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Thin films of the sp(2)-hybridized polytypes of boron nitride (BN) are interesting materials for several electronic applications such as UV devices. Deposition of epitaxial sp(2)-BN films has been demonstrated on several technologically important semiconductor substrates such as SiC and Al2O3 and where controlled thin film growth on Si would be beneficial for integration of sp(2)-BN in many electronic device systems. The authors investigate the growth of BN films on Si(111) by chemical vapor deposition from triethylboron [B(C2H5)(3)] and ammonia (NH3) at 1300 degrees C with focus on treatments of the Si(111) surface by nitridation, carbidization, or nitridation followed by carbidization prior to BN growth. Fourier transform infrared spectroscopy shows that the BN films deposited exhibit sp(2) bonding. X-ray diffraction reveals that the sp(2)-BN films predominantly grow amorphous on untreated and pretreated Si(111), but with diffraction data showing that turbostratic BN can be deposited on Si(111) when the formation of Si3N4 is avoided. The authors accomplish this condition by combining the nitridation procedure with reactions from the walls on which BxC had previously been deposited. ; Funding Agencies|Swedish Foundation for Strategic Research (SSF)Swedish Foundation for Strategic Research [IS14-0027]; Swedish Government Strategic Research Area in Materials Science on Advanced Functional Materials at Linkoping University [SFO-Mat-LiU 2009-00971]

Epitaxial rhombohedral boron nitride (r-BN) films were deposited on alpha-Al2O3(001) substrates by chemical vapor deposition, using trimethylboron, ammonia, and a low concentration of silane in the growth flux. The depositions were performed at temperatures from 1200 to 1485 degrees C, pressures from 30 to 90 mbar, and N/B ratios from 321 to 1286. The most favorable conditions for epitaxy were a temperature of 1400 degrees C, N/B around 964, and pressures below 40 mbar. Analysis by thin film x-ray diffraction showed that most deposited films were polytype-pure epitaxial r-BN with an out-of-plane epitaxial relationship of r-BN[001] parallel to w-AlN[001] parallel to alpha-Al2O3[001] and with two in-plane relationships of r-BN[110] parallel to w-AlN[110] parallel to alpha-Al2O3[100] and r-BN[110] parallel to w-AlN[110] parallel to alpha-Al2O3[(1) over bar 00] due to twinning. Published by the AVS. ; Funding Agencies|Swedish Foundation for Strategic Research (SSF) [IS14-0027]; Swedish Government Strategic Research Area in Materials Science on Advanced Functional Materials at Linkoping University [2009-00971]

Thin films of boron nitride in its sp(2)-hybridized form (sp(2)-BN) have potential uses in UV devices and dielectrics. Here, we explore chemical vapor deposition (CVD) of sp(2)-BN on various cuts of sapphire: Al2O3 ( 11 2 over bar 0 ), Al2O3 ( 1 1 over bar 02 ), Al2O3 ( 10 1 over bar 0 ), and Al2O3 (0001) using two CVD processes with two different boron precursors triethylborane and trimethylborane. Fourier transform infrared spectroscopy shows that sp(2)-BN grows on all the sapphire substrates; using x-ray diffraction, 2 theta/omega diffractogram shows that only Al2O3 ( 11 2 over bar 0 ) and Al2O3 (0001) rendered crystalline films: and using phi(phi)-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 over bar 0 ) substrate, which is determined using omega(omega)-scans. Our study suggests that Al2O3 ( 11 2 over bar 0 ) is the most favorable sapphire substrate to realize the envisioned applications of r-BN films. ; Funding Agencies|Swedish Research Council [2017-04164]; Swedish Foundation for Strategic Research (SSF) [IS14-0027]; Carl Tryggers Foundation for Scientific Research [CTS 14:189]; Swedish Government Strategic Research Area in Materials Science on Advanced Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]; Swedish Research Council VR-RFI [2019-00191]; Swedish Foundation for Strategic Research [RIF14-0053]

Amorphous boron-carbon-nitrogen (B-C-N) films with low density are potentially interesting as alternative low-dielectric-constant (low-kappa) materials for future electronic devices. Such applications require deposition at temperatures below 300 degrees 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 kappa, 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. ; Funding Agencies|Swedish Foundation for Strategic Research (SSF)Swedish Foundation for Strategic Research [IS14-0027]; Swedish Government Strategic Research Area in Materials Science on Advanced Functional Materials at Linkoping University [2009-00971]; Swedish research council VR-RFISwedish Research Council [2017-00646_9]; Swedish Foundation for Strategic ResearchSwedish Foundation for Strategic Research [RIF14-0053]; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation

Epitaxial rhombohedral boron nitride (r-BN) films were deposited on ZrB2(0001)/4H-SiC(0001) by chemical vapor deposition at 1485 degrees C from the reaction of triethylboron and ammonia and with a minute amount of silane (SiH4). X-ray diffraction (XRD) w-scans yield the epitaxial relationships of r-BN(0001) k ZrB2(0001) out-of-plane and r-BN[11-20] k ZrB2[11-20] in-plane. Cross-sectional transmission electron microscopy (TEM) micrographs showed that epitaxial growth of r-BN films prevails to similar 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. ; Funding Agencies|Swedish Foundation for Strategic Research (SSF)Swedish Foundation for Strategic Research [IS14-0027]; Carl Tryggers Foundation for Scientific Research [CTS 14:189]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]

Boron nitride (BN) layers with sp(2) bonding have been grown by metal organic chemical vapor deposition on AlN underlayers, which are deposited on c-plane sapphire substrates. Two different boron precursors were employed-trimethylboron and triethylboron-while ammonia was used as the nitrogen precursor. The BN obtained epitaxial BN films contain ordered rhombohedral (rBN) and partially ordered turbostratic (tBN) stackings as evidenced by x-ray diffraction analysis. We discriminatively identify the PL signatures of the rBN and tBN from those typical of the hexagonal (hBN) and Bernal stackings (bBN). The optical signature of tBN appears at 5.45eV, and it intercalates between the two recombination bands typical of rBN at 5.35eV (strong intensity) and 5.55eV(weaker intensity). The analogs of the high intensity band at 5.35eV in rBN sit at 5.47eV for hBN and at 5.54eV for bBN. ; Funding Agencies|network GaNeX [ANR-11-LABX-424 0014]; BONASPES project [ANR-19-CE30 0007]; ZEOLIGHT project [ANR-19-CE08-0016]; Universite de Montpellier; Swedish Research CouncilSwedish Research CouncilEuropean Commission [2017-04164]; Swedish Foundation for Strategic Research (SSF)Swedish Foundation for Strategic Research [IS14-0027]; Carl Tryggers Foundation for Scientific Research [CTS 14:189]; Swedish Government Strategic Research Area in Materials Science on Advanced Functional Materials at Linkoping University [2009-00971]; Office of Naval ResearchOffice of Naval Research [N00014-20-1-2474, 428]; National Science FoundationNational Science Foundation (NSF) [CMMI 429, 1538127]

Alkylboranes, such as trimethylboron (TMB) and triethylboron (TEB), are promising alternative precursors in low temperature chemical vapor deposition (CVD) of boron-containing thin films. In this study, CVD growth of B-C films using TMB and quantum-chemical calculations to elucidate a gas phase chemical mechanism were undertaken. Dense, amorphous, boron-rich (B/C 1.5-3) films were deposited at 1000 degrees C in both dihydrogen and argon ambients, while films with crystalline B4C and B25C inclusions were deposited at 1100 degrees C in dihydrogen. A script-based automatization scheme was implemented for the quantum-chemical computations to enable time efficient screening of thousands of possible gas phase CVD reactions. The quantum-chemical calculations suggest TMB is mainly decomposed by an unimolecular alpha-H elimination of methane, which is complemented by dihydrogen-assisted elimination of methane in dihydrogen. ; Funding Agencies|European Spallation Source ERIC; Knut and Alice Wallenberg Foundation; German Science Foundation [GRK 1782]; Swedish Foundation for Strategic Research (SSF) [IS14-0027]; COST Action [MP1402]; COST (European Cooperation in Science and Technology); Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]