Nitride Semiconductor Buffer Stack Lattice Mismatch
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Solution Overview
Problem
The growth of high-quality gallium nitride-based semiconductor devices on substrates like sapphire is hindered by lattice mismatch, leading to defects and cracks, and using special substrates with matching lattice constants is costly.
Innovation Solution
A nitride semiconductor structure with a buffer stack layer composed of repeatedly stacked metal nitride multilayers, each consisting of three thin films with varying aluminum concentrations, is used between the substrate and the nitride semiconductor layer to reduce lattice mismatch, employing a silicon substrate and potentially including an epitaxial layer for improved growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a sapphire substrate is used to grow gallium nitride-based semiconductor, then the substrate is readily available and cost-effective, but lattice mismatch occurs leading to defects and cracks
Solution Approach 1:
A buffer stack layer comprising multiple metal nitride multilayers is introduced as an intermediary between the sapphire substrate and the gallium nitride-based semiconductor layer. This buffer stack layer has a lattice constant that gradually transitions from the substrate to the semiconductor layer, effectively mediating the lattice mismatch and preventing defects and cracks while maintaining the use of cost-effective sapphire substrates
Solution Approach 2:
The buffer stack layer utilizes controlled changes in aluminum concentration across multiple metal nitride thin films to gradually adjust the lattice constant. By varying the aluminum concentration parameter from the substrate interface toward the semiconductor layer, the lattice mismatch is progressively reduced, enabling high-quality gallium nitride growth on sapphire substrates
2Manufacturing precision
If a special substrate with matching lattice constant is used, then lattice quality is improved, but the manufacturing cost becomes too high
Solution Approach 1:
The buffer stack layer acts as a transition intermediary that provides the necessary lattice constant gradient without requiring expensive special substrates. This intermediate structure achieves the lattice matching function at a fraction of the cost of specialized substrates
Solution Approach 2:
By controlling the aluminum concentration parameter in the metal nitride thin films of the buffer stack layer, the lattice constant is gradually adjusted to match between the sapphire substrate and gallium nitride semiconductor, achieving high lattice quality on inexpensive standard substrates
Data Source
AI summary
A nitride semiconductor structure includes a substrate, a nitride semiconductor layer, and a buffer stack layer between the substrate and the nitride semiconductor layer. The buffer stack layer includes a plurality of metal nitride multilayers repeatedly stacked, wherein each of the metal nitride multilayers consists of a first, a second, and a third metal nitride thin films in sequence, or consists of the first, the third, the second, and the third metal nitride thin films in sequence. The aluminum concentration of the first metal nitride thin film is higher than that of the third metal nitride thin film, and the aluminum concentration of the third metal nitride thin film is higher than that of the second metal nitride thin film.