Graded GeSn Template for III-V Solar Cells on Silicon
Solution Overview
Problem
The deposition of III-V semiconductor materials on GeSn on silicon wafers faces challenges due to poor quality GeSn, leading to limited layer thickness, cracking, stress fractures, and poor interfaces, resulting in reduced solar cell efficiency and increased costs.
Innovation Solution
A method involving the epitaxial growth of a graded single crystal GeSn layer on a silicon substrate, with a thickness of 3 μm to 5 μm, where Sn is graded through the layer to improve the interface with III-V solar collection materials, allowing for higher crystalline quality and reduced cracking, and subsequent growth of III-V materials on this template.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If GeSn is grown on silicon substrates with constant mole fraction of Sn, then the absorption spectrum is extended into lower energy light, but the layer thickness is limited due to cracking and stress fractures
Solution Approach 1:
The patent applies parameter changes by implementing a graded Sn composition profile instead of constant mole fraction. The Sn content is gradually increased from 0% at the silicon interface to a maximum value (e.g., 10-20%) at the top surface, which reduces lattice mismatch and minimizes stress accumulation, allowing thicker layers to be grown without cracking while maintaining extended absorption spectrum
Solution Approach 2:
The patent applies local quality by creating spatial variation in Sn concentration within the GeSn layer. Different regions of the layer have different Sn compositions - lower Sn content near the silicon substrate and higher Sn content at the surface - which optimizes both the mechanical stability (preventing cracks) and the optical absorption properties (extending to lower energy light) in their respective locations
2Use of energy by moving object
If GeSn layers are grown with higher Sn content to extend absorption spectrum, then solar energy absorption is improved, but cracking and stress fractures increase
Solution Approach 1:
The patent gradually changes the Sn composition parameter through the layer thickness, transitioning from low Sn content at the silicon interface to higher Sn content at the surface. This gradual parameter change reduces the lattice mismatch between adjacent layers, minimizing stress accumulation and preventing cracking while still achieving high Sn content for extended absorption spectrum
Solution Approach 2:
The patent performs preliminary action by first growing a thin buffer layer of Ge or low-Sn GeSn on the silicon substrate before growing the higher-Sn GeSn layer. This preliminary layer acts as a transition that reduces the initial lattice mismatch and stress, preventing cracking from the outset while allowing the subsequent high-Sn layer to achieve superior absorption properties
3Ease of manufacture
If GeSn is grown directly on silicon substrates, then cost is reduced compared to germanium wafers, but poor quality GeSn results in poor interfaces and reduced solar cell efficiency
Solution Approach 1:
The patent applies local quality by creating a graded composition profile where the Sn content varies continuously from 0% at the silicon interface to a maximum value at the surface. This local variation in composition optimizes the interface region by matching lattice constants, ensuring high crystalline quality and excellent interfaces while maintaining the cost advantage of growing on silicon substrates
Solution Approach 2:
The patent introduces an intermediary graded GeSn layer between the silicon substrate and the final high-Sn GeSn layer or III-V materials. This intermediary layer with intermediate composition acts as a buffer that reduces lattice mismatch and dislocation density, ensuring high-quality interfaces while enabling the growth of thick, high-Sn layers for extended absorption spectrum
4Reliability
If germanium wafers are used as substrates, then desirable semiconductor properties are achieved, but the cost increases to approximately 50% of total device cost
Solution Approach 1:
The patent creates a synthetic GeSn layer with graded composition that copies the desirable semiconductor properties of germanium while being grown on inexpensive silicon substrates. The graded GeSn layer replicates the lattice structure and crystalline quality of high-quality germanium wafers, providing similar semiconductor performance at a fraction of the cost
Solution Approach 2:
The patent changes the composition parameter of the GeSn layer, gradually increasing Sn content from 0% to a maximum value (e.g., 10-20%). This parameter change allows the layer to maintain excellent crystalline quality and semiconductor properties similar to germanium while being grown on low-cost silicon substrates, achieving both reliability and ease of manufacture
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 enhances the crystalline quality of GeSn and improves interfaces between materials, resulting in higher efficiency, cost-effectiveness, and easier production of solar cells with increased solar energy absorption across a broader spectrum.
Implementation Method 1
epitaxially growing a single crystal GeSn layer on the silicon substrate using a grading profile to grade Sn through the layer
Implementation Method 2
using a grading profile to grade Sn through the layer
Data Source
AI summary
A method of depositing III-V solar collection materials on a GeSn template on a silicon substrate including the steps of providing a crystalline silicon substrate and epitaxially growing a single crystal GeSn layer on the silicon substrate using a grading profile to grade Sn through the layer. The single crystal GeSn layer has a thickness in a range of approximately 3 μm to approximately 5 μm. A layer of III-V solar collection material is epitaxially grown on the graded single crystal GeSn layer. The graded single crystal GeSn layer includes Sn up to an interface with the layer of III-V solar collection material.