Epitaxial Crystal Substrate via Composition Modulation Layer
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Solution Overview
Problem
Conventional methods for growing epitaxial semiconductor layers with lattice constants different from their substrates result in misfit dislocations and poor crystallinity, especially for long-wavelength semiconductors like InGaAs, due to lattice mismatch, leading to surface defects and high manufacturing costs.
Innovation Solution
A method involving the growth of a composition modulation layer on an off-angle substrate using a step-flow process, where the composition of In x Ga 1-x As is varied stepwise to form a composition modulation layer, allowing the epitaxial growth of InAs y P 1-y with a lattice constant different from InP, thereby reducing lattice mismatch-induced strain and dislocations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a semiconductor material having a lattice constant different from that of the substrate is used in epitaxial growth, then the light wavelength range can be extended to long wavelengths (1.9-2.6 μm), but misfit dislocations are induced in the epitaxial layer when the thickness exceeds the critical thickness, degrading crystallinity
Solution Approach 1:
The epitaxial structure is segmented into multiple functional layers: a composition gradient layer (InAsP with varying composition) at the bottom to gradually adjust lattice constant, a strained InGaAs layer in the middle for long-wavelength emission, and an InAlAs cap layer on top. This segmentation allows each layer to serve its specific function while managing lattice mismatch through the gradient transition layer.
Solution Approach 2:
The composition of the InAsP buffer layer is gradually changed from In-rich (higher lattice constant) at the substrate interface to As-rich (lower lattice constant) toward the InGaAs layer. This continuous parameter change in composition allows the lattice constant to transition smoothly, reducing misfit dislocations and enabling growth of thick InGaAs layers for long-wavelength applications.
2Manufacturing precision
If a composition gradient layer is grown to adjust the lattice constant, then the lattice mismatch is reduced, but the layer thickness becomes relatively thick (4 μm or more), increasing the number of misfit dislocations induced
Solution Approach 1:
The composition gradient is localized to a specific region (the InAsP buffer layer) with optimized thickness and composition profile. Rather than using a thick uniform gradient layer, the gradient is concentrated in a thinner layer with carefully controlled composition variation, reducing overall thickness while maintaining effective lattice constant adjustment.
3Productivity
If MOCVD is used for epitaxial growth, then productivity is improved and thickness/composition control is precise, but the growth rate is lower compared to chloride VPE
Solution Approach 1:
The MOCVD process operates continuously with optimized reaction conditions to maintain steady-state growth. The composition gradient layer is grown in a single continuous process without interruption, ensuring uniform composition control and precise thickness management while maximizing the effective growth rate through continuous material deposition.
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 production of high-quality epitaxial crystal substrates with reduced dislocations and improved crystallinity, allowing for the growth of thick epitaxial layers at a lower cost and in a shorter time, suitable for semiconductor devices requiring long-wavelength applications.
Implementation Method 1
growing a second compound semiconductor on the surface of the substrate by a step-flow process while varying the composition of the second compound semiconductor within the same terrace
Implementation Method 2
growing a second compound semiconductor on the surface of the substrate by a step-flow process
Implementation Method 3
the difference in the lattice constant accumulates strain energy and then induces misfit dislocations in an epitaxial layer with a thickness exceeding a critical thickness
Implementation Method 4
lattice mismatch of more than 0.1% between the first compound semiconductor substrate and the third compound semiconductor epitaxial layer
Data Source
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AI summary
Disclosed is a technology of manufacturing, at low cost, an epitaxial crystal substrate provided with a high-quality and uniform epitaxial layer, said technology being useful in the case of growing the epitaxial layer composed of a semiconductor having a lattice constant different from that of the substrate. The substrate, which is composed of a first compound semiconductor, and which has a step-terrace structure on the surface, is used, and on the surface of the substrate, a composition modulation layer composed of a second compound semiconductor is grown by step-flow, while changing the composition in the same terrace. Then, the epitaxial crystal substrate is manufactured by growing, on the composition modulation layer, the epitaxial layer composed of the third compound semiconductor having the lattice constant different from that of the first compound semiconductor.