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Rhombohedral boron carbide, often referred to as r-B4C, is a potential material for applications in optoelectronic and thermoelectric devices. From fundamental thin film growth and characterization, we investigate the film-substrate interface between the r-B4C films grown on 4H-SiC (0001¯) (C-face) and 4H-SiC (0001) (Si-face) during chemical vapor deposition (CVD) to find the origin for epitaxial growth solely observed on the C-face. We used high-resolution (scanning) transmission electron microscopy and electron energy loss spectroscopy to show that there is no surface roughness or additional carbon-based interlayer formation for either substrate. Based on Raman spectroscopy analysis, we also argue that carbon accumulation on the surface hinders the growth of continued epitaxial r-B4C in CVD. [ABSTRACT FROM AUTHOR]

Although it has long been known that metal-containing compounds can serve as catalysts for chemical vapor deposition (CVD) of films from other precursors, we show that metal-containing compounds can also inhibit CVD nucleation or growth. For two precursors A and B with growth onset temperatures TgA < TgB when used independently, it is possible that B can inhibit growth from A when the two precursors are coflowed onto a substrate at a temperature (T) where TgA < T < TgB. Here, we consider three precursors: AlH3⋅NMe3 (Tg = 130 °C, Me = CH3), Hf(BH4)4 (Tg = 170 °C), and AlMe3 (Tg = 300 °C). We find that (i) nucleation of Al from AlH3⋅NMe3 is inhibited by Hf(BH4)4 at 150 °C on two oxide surfaces (Si with native oxide and borosilicate glass), (ii) nucleation and growth of HfB2 is inhibited by AlMe3 at 250 °C on native oxide substrates and on HfB2 nuclei, and (iii) nucleation of Al from AlH3⋅NMe3 is inhibited by AlMe3 at 200 °C on native oxide substrates. Inhibition by Hf(BH4)4 is transient and persists only as long as its coflow is maintained; in contrast, AlMe3 inhibition of HfB2 growth is more permanent and continues after coflow is halted. As a result of nucleation inhibition, AlMe3 coflow enhances selectivity for HfB2 deposition on Au (growth) over Al2O3 (nongrowth) surfaces, and Hf(BH4)4 coflow makes it possible to deposit Al on Al nuclei and not on the surrounding oxide substrate. We propose the following criteria to identify candidate molecules for other precursor–inhibitor combinations: (i) the potential inhibitor should have a higher Tg than the desired film precursor, (ii) the potential inhibitor should be unreactive toward the desired film precursor, and (iii) at the desired growth temperature, the potential inhibitor should adsorb strongly enough to form a saturated monolayer on the intended nongrowth surface at accessible inhibitor pressures. [ABSTRACT FROM AUTHOR]

Boron carbide in its rhombohedral form (r-BxC), commonly denoted B4C or B13C2, is a well-known hard material, but it is also a potential semiconductor material. We deposited r-BxC by chemical vapor deposition between 1100 °C and 1500 °C from triethylboron in H2 on 4H-SiC(0001) and 4H-SiC(0001¯). We show, using ToF-ERDA, that pure B4C was grown at 1300 °C, furthermore, using XRD that graphite forms above 1400 °C. The films deposited above 1300 °C on 4H-SiC(0001¯) were found to be epitaxial, with the epitaxial relationships B4C(0001)[101¯0]‖4H-SiC(0001¯)[101¯0] obtained from pole figure measurements. In contrast, the films deposited on 4H-SiC(0001) were polycrystalline. We suggest that the difference in growth mode is explained by the difference in the ability of the different surfaces of 4H-SiC to act as carbon sources in the initial stages of the film growth. [ABSTRACT FROM AUTHOR]

Thin films of boron nitride in its sp2-hybridized form (sp2-BN) have potential uses in UV devices and dielectrics. Here, we explore chemical vapor deposition (CVD) of sp2-BN on various cuts of sapphire: Al2O3 (11 2 ¯ 0) , Al2O3 (1 1 ¯ 02) , Al2O3 (10 1 ¯ 0) , and Al2O3 (0001) using two CVD processes with two different boron precursors triethylborane and trimethylborane. Fourier transform infrared spectroscopy shows that sp2-BN grows on all the sapphire substrates; using x-ray diffraction, 2θ/ω diffractogram shows that only Al2O3 (11 2 ¯ 0) and Al2O3 (0001) rendered crystalline films: and using phi(ϕ)-scans, growth of the rhombohedral polytype (r-BN) films on these substrates is confirmed. These films were found to be epitaxially grown on an AlN interlayer with comparatively higher crystalline quality for the films grown on the Al2O3 (11 2 ¯ 0) substrate, which is determined using omega(ω)-scans. Our study suggests that Al2O3 (11 2 ¯ 0) is the most favorable sapphire substrate to realize the envisioned applications of r-BN films. [ABSTRACT FROM AUTHOR]

Epitaxial rhombohedral boron nitride (r-BN) films were deposited on ZrB2(0001)/4H-SiC(0001) by chemical vapor deposition at 1485 °C from the reaction of triethylboron and ammonia and with a minute amount of silane (SiH4). X-ray diffraction (XRD) φ-scans yield the epitaxial relationships of r - BN (0001) ∥ Zr B 2 (0001) out-of-plane and r - BN [ 11 2 ¯ 0 ] ∥ Zr B 2 [ 11 2 ¯ 0 ] in-plane. Cross-sectional transmission electron microscopy (TEM) micrographs showed that epitaxial growth of r-BN films prevails to ∼10 nm. Both XRD and TEM demonstrate the formation of carbon- and nitrogen-containing cubic inclusions at the ZrB2 surface. Quantitative analysis from x-ray photoelectron spectroscopy of the r-BN films shows B/N ratios between 1.30 and 1.20 and an O content of 3–4 at. %. Plan-view scanning electron microscopy images reveal a surface morphology where an amorphous material comprising B, C, and N is surrounding the epitaxial twinned r-BN crystals. [ABSTRACT FROM AUTHOR]

Amorphous boron–carbon–nitrogen (B–C–N) films with low density are potentially interesting as alternative low-dielectric-constant (low-κ) materials for future electronic devices. Such applications require deposition at temperatures below 300 °C, making plasma chemical vapor deposition (plasma CVD) a preferred deposition method. Plasma CVD of B–C–N films is today typically done with separate precursors for B, C and N or with precursors containing B–N bonds and an additional carbon precursor. We present an approach to plasma CVD of B–C–N films based on triethylboron (B(C2H5)3), a precursor with B–C bonds, in an argon–nitrogen plasma. From quantitative analysis with time-of-flight elastic recoil detection analysis (ToF-ERDA), we find that the deposition process can afford B–C–N films with a B/N ratio between 0.9–1.3 and B/C ratios between 3.4–8.6 and where the films contain from 3.6 to 7.8 at% H and from 6.6 to 20 at% O. The films have low density, from 0.32 to 1.6 g cm−3 as determined from cross-section scanning electron micrographs and ToF-ERDA with morphologies ranging from smooth films to separated nanowalls. Scanning transmission electron microscopy shows that C and BN do not phase-separate in the film. The static dielectric constant κ, measured by capacitance–voltage measurements, varies with the Ar concentration in the range from 3.3 to 35 for low and high Ar concentrations, respectively. We suggest that this dependence is caused by the energetic bombardment of plasma species during film deposition. [ABSTRACT FROM AUTHOR]

Rhombohedral boron carbide, often referred to as r-B 4 C, is a potential material for applications in optoelectronic and thermoelectric devices. From fundamental thin film growth and characterization, we investigate the film-substrate interface between the r-B 4 C films grown on 4H-SiC (0001̄) (C-face) and 4H-SiC (0001) (Si-face) during chemical vapor deposition (CVD) to find the origin for epitaxial growth solely observed on the C-face. We used high-resolution (scanning) transmission electron microscopy and electron energy loss spectroscopy to show that there is no surface roughness or additional carbon-based interlayer formation for either substrate. Based on Raman spectroscopy analysis, we also argue that carbon accumulation on the surface hinders the growth of continued epitaxial r-B 4 C in CVD.