Planar Semipolar GaN Growth on Patterned Sapphire
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Solution Overview
Problem
Current methods fail to successfully form microfabrication-grade, planar semipolar gallium nitride (GaN) layers on sapphire substrates, which are essential for high-efficiency light-emitting diodes and transistors due to challenges in crystal orientation and surface roughness.
Innovation Solution
A method involving patterned sapphire substrates with a surface-grating structure and a masking process to control crystal growth, followed by epitaxial growth using a nitrogen carrier gas to achieve a smooth, planar semipolar GaN layer, which is then planarized and regrown to ensure a flat surface for device fabrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional epitaxial growth methods are used on sapphire substrates, then crystal growth can be achieved, but the surface roughness and crystal orientation are insufficient for microfabrication-grade devices
Solution Approach 1:
The sapphire substrate is patterned with an array of trenches that divide the surface into discrete crystal-growth surfaces. This segmentation allows selective epitaxial growth on specific facets while preventing growth on others, enabling precise control over crystal orientation and surface planarity for microfabrication-grade devices
Solution Approach 2:
Different regions of the substrate are given different properties through the trench pattern. The crystal-growth surfaces have exposed c-plane or inclined c-plane orientations optimized for epitaxial growth, while masked surfaces prevent nucleation. This local differentiation achieves the required surface planarity and crystal orientation quality
2Manufacturing precision
If hydrogen carrier gas is used during epitaxial growth, then growth can proceed, but the resulting surface is not sufficiently flat for integrated device fabrication
Solution Approach 1:
The carrier gas is changed from hydrogen to nitrogen during the epitaxial growth process. This parameter change fundamentally alters the growth dynamics, enabling the formation of atomically smooth, planar surfaces with RMS roughness below 5 nm over 15 μm×15 μm areas, which is essential for integrated device fabrication
3Reliability
If bulk III-nitride substrates are used, then high-purity crystalline material can be obtained, but the cost and difficulty of growth increase significantly
Solution Approach 1:
A patterned sapphire substrate serves as an intermediary platform that enables epitaxial growth of high-purity III-nitride layers without requiring expensive bulk III-nitride substrates. The patterned structure with trenches and masked surfaces guides the epitaxial growth process to produce microfabrication-grade material at lower cost
Solution Approach 2:
The sapphire substrate with its patterned trench structure acts as a disposable template that facilitates the growth of high-quality III-nitride layers. The substrate itself does not need to be high-cost bulk III-nitride material, allowing cost-effective production while achieving the required material purity
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 enables the formation of high-quality, planar semipolar GaN layers with reduced defects and surface roughness, suitable for integrated circuit devices, overcoming previous limitations in crystal orientation and surface quality.
Implementation Method 1
semipolar III-nitride semiconductor may be grown from these crystal-growth surfaces
Implementation Method 2
A masking process may be carried out prior to semiconductor growth to prevent nucleation and growth at other surfaces of the patterned sapphire substrate
Implementation Method 3
Growth of the semipolar material may be continued, so that the material coalesces and forms a continuous III-nitride layer
Implementation Method 4
During regrowth, a nitrogen carrier gas, instead of a hydrogen carrier gas, may be used to provide a flat, semipolar, atomically-smooth process surface
Data Source
AI summary
Methods and structures for forming flat, continuous, planar, epitaxial layers of semipolar III-nitride materials on patterned sapphire substrates are described. Semipolar GaN may be grown from inclined c-plane facets on a patterned sapphire substrate, and coalesced to form a continuous layer of semipolar III-nitride semiconductor over the sapphire substrate. Planarization of the layer is followed by crystal regrowth using a nitrogen carrier gas to produce a flat, microfabrication-grade, process surface of semipolar III-nitride semiconductor across the substrate. Quality multiple quantum wells can be fabricated in the regrown semipolar material.