Bulk Crystalline 4H-Silicon through a Metastable Allotropic Transition.

Area of Science:

• Materials Science
• Solid-State Physics
• Crystallography

Background:

• Silicon (Si) is a foundational material in semiconductor technology.
• Exploring novel silicon allotropes and crystalline phases is crucial for advancing electronic and optoelectronic devices.
• Previous methods for synthesizing 4H-Si often resulted in nanocrystalline or disordered materials.

Purpose of the Study:

• To report the synthesis of bulk, highly oriented, crystalline 4H hexagonal silicon (4H-Si).
• To investigate the structural relationship between 4H-Si and the Si_{24} allotrope.
• To characterize the electronic properties of the synthesized 4H-Si.

Main Methods:

• Synthesis of 4H-Si via metastable phase transformation of single-crystalline Si_{24} upon heating.
• Analysis of crystallite orientation relationships using diffraction techniques.
• Optical absorption spectroscopy to determine the band gap.
• First principles calculations for theoretical validation.

Main Results:

• Successfully synthesized bulk, highly oriented, crystalline 4H-Si.
• Observed a distinct orientation relationship between 4H-Si and Si_{24} crystals.
• Measured an indirect band gap of approximately 1.2 eV for 4H-Si, consistent with theoretical predictions.
• Demonstrated a novel metastable transition pathway.

Conclusions:

• The metastable phase transformation of Si_{24} provides a viable route to bulk crystalline 4H-Si.
• The identified structural relationship offers insights into silicon allotrope transformations.
• The synthesized 4H-Si with its determined band gap shows potential for future electronic applications.