Vertically Oriented Growth of GaN Nanorods on Si Using Graphene as an Atomically Thin Buffer Layer

Area of Science:

• Materials Science
• Nanotechnology
• Semiconductor Physics

Background:

• Monolithic integration of wurtzite gallium nitride (GaN) on silicon (Si) is challenging due to lattice and thermal mismatch, and meltback etching.
• Existing methods struggle to achieve high-quality GaN growth directly on Si.

Purpose of the Study:

• To investigate the use of single-layer graphene as a buffer layer for GaN nanorod growth on Si.
• To demonstrate the feasibility of growing vertically aligned GaN nanorods with high crystal and optical quality on graphene/Si substrates.
• To assess the electrical properties of the synthesized GaN nanostructures.

Main Methods:

• Metal-organic vapor phase epitaxy (MOVPE) for GaN nanorod growth on graphene-covered Si(111) and Si(100).
• Characterization using scanning transmission electron microscopy (STEM), micro-Raman spectroscopy, and cathodoluminescence (CL).
• Finite-difference time-domain (FDTD) simulations to support optical measurements.
• Current-voltage (I-V) measurements to evaluate vertical conduction.

Main Results:

• Successful growth of c-axis-oriented, vertically aligned GaN nanorods on graphene/Si using AlGaN nucleation islands.
• High crystal and optical quality of GaN nanorods confirmed by STEM, Raman, and CL.
• Demonstrated high vertical electrical conductivity of GaN nanorods through the Si substrate.
• Achieved similar nanostructure morphology on both Si(111) and Si(100) substrates.

Conclusions:

• Single-layer graphene acts as an effective atomically thin buffer layer for GaN nanorod epitaxy on silicon.
• This approach overcomes significant integration hurdles, enabling high-quality GaN growth on diverse substrates.
• The findings facilitate novel designs for GaN-based heterojunction devices and advanced electronic applications.