Comparative Study of Boron Precursors for Chemical Vapor‐Phase Deposition‐Grown Hexagonal Boron Nitride Thin Films
Hisashi Yamada, Sho Inotsume, Naoto Kumagai, Toshikazu Yamada, Mitsuaki Shimizu
Abstract
Two different boron precursors, diborane (B 2 H 6 ) and trimethyl boron ((CH 3 ) 3 B, TMB), are investigated for chemical vapor‐phase deposition (CVD)‐grown hexagonal boron nitride ( h ‐BN) on α‐Al 2 O 3 (0001) substrates. The BN layer grown using TMB includes a large amount (2 × 10 20 cm −3 ) of carbon atoms, which is 60 times higher than that in the BN layer grown using B 2 H 6 . The X‐ray diffraction 2 θ / ω scans for BN film grown using B 2 H 6 exhibit the h ‐BN (002) peak. The BN film obtained using TMB includes turbostratic BN ( t ‐BN). The E 2g Raman peak frequencies in B 2 H 6 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 B 2 H 6 . The full width at half maximum of the B 2 H 6 and TMB Raman peak frequencies is 21.8 and 42.7 cm −1 , respectively. The cathodoluminescence spectra of B 2 H 6 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.