Bulk Crystalline 4H Silicon via Si24 Allotropic Transition
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Solution Overview
Problem
The production of high-quality bulk 4H phase silicon has been elusive due to previous methods yielding nanocrystalline materials with disordered regions, making structural identification ambiguous and preventing characterization of its optical band gap.
Innovation Solution
Heating Si24, another silicon allotrope, above 300°C at atmospheric pressure or 800°C under high pressure near 9 GPa results in highly oriented 4H silicon microcrystals with no disordered material, enabling unambiguous Raman spectra and X-ray diffraction patterns, and allowing for the first characterization of the optical band gap.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If previous methods (heating BC8 silicon) are used to produce 4H silicon, then 4H phase silicon can be formed, but the product is nanocrystalline and coexists with amorphous/disordered material, making structural identification ambiguous
Solution Approach 1:
The patent changes the precursor material parameter from BC8 silicon to Si24 allotrope, and adjusts temperature parameters (heating to 800-1000°C) to achieve bulk crystalline 4H silicon with high structural order, eliminating the nanocrystalline and amorphous issues of previous methods
Solution Approach 2:
The patent extracts and eliminates the disordered and amorphous components from the product by using a refined synthesis pathway from Si24, resulting in high-purity bulk crystalline 4H silicon that enables clear structural identification through XRD and Raman spectroscopy
2Volume of stationary object
If previous methods are used to produce 4H silicon, then the material can be synthesized, but bulk crystalline form cannot be achieved, only nanocrystalline forms with disordered regions
Solution Approach 1:
The patent changes the synthesis parameters including using Si24 as precursor and heating to 800-1000°C, which enables the formation of bulk crystalline 4H silicon with high structural order, overcoming the nanocrystalline limitation of previous BC8-based methods
Solution Approach 2:
The patent uses Si24 allotrope as a pre-prepared precursor with suitable structural characteristics that facilitates the formation of bulk crystalline 4H silicon during heating, avoiding the disordered intermediate states that occur in BC8-based synthesis
3Measurement precision
If previous methods are used, then 4H silicon can be produced, but optical band gap characterization cannot be performed due to disordered material presence
Solution Approach 1:
The patent changes the synthesis approach to use Si24 precursor and controlled heating (800-1000°C) to produce high-purity bulk crystalline 4H silicon, enabling clear optical band gap characterization at 1.2 eV that was impossible with disordered nanocrystalline materials from previous methods
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 produces high-quality, crystalline 4H silicon with an indirect band gap near 1.2 eV, suitable for semiconductor applications, and provides a novel route to access bulk crystalline 4H silicon, overcoming previous limitations of nanocrystalline and disordered materials.
Implementation Method 1
Bulk crystalline 4h-silicon through a metastable allotropic transition
Implementation Method 2
The synthesis of bulk, highly oriented, crystalline 4H hexagonal silicon (4H—Si) occurs through a metastable phase transformation upon heating the single-crystalline Si24 allotrope
Implementation Method 3
4H—Si forms when Si24 is heated above 300° C. at atmospheric pressure, and also when heated to 800° C. at high pressure near 9 GPa
Data Source
AI summary
A novel bulk form of 4H-Si, a crystalline allotrope of silicon and a novel method of manufacture. The novel material consists of highly oriented microcrystals of silicon in the 4H structure with no disordered material. The 4H-Si is derived from heating a second novel material Si24 under proper conditions. The allotrope of silicon is produced as bulk, microcrystalline agglomerates.