Optimization for growth condition of ultrathin hexagonal boron nitride on dielectric substrates via LPCVD

TL;DR

This paper presents optimized LPCVD growth conditions for directly synthesizing high-quality ultrathin hexagonal boron nitride films on dielectric substrates like quartz, eliminating transfer-related damage for optoelectronic applications.

Contribution

It introduces a method to grow high-quality h-BN directly on dielectric substrates using LPCVD, with specific optimized parameters for improved device integration.

Findings

Optimal growth at 1050°C for 60 min

Achieved high-quality ultrathin h-BN films on quartz

Eliminated transfer-related damage in fabrication

Abstract

Hexagonal Boron Nitride (h-BN) is a highly intriguing candidate for heterostructure optoelectronic applications, such as Deep Ultraviolet photodetectors, UV sensing and communication systems and solar cells. This is primarily due to its unique properties, including a layer dependent wide energy bandgap, superior mechanical strength, high thermal conductivity, high band-edge absorption coefficient, and exceptional transparency in the UV region. The widely adopted synthesis method for h-BN thin films is Chemical Vapor Deposition (CVD) Method, which often utilizes catalytic substrates like copper (Cu) and Nickel (Ni). However, integrating the synthesized h-BN into device applications requires a subsequent transfer process to the target substrate. This transfer step introduces significant material damage, such as folding, cracking and polymer residues, which ultimately degrade the optoelectronic properties of the material and compromise device performance. To overcome this major challenge, there is a strong need to synthesize high-quality h-BN films directly onto dielectric substrates such as silicon (Si), SiO2, quartz, sapphire or AlN without the need for transfer. The primary difficulty in direct synthesis lies in achieving homogenous, high crystallinity films with controllable thickness due to the absence of a catalytic effect. In this work, we investigated the optimization of growth parameters for the direct synthesis of ultrathin h-BN films on non-catalytic quartz substrates, which are highly transparent in the UV region, using the Low-pressure Chemical Vapor Deposition (LPCVD) method. The optimal synthesis conditions were determined to be 1050oC for 60 min, achieved by the decomposition of 150 mg Ammonia Borane (AB) precursor at 80oC. This optimization is crucial for advancing large-scale, high-performance h-BN based DUV photodetector fabrication.