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

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.