Comparative Study of Boron Precursors for Chemical Vapor‐Phase Deposition‐Grown Hexagonal Boron Nitride Thin Films

Abstract

Two different boron precursors, diborane (B2H6) and trimethyl boron ((CH3)3B, TMB), are investigated for chemical vapor‐phase deposition (CVD)‐grown hexagonal boron nitride (h‐BN) on α‐Al2O3 (0001) substrates. The BN layer grown using TMB includes a large amount (2 × 1020 cm−3) of carbon atoms, which is 60 times higher than that in the BN layer grown using B2H6. The X‐ray diffraction 2θ/ω scans for BN film grown using B2H6 exhibit the h‐BN (002) peak. The BN film obtained using TMB includes turbostratic BN (t‐BN). The E2g Raman peak frequencies in B2H6 and TMB h‐BN are observed at 1368.8 and 1369.7 cm−1, respectively. The Raman peak shift to a higher frequency indicates that a larger compressive strain is induced using TMB than using B2H6. The full width at half maximum of the B2H6 and TMB Raman peak frequencies is 21.8 and 42.7 cm−1, respectively. The cathodoluminescence spectra of B2H6 h‐BN show the band‐edge emissions at 225 and 232 nm, whereas only a 300 nm broadband is obtained in TMB h‐BN. It is suggested that the carbon atoms in TMB prevent the formation of highly crystalline h‐BN thin films.