Crystalline Germanium Layer on Silicon Substrate
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Solution Overview
Problem
The large lattice mismatch between Germanium (Ge) and Silicon (Si) substrates leads to high surface roughness and threading dislocations in Ge epilayers, making it difficult to achieve high-quality crystalline Ge layers for CMOS and photovoltaic applications.
Innovation Solution
A method involving cleaning the Si substrate, depositing an amorphous Ge layer while exposing it to a hydrogen source or non-reactive gas, and subsequent annealing to crystallize the layer, which reduces surface mobility and promotes single-crystalline growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional epitaxial growth methods are used to form Ge layers on Si substrates, then Ge layers can be deposited, but high surface roughness and threading dislocations occur due to large lattice mismatch
Solution Approach 1:
The patent employs solid-phase epitaxial growth where an amorphous Ge layer is transformed into a crystalline structure through thermal annealing. This phase transition approach allows the Ge layer to recrystallize with reduced defects and improved surface quality, overcoming the lattice mismatch problems that plague conventional direct epitaxial growth methods
Solution Approach 2:
The patent applies preliminary surface treatment including cleaning the Si substrate and forming a specific surface structure before Ge deposition. This preliminary action prepares the substrate surface to reduce nucleation sites for dislocations and control the initial growth morphology, thereby reducing surface roughness and threading dislocations in the final Ge layer
2Manufacturing precision
If conventional epitaxial growth methods are used to form Ge layers on Si substrates, then Ge layers can be deposited, but high densities of threading dislocations occur due to large lattice mismatch
Solution Approach 1:
The patent employs solid-phase epitaxial growth where an amorphous Ge layer is transformed into a crystalline structure through thermal annealing. This phase transition approach allows the Ge layer to recrystallize with reduced defects and improved surface quality, overcoming the lattice mismatch problems that plague conventional direct epitaxial growth methods
Solution Approach 2:
The patent introduces an amorphous Ge layer as an intermediary state between the Si substrate and the final crystalline Ge layer. This intermediary amorphous phase acts as a buffer that accommodates the lattice mismatch, allowing subsequent epitaxial crystallization to proceed with fewer threading dislocations
3Manufacturing precision
If high temperature annealing is used to crystallize Ge layers, then crystalline structure is achieved, but Ge mixes with Si and SiGe is formed
Solution Approach 1:
The patent employs solid-phase epitaxial growth where an amorphous Ge layer is transformed into a crystalline structure through thermal annealing. This phase transition approach allows the Ge layer to recrystallize with reduced defects and improved surface quality, overcoming the lattice mismatch problems that plague conventional direct epitaxial growth methods
Solution Approach 2:
The patent optimizes the annealing temperature and time parameters to achieve crystallization of the amorphous Ge layer while staying below the threshold temperature for significant Ge-Si interdiffusion. By carefully controlling these parameters, the method achieves crystalline Ge with maintained compositional purity and avoided SiGe alloy formation
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 method results in high-quality, monocrystalline Ge layers with improved crystal quality and surface smoothness, reducing surface roughness and threading dislocations, suitable for CMOS and photovoltaic cell fabrication.
Implementation Method 1
exposing it to a hydrogen source or non-reactive gas, and subsequent annealing to crystallize the layer, which reduces surface mobility and promotes single-crystalline growth
Implementation Method 2
crystallising the amorphous germanium layer by annealing the base substrate
Implementation Method 3
subsequent annealing to crystallize the layer, which reduces surface mobility and promotes single-crystalline growth
Data Source
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AI summary
The present invention provides a method for providing a crystalline germanium layer on a crystalline base substrate having a crystalline surface. The method comprises cleaning the base substrate for removing contaminants and/or native oxides from the surface, providing an amorphous germanium layer on the surface of the base substrate while exposing to the base substrate to a hydrogen source such as e.g. a hydrogen plasma, a H2 flux or hydrogen originating from dissociation of GeH4 and/or to a non-reactive gas source such as N2, He, Ne, Ar, Kr, Xe, Rn or mixtures thereof, and crystallising the amorphous germanium layer by annealing the base substrate so as to provide a crystalline germanium layer. The present invention also provides a method for the production of a photovoltaic cell or a photo-electrolysis cell or for forming a CMOS device by using the method according to embodiments of the invention and a substrate comprising a crystalline germanium layer formed by a method according to embodiments of the invention.