Thick Pseudomorphic Nitride Epitaxial Layers on AlN Substrates
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing semiconductor technologies face challenges in growing thick pseudomorphic layers of AlN, GaN, and InN alloys on AlN substrates without significant strain relaxation, which leads to high defect densities and reduced device performance due to lattice mismatch.
Innovation Solution
The technique involves growing pseudomorphic films of AlN, GaN, and InN alloys on high-quality AlN substrates, exceeding the predicted critical thickness by a factor of at least 5 or 10, using a method that includes forming a buffer layer and graded layers, and optimizing growth conditions such as substrate preparation, temperature, and V-III ratio to maintain low dislocation densities and strain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the thickness of the epitaxial layer is increased to achieve thick pseudomorphic films, then the strain energy in the layer grows and leads to strain relaxation through dislocation motion, surface morphology changes, or cracking
Solution Approach 1:
The patent applies parameter changes by carefully controlling growth conditions including temperature gradients, V-III ratio, and growth rate to enable thick pseudomorphic layers to be maintained without strain relaxation. By adjusting these parameters during epitaxial growth, the system can sustain layers exceeding the predicted critical thickness by factors of 5 or 10 while maintaining low defect densities and preventing dislocation motion or surface morphology degradation
2Reliability
If pseudomorphic layers are grown on low-dislocation substrates, then the epitaxial layer can be grown with very low dislocation densities, but the lattice mismatch causes compressive strain that limits the achievable thickness
Solution Approach 1:
The patent applies preliminary action by preparing the substrate surface with specific treatments and establishing optimal growth conditions before depositing the thick pseudomorphic layer. This includes substrate cleaning, surface preparation, and establishing controlled atmospheric conditions that enable the subsequent growth of extremely thick layers without strain relaxation or defect formation, allowing the system to achieve thicknesses far exceeding conventional limits
3Adaptability or versatility
If the concentration of GaN and InN is increased to achieve desired device applications, then the lattice mismatch with respect to the AlN substrate increases, but pseudomorphic growth can maintain low defect densities
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting growth conditions including temperature, V-III ratio, and precursor flow rates to accommodate varying alloy compositions. This enables the system to grow pseudomorphic layers with high GaN and InN concentrations that would normally exhibit severe lattice mismatch, maintaining low defect densities through real-time parameter optimization during the epitaxial growth process
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 fabrication of high-quality, thick pseudomorphic layers with low defect densities, enabling the production of devices like UV LEDs and laser diodes with improved electrical efficiency and extended lifetime by minimizing strain relaxation and maintaining high carrier mobilities.
Implementation Method 1
When a lattice-mismatched layer is epitaxially grown on a substrate, the initial layer typically grows pseudomorphically—that is, the epitaxial layer will be compressed (experience compressive strain) in the plane of the substrate surface if the intrinsic lattice parameter of the substrate is smaller than that of the epitaxial layer
Implementation Method 2
as the thickness of the epitaxial layer is increased, the strain energy in the epitaxial layer will grow and, typically, the layer will find some way to reduce the strain energy. This may occur by plastic flow through the motion of dislocations, through the creation of surface morphological features which allow strain relaxation, or, particularly when the strain is tensile, through cracking of the film
Data Source
AI summary
Semiconductor structures are fabricated to include strained epitaxial layers exceeding a predicted critical thickness thereof.