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

摘要

Two different boron precursors, diborane (B_2H_6) and trimethyl boron((CH_3)_3B, TMB), are investigated for chemical vapor-phase deposition(CVD)-grown hexagonal boron nitride (h-BN) on α-Al_2O_3 (0001) substrates. TheBN layer grown using TMB includes a large amount (2 × 10~(20) cm~(-3)) of carbonatoms, which is 60 times higher than that in the BN layer grown using B_2H_6.The X-ray diffraction 2θ/ω scans for BN film grown using B_2H_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_2H_6 and TMBh-BN are observed at 1368.8and 1369.7 cm~(-1), respectively. The Raman peak shift to a higher frequencyindicates that a larger compressive strain is induced using TMB than using B_2H_6.The full width at half maximum of the B2H6 and TMB Raman peak frequencies is21.8 and 42.7 cm~(-1), respectively. The cathodoluminescence spectra of B_2H_6 h-BNshow the band-edge emissions at 225 and 232 nm, whereas only a 300 nmbroadband is obtained in TMBh-BN. It is suggested that the carbon atoms in TMBprevent the formation of highly crystalline h-BN thin films.