate with an improved high-frequency characteristic and a method of producing this substrate can be provided.