Room-temperature intrinsic excitonic luminescence from a hexagonal boron nitride thin film grown on a sapphire substrate by low-pressure chemical vapor deposition using BCl₃ as a boron source

Abstract

A hexagonal boron nitride thin film was prepared on a c-plane sapphire substrate at a substrate temperature of 1200 °C and a reactor pressure of 5 kPa by chemical vapor deposition using BCl 3 as a boron source. The film, consisting of columnar grains with flat top surfaces, grew epitaxially on the substrate. This sample showed pronounced intrinsic exciton cathodoluminescence (CL) at 215 nm at room temperature, although broad emission at around 350 nm was dominant. Note that the spectrum shape in the band edge region closely matched that observed for a high-quality bulk crystal in terms of peak wavelength and width. The CL images of the surface revealed the correlation between the film structure and the luminescence property, where the intrinsic excitonic luminescence was exhibited only from the columnar grains, whereas the impurity-and/or the defect-related emissions were observed mainly from surface defects with randomly oriented grains.

Reduction in Residual Impurities in Chemical Vapor Deposition–Grown Hexagonal Boron Nitride Thin Films

“…[ 37 ] It can be seen that a narrow emission line at the higher energy emission (5.79 eV) in ×50 enlarged graph, which relates to the free excitonic recombination. [ 2,12,26,30,38,39 ] The 5.79 eV peak is not seen in the previous report, [ 24 ] which is owing to the reduction in residual impurities. Taniguchi and Watanabe obtained a strong free‐exciton luminescence at 5.79 eV by suppressing carbon and oxygen contamination in HTHP‐grown bulk h‐BN.…”

“…Its shoulder at 5.30 eV emission is most likely related to the quasi donor-acceptor pairs (q-DAP) [37]. It can be seen that a narrow emission line at the higher energy emission (5.79 eV) in Â50 enlarged graph, which relates to the free excitonic recombination [2,12,26,30,38,39]. The 5.79 eV peak is not seen in the previous report,[24] which is owing to the reduction in residual…”

“…So far, CVD-grown BN thin films have been demonstrated on various substrates, including sapphire, [4][5][6]8,[10][11][12][13][14][15][16][17][18][19][20][21]26] Cu, [7] Ni, [9,20,30] SiC, [8,21] GaN, [29] and Si. [27,28,31] The boron precursors include borazine (B 3 N 3 H 6 ), [7] boron halides (BF 3 , BCl 3 , BBr 3 ), [9,11,26,30] metal-organic (MO) of triethylboron [(C 2 H 5 ) 3 B, TEB], [4][5][6]10,[12][13][14][15][16][17][18][19][20] trimethylboron [(CH 3 ) 3 B, TMB], [21,25] and diborane (B 2 H 6 ). [8,9,…”

“…Among various 2D materials, hexagonal boron nitride (h‐BN) is expected for deep ultraviolet light‐emitting devices [ 1,2 ] and gate dielectric layer for graphene transistors. [ 3 ] There are various growth methods for growing BN films, such as high‐temperature and high‐pressure (HTHP) method, [ 2 ] thermal chemical vapor deposition (CVD), [ 4–26 ] plasma‐assisted CVD, [ 27–31 ] and molecular beam epitaxy (MBE). [ 32 ] Among them, CVD growth is suitable for heteroepitaxy devices in terms of mass production.…”

“…So far, CVD‐grown BN thin films have been demonstrated on various substrates, including sapphire, [ 4–6,8,10–21,26 ] Cu, [ 7 ] Ni, [ 9,20,30 ] SiC, [ 8,21 ] GaN, [ 29 ] and Si. [ 27,28,31 ] The boron precursors include borazine (B 3 N 3 H 6 ), [ 7 ] boron halides (BF 3 , BCl 3 , BBr 3 ), [ 9,11,26,30 ] metal–organic (MO) of triethylboron [(C 2 H 5 ) 3 B, TEB], [ 4–6,10,12–20 ] trimethylboron [(CH 3 ) 3 B, TMB], [ 21,25 ] and diborane (B 2 H 6 ). [ 8,9,22–24,27,28,31 ]…”