Role of Pressure in the Growth of Hexagonal Boron Nitride Thin Films from Ammonia-Borane

TL;DR

This study investigates how background pressure influences the quality and growth rate of hexagonal boron nitride thin films produced via chemical vapor deposition using ammonia-borane, revealing optimal conditions for crystalline film growth.

Contribution

It demonstrates that maintaining background pressure below 2.0 Torr and controlling precursor flux are crucial for producing high-quality, crystalline h-BN films with ammonia-borane in CVD processes.

Findings

Films at P_{TOT} < 2.0 Torr are uniform and highly crystalline.

Higher P_{TOT} leads to amorphous, disordered h-BN.

Growth rate increases with pressure but affects film quality.

Abstract

We analyze the optical, chemical, and electrical properties of chemical vapor deposition (CVD) grown hexagonal boron nitride (h-BN) using the precursor ammonia-borane ($H_3N-BH_3$) as a function of $Ar/H_2$ background pressure ($P_{TOT}$). Films grown at $P_{TOT}$ less than 2.0 Torr are uniform in thickness, highly crystalline, and consist solely of h-BN. At larger $P_{TOT}$, with constant precursor flow, the growth rate increases, but the resulting h-BN is more amorphous, disordered, and $sp^3$ bonded. We attribute these changes in h-BN grown at high pressure to incomplete thermolysis of the $H_3N-BH_3$ precursor from a passivated Cu catalyst. A similar increase in h-BN growth rate and amorphization is observed even at low $P_{TOT}$ if the $H_3N-BH_3$ partial pressure is initially greater than the background pressure $P_{TOT}$ at the beginning of growth. h-BN growth using the $H_3N-BH_3$ precursor reproducibly can give large-area, crystalline h-BN thin films, provided that the total pressure is under 2.0 Torr and the precursor flux is well-controlled.