GaN on Silicon Buffer Layer for Breakdown Voltage
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Solution Overview
Problem
The growth of GaN films on silicon substrates is challenging due to lattice constant and thermal expansion coefficient mismatches, leading to interfacial stresses and defects, and unintentional doping with impurities like silicon and oxygen results in detrimental electrical properties for high electron mobility transistors and heterojunction bipolar transistors.
Innovation Solution
A method involving a low-temperature nucleation layer of aluminum nitride, followed by a graded buffer layer with p-type dopants and an ungraded buffer layer to achieve an intrinsically balanced conductivity state, reducing interfacial stress and increasing breakdown voltage, while compensating for unintentional n-type doping from silicon and oxygen impurities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If GaN films are grown on silicon substrates, then cost is reduced and substrate availability is improved, but lattice mismatch and thermal expansion differences cause interfacial stress and defects
Solution Approach 1:
A silicon nitride buffer layer is introduced as an intermediary between the silicon substrate and the GaN film. This buffer layer mediates the lattice mismatch and thermal expansion differences, reducing interfacial stress and preventing defect propagation into the GaN film while maintaining the cost advantages of silicon substrates
Solution Approach 2:
The patent modifies the buffer layer composition and thickness parameters to optimize stress compensation. By adjusting the silicon nitride buffer layer properties, the system achieves better lattice matching and thermal compatibility, improving film quality without changing the silicon substrate itself
2Ease of manufacture
If unintentional doping from silicon and oxygen impurities occurs, then film formation is simplified, but electrical properties are degraded
Solution Approach 1:
The silicon nitride buffer layer acts as a protective intermediary that filters and controls impurity diffusion. It allows simplified film formation processes while preventing harmful silicon and oxygen impurities from reaching the GaN layer, thus maintaining good electrical properties
Solution Approach 2:
The patent converts the potentially harmful effect of silicon and oxygen impurities into a beneficial outcome. The buffer layer is designed to utilize controlled impurity incorporation to create a graded transition region that actually improves interface quality while blocking harmful impurities from the GaN film
3Reliability
If thicker GaN films are grown to increase breakdown voltage, then device performance is improved, but defect density increases due to interfacial stress
Solution Approach 1:
The silicon nitride buffer layer serves as a stress-absorbing intermediary that enables growth of thicker GaN films. It compensates for interfacial stress throughout the film thickness, allowing breakdown voltage to increase with film thickness without proportional increase in defect density
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 allows for the growth of thicker GaN films with reduced defects and increased breakdown voltage, enhancing the electrical properties and reliability of high electron mobility transistors and other III-V compound semiconductor devices.
Implementation Method 1
a nucleation layer of aluminum nitride is grown at a low temperature on the substrate
Implementation Method 2
a graded buffer layer with p-type dopants and an ungraded buffer layer to achieve an intrinsically balanced conductivity state, reducing interfacial stress and increasing breakdown voltage, while compensating for unintentional n-type doping from silicon and oxygen impurities
Data Source
AI summary
A circuit structure includes a substrate, a nucleation layer of undoped aluminum nitride, a graded buffer layer comprising aluminum, gallium, nitrogen, one of silicon and oxygen, and a p-type conductivity dopant, a ungraded buffer layer comprising gallium, nitrogen, one of silicon and oxygen, and a p-type conductivity dopant without aluminum, and a bulk layer of undoped gallium nitride over the ungraded buffer layer. The various dopants in the graded buffer layer and the ungraded buffer layer increases resistivity and results in layers having an intrinsically balanced conductivity.