Nitride Semiconductor Epitaxial Stack Structure for Silicon Substrates
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Solution Overview
Problem
The challenge lies in forming high-quality nitride semiconductor epitaxial stack structures on silicon substrates, as existing methods often result in high epitaxial defect densities and surface cracks due to lattice mismatch, affecting the performance of power devices and Schottky devices.
Innovation Solution
A nitride semiconductor epitaxial stack structure is developed, featuring a silicon substrate with an AlN nucleation layer, a buffer structure comprising alternating superlattice and GaN-based layers, and a channel and barrier layer configuration, where the Al composition ratio is gradually adjusted to reduce stress and defects, resulting in a thicker GaN-based layer stack exceeding 2 micrometers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a silicon substrate is used for growing nitride semiconductor epitaxial stack structure, then the cost is reduced and manufacturing is easier, but the lattice mismatch causes high epitaxial defect density and surface cracks
Solution Approach 1:
The patent divides the buffer structure into multiple segments: AlN nucleation layer, first superlattice buffer layer (AlGaN/GaN), second superlattice buffer layer (AlGaN/GaN), and GaN cap layer. Each layer serves as an intermediate step to gradually bridge the lattice mismatch between silicon substrate and nitride semiconductor, reducing defect density while maintaining manufacturing feasibility on silicon substrates
Solution Approach 2:
The patent changes the compositional parameters of the buffer layers by using AlGaN alloys with varying aluminum content in the superlattice structures. This gradual composition transition from high-Al content (AlN) to low-Al content (GaN) allows progressive lattice constant adjustment, reducing the sudden stress that causes cracks while maintaining the advantage of using inexpensive silicon substrates
2Reliability
If the Al composition ratio is gradually adjusted in the buffer structure, then the stress and epitaxial defects are reduced, but the device structure becomes more complex
Solution Approach 1:
The patent applies local quality by creating different buffer layer configurations in different regions of the epitaxial stack. The first and second superlattice buffer layers have different Al composition ratios and thicknesses, allowing localized stress management and defect reduction in specific areas where they are most needed, while keeping the overall structure manageable
Solution Approach 2:
The patent uses composite material structures by combining AlN, AlGaN with different compositions, and GaN in a layered superlattice configuration. This composite approach allows the buffer structure to simultaneously provide lattice matching, stress relief, and defect filtering functions, improving device reliability without requiring excessive individual layers
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 significantly reduces epitaxial defect density and surface cracks, enhancing the quality and performance of nitride semiconductor power devices by improving the epitaxial layer's flatness and reducing stress, leading to better operational reliability and breakdown voltage resistance.
Implementation Method 1
forming an AlN nucleation layer on a silicon substrate by metal-organic chemical vapor deposition (MOCVD) method, and further forming a superlattice stack layer including alternately multiple AlN superlattice layers of a thickness of 18 nm each and GaN superlattice layers of a thickness of 5 nm each by the same MOCVD method
Implementation Method 2
because of the differences of lattice constant and expansion coefficient between the substrate material and the nitride semiconductor material, epitaxial defect is easily occurred within an epitaxial layer when forming the epitaxial layer on the substrate
Implementation Method 3
the Al composition ratio of the AlN nucleation layer≥the first average Al composition ratio of the first superlattice epitaxial structure>the first Al composition ratio of the first GaN based layer>the second average Al composition ratio of the second superlattice epitaxial structure
Data Source
AI summary
A nitride semiconductor epitaxial stack structure including: a silicon substrate; an AlN nucleation layer disposed on the silicon substrate; a buffer structure disposed on the aluminum-including nucleation layer and sequentially including a first superlattice epitaxial structure, a first GaN-based layer disposed on the first superlattice epitaxial structure, and a second superlattice epitaxial structure disposed on the first GaN based layer; a channel layer disposed on the buffer structure; and a barrier layer disposed on the channel layer; wherein the first superlattice epitaxial structure includes a first average Al composition ratio, the first GaN-based layer includes a first Al composition ratio, the_second superlattice epitaxial structure includes a second average Al composition ratio; wherein an Al composition ratio of the AlN nucleation layer≥the first average Al composition ratio of the first superlattice epitaxial structure>the first Al composition ratio of the first GaN based layer>the second average Al composition ratio of the second superlattice epitaxial structure.