The boron phosphide (BP) semiconductor has many remarkable features, including high thermal neutron capture cross section of the 10 B isotope, making it attractive for neutron detection applications. Effective and efficient neutron detection require BP to also have high crystal quality with optimum electrical properties. Here, we present the heteroepitaxial growth of high quality BP films on a superior aluminum nitride(0001)/sapphire substrate by chemical vapor deposition. The effect of process variables on crystalline and morphological properties of BP was examined in detail. BP deposited at high temperatures and high reactant flow rate ratios produced films with increased grain size and improved crystalline orientation. Narrower full width at half-maximum values of BP Raman peaks (6.1 cm −1 ) and ω rocking curves (352 arcsec) compared to values in the literature confirm the high crystalline quality of produced films. The films were n-type with the highest electron mobility of 37.8 cm 2 /V·s and lowest carrier concentration of 3.15 × 10 18 cm −3 . Rotational twinning in BP due to degenerate epitaxy caused by 3-fold BP(111) on 6-fold AlN(0001) was confirmed by synchrotron white beam X-ray topography. This preliminary study showed that AlN is an excellent substrate for growing high quality BP epitaxial films with promising potential for further enhancement of BP properties.

a b s t r a c tEpitaxial growth of boron phosphide (BP) films on 4H-and 6H-SiC(0001) substrates with on-and off-axis orientations was investigated in this study. The films were prepared by chemical vapor deposition using phosphine and diborane as reactants over a temperature range of 1000 o Ce1200 C. The effects of growth parameters such as temperature, reactant flow rates, substrate type, and crystallographic orientation on BP film properties were studied in detail. The epitaxial relationship between BP film and 4H-and 6H-SiC substrate was ð111ÞBP < 112 > BP jj ð0001ÞSiC < 1100 > SiC. Film quality, determined by preferred crystalline orientation and grain size, improved with temperature and PH 3 /B 2 H 6 flow ratio, as indicated by scanning electron microscopy, x-ray diffraction, atomic force microscopy and Raman spectroscopy. In addition, smoother films were obtained when the diborane flow rate was reduced. Rotational twinning in BP films was absent on 4H-SiC(0001) tilted 4 towards ½1100, but was confirmed on both 4H-SiC(0001) tilted 4 towards ½1210, and on-axis 6H-SiC(0001) substrates by synchrotron white beam x-ray topography technique.

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Icosahedral boron phosphide (B 12 P 2) is a wide bandgap semiconductor (3.35 eV) that has been reported to "selfheal" from high-energy electron bombardment, making it attractive for potential use in radioisotope batteries, radiation detection, or in electronics in high radiation environments. This study focused on improving B 12 P 2 hetero-epitaxial films by growing on 4H-SiC substrates over the temperature range of 1250-1450 • C using B 2 H 6 and PH 3 precursors in a H 2 carrier gas. XRD scans and Laue transmission photographs revealed that the epitaxial relationship was (0001) 1120 B 12 P 2 (0001) 1120 4H-SiC. The film morphology and crystallinity were investigated as a function of growth temperature and growth time. At 1250 • C, films tended to form rough, polycrystalline layers, but at 1300 and 1350 • C, films were continuous and comparatively smooth (R RMS ≤ 7 nm). At 1400 or 1450 • C, the films grew in islands that coalesced as the films became thicker. Using XRD rocking curves to evaluate the crystal quality, 1300 • C was the optimum growth temperature tested. At 1300 • C, the rocking curve FWHM decreased with increasing film thickness from 1494 arcsec for a 1.1 μm thick film to 954 arcsec for a 2.7 μm thick film, suggesting a reduction in defects with thickness.

We employ X-ray absorption near-edge spectroscopy at the boron K-edge and the phosphorus L-edge to study the structural properties of cubic boron phosphide (c-BP) samples. The X-ray absorption spectra are modeled from first-principles within the density functional theory framework using the excited electron core-hole (XCH) approach. A simple structural model of a perfect c-BP crystal accurately reproduces the P L-edge, however it fails to describe the broad and gradual onset of the B K-edge. Simulations of the spectroscopic signatures in boron 1s excitations of intrinsic point defects and the hexagonal BP crystal phase show that these additions to the structural model cannot reproduce the broad pre-edge of the experimental spectrum. Calculated formation enthalpies show that, during the growth of c-BP, it is possible that amorphous boron phases can be grown in conjunction with the desired boron phosphide crystalline phase. In combination with experimental and theoretically obtained X-ray absorption spectra of an amorphous boron structure, which have a similar broad absorption onset in the B K-edge spectrum as the cubic boron phosphide samples, we provide evidence for the presence of amorphous boron clusters in the synthesized c-BP samples.