Boron Phosphide Films Research Articles

Boron Phosphide Films by Reactive Sputtering: Searching for a P‐Type Transparent Conductor

Boron Phosphide Films by Reactive Sputtering: Searching for a P‐Type Transparent Conductor

Boron Phosphide Films by Reactive Sputtering: Searching for a P‐Type Transparent Conductor

AbstractWith an indirect band gap in the visible and a direct band gap at a much higher energy, boron phosphide (BP) holds promise as an unconventional p‐type transparent conductor. This work reports on reactive sputtering of amorphous BP films, their partial crystallization in a P‐containing annealing atmosphere, and extrinsic doping by C and Si. The highest hole concentration to date for p‐type BP (5 × 1020cm−3) is achieved using C doping under B‐rich conditions. Furthermore, bipolar doping is confirmed to be feasible in BP. An anneal temperature of at least 1000 °C is necessary for crystallization and dopant activation. Hole mobilities are low and indirect optical transitions are stronger than that predicted by theory. Low crystalline quality probably plays a role in both cases. High figures of merit for transparent conductors might be achievable in extrinsically doped BP films with improved crystalline quality.

Cubic boron phosphide epitaxy on zirconium diboride

Cubic boron phosphide (BP) is one of the least studied III-V compound semiconductors, in part because it is difficult to prepare in high quality form. In this study, zirconium diboride (ZrB2) was studied as a potential substrate for BP epitaxial layers, because of its advantages of a low lattice constant mismatch and high thermal stability. Two types of substrates were considered: ZrB2(0 0 0 1) epitaxial films on 4H-SiC(0 0 0 1) and bulk ZrB2(0 0 0 1) single crystals. The optimal temperature for epitaxy on these substrates was 1100 °C; higher and lower temperatures resulted in polycrystalline films. The BP film/ZrB2 interface was abrupt as confirmed by cross-sectional transmission electron microscopy, attesting to the stability of ZrB2 under BP deposition conditions. The BP films were under compressive and tensile strain on ZrB2 and ZrB2/4H-SiC substrates, respectively, as determined by Raman spectroscopy, due to differences in the substrate/film coefficients of thermal expansion. This study suggests that with further optimization, ZrB2 can be an excellent substrate for BP epitaxial films.

CVD growth and properties of boron phosphide on 3C-SiC

Improving the crystalline quality of boron phosphide (BP) is essential for realizing its full potential in semiconductor device applications. In this study, 3C-SiC was tested as a substrate for BP epitaxy. BP films were grown on 3C-SiC(100)/Si, 3C-SiC(111)/Si, and 3C-SiC(111)/4H-SiC(0001) substrates in a horizontal chemical vapor deposition (CVD) system. Films were produced with good crystalline orientation and morphological features in the temperature range of 1000–1200°C using a PH3+B2H6+H2 mixture. Rotational twinning was absent in the BP due to the crystal symmetry-matching with 3C-SiC. Confocal 3D Raman imaging of BP films revealed primarily uniform peak shift and peak widths across the scanned area, except at defects on the surface. Synchrotron white beam X-ray topography showed the epitaxial relationship between BP and 3C-SiC was (100)〈011〉BP||(100)〈011〉3C-SiC and (111)〈112̅〉BP||(111)〈112̅〉3C-SiC. Scanning electron microscopy, Raman spectroscopy and X-ray diffraction analysis indicated residual tensile strain in the films and improved crystalline quality at temperatures below 1200°C. These results indicated that BP properties could be further enhanced by employing high quality bulk 3C-SiC or 3C-SiC epilayers on 4H-SiC substrates.

Epitaxy of Boron Phosphide on Aluminum Nitride(0001)/Sapphire Substrate

The boron phosphide (BP) semiconductor has many remarkable features, including high thermal neutron capture cross section of the 10B 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 cm2/V·s and lowest carrie...

Preparation, properties, and characterization of boron phosphide films on 4H- and 6H-silicon carbide

Epitaxial 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 oC–1200 °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 (111)BP<112¯>BP||(0001)SiC<11¯00>SiC. Film quality, determined by preferred crystalline orientation and grain size, improved with temperature and PH3/B2H6 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 [11¯00], but was confirmed on both 4H-SiC(0001) tilted 4° towards [12¯10], and on-axis 6H-SiC(0001) substrates by synchrotron white beam x-ray topography technique.

Structure characterization and strain relief analysis in CVD growth of boron phosphide on silicon carbide

Boron phosphide (BP) is a material of interest for development of a high-efficiency solid-state thermal neutron detector. For a thick film-based device, microstructure evolution is key to the engineering of material synthesis. Here, we report epitaxial BP films grown on silicon carbide with vicinal steps and provide a detailed analysis of the microstructure evolution and strain relief. The BP film is epitaxial in the near-interface region but deviates from epitaxial growth as the film develops. Defects such as coherent and incoherent twin boundaries, dislocation loops, stacking faults concentrate in the near-interface region and segment this region into small domains. The formation of defects in this region do not fully release the strain originated from the lattice mismatch. Large grains emerge above the near-interface region and grain boundaries become the main defects in the upper part of the BP film.

Effect of gas flow ratio on the microstructure and mechanical properties of boron phosphide films prepared by reactive magnetron sputtering

Boron phosphide films were grown on silicon substrate by radio frequency reactive magnetron sputtering using boron target and hydrogen phosphine at different gas flow ratios (PH 3/Ar) at lower temperature. The chemical composition, microstructure and mechanical properties were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, Raman spectrum, FTIR spectrum, surface profilometer and nano-indenter. The results indicate that the atomic ratio (P/B) rises from 1.06 up to 1.52 with the gas flow ratio increasing from 3/50 to 15/50. Simultaneously, the hardness and Young's modulus decrease from 25.4 GPa to 22.5 GPa, and 250.4 GPa to 238.4 GPa, respectively. Microstructure transforms from microcrystalline state to amorphous state along with the gas flow ratio increasing. Furthermore higher gas flow ratio leads to lower stress. The BP film prepared at the gas flow ratio of 3/50 can be contributed with the best properties.

Synthesis of n-type boron phosphide films and formation of Schottky diode: Al/n-BP/Sb

Phosphorous rich BP in thin film form was deposited onto fused silica substrates by co-evaporating boron (99.99%) and phosphorous (99.995%) from a tantalum boat and indirectly heated alumina crucible, respectively. Schottky diode structures for n-type BP (Al/n-BP/Sb) were fabricated out of these films. Corresponding current–voltage and capacitance–voltage characteristics of the Schottky diodes were recorded and analyzed in the light of the existing theories.

Boron phosphide films prepared by co-evaporation technique: Synthesis and characterization

We report the physical and electronic properties of BP films of 1:1, 1:1.15 and 1.25:1 stoichiometry prepared by co-evaporating B and P onto glass and Si (100) substrates. Compositional information was obtained from X-ray photoelectron spectroscopy measurements. Optical studies indicated allowed indirect transition at ∼ 2.08 eV. The room temperature photoluminescence peak at ∼ 2.01 eV was due to band gap transitions which shifted to higher energy value when recorded at lower temperature. Fourier transformed infrared (FTIR) spectra were dominated by the characteristic peak of the B–P located at ∼ 810 cm − 1 which could be identified as arising due to transverse optical vibration mode ( k ∼ 0) while the shoulder at ∼ 850 cm − 1 may be due to longitudinal optical ( k ∼ 0) vibration mode. Other characteristic peaks for B–O, P–O and B–H vibration modes were also present in the FTIR spectra. Characteristic Raman peaks for BP located at ∼ 415 cm − 1 and 806 cm − 1 were observed in these films.

Thermoelectric properties of photo- and thermal CVD boron and boron phosphide films

The electrical properties of n-BP films newly prepared by thermal CVD in the B 2H 6–PH 3–H 2 system were improved by a deuterium lamp excitation. High-temperature electrical conductivity and thermoelectric power of amorphous boron and polycrystalline boron phosphide films grown on silica glass were measured to evaluate the thermoelectric figure-of-merit ( Z). In particular, the Z-value for photo-thermal BP films was higher (10 −4/K) than that of boron films, indicating that they are promising for high-temperature thermoelectric materials.

Thermoelectric properties of photo-thermal CVD boron and boron phosphide films

Thermoelectric properties of photo-thermal CVD boron and boron phosphide films

Preparation of Boron and Boron Phosphide Films by Photo- and Thermal Chemical Vapor Deposition Processes

We have calculated first excitation energies, oscillator strengths, and potential energy surfaces of B2H6 and PH3 by using an ab initio molecular orbital method to confirm that the deuterium lamp is effective for the excitation of both B2H6 and PH3 in the photo-chemical vapor deposition (photo-CVD) process. The deuterium lamp is useful for growing the film at 600–1000°C in the B2H6–PH3–H2 system. The activation energies for film growth for thermal CVD decrease by using the deuterium lamp. Boron phosphide film grew epitaxially on Si(100) plane with a deuterium lamp at lower temperature than by thermal CVD at 100°C. The electrical properties of boron and boron phosphide films on silica glass were improved by deuterium.

Thermoelectric Properties of Boron and Boron Phosphide Films

Amorphous boron and boron phosphide films were prepared on silica glass by a solid source molecular beam deposition (SSMBD) method and a low-pressure chemical vapor deposition method (LPCVD) by adapting gas source molecular beam deposition at a reactant pressure of 1.33 Pa. The films were characterized by X-ray diffraction, X-ray photon electron spectroscopy (XPS), and Hall effect measurements. The experimental results on film growth were correlated with the calculation by an ab initio molecular orbital method. The high-temperature electrical conductivity and thermoelectric power of these films were measured to evaluate the thermoelectric figure-of-merit (Z), which was determined by the electrical conductivity of the films. In particular, the Z value for SSMBD boron and LPCVD boron phosphide films was higher (10−5/K) than those of LPCVD boron films, indicating that they are promising high-temperature thermoelectric materials.

Preparation and Electrical Properties of Boron and Boron Phosphide Films Obtained by Gas Source Molecular Beam Deposition

Boron and boron phosphide films were prepared by gas source molecular beam deposition on sapphire crystal at various substrate temperatures up to 800°C using cracked B2H6(2% in H2) at 300°C and cracked PH3(20% in H2) at 900°C. The substrate temperatures and gas flow rates of the reactant gases determined the film growth. The boron films with amorphous structure areptype. Increasing growth times lead to increasing mobilities and decreasing carrier concentrations. Boron phosphide film with maximum P/B ratio is obtained at a substrate temperature of 600°C, below and above which they become phosphorus deficient due to insufficient supply of phosphorus and thermal desorption of the phosphorus as P2, respectively, but they are allntype conductors due to phosphorus vacancies.

Amorphous Silicon Solar Cell and Boron Phosphide Thin Films Analyzed by FTIR and ESR.

Thin films of three layers (p-type/i-type/n-type) amorphous silicon (a-Si:H) and boron phosphide (BP) were investigated by means of Fourier transform infra-red (FTIR) spectroscopy and electron spin resonance (ESR). The formation ratio of (B-H)/(P-H) bonds in BP film, as functions of SiH, and PH3 gas flows, was evaluated by magnitude of stretching vibration. As for a-Si, higher order bond of-(Si-H2)-n, which may deteriorate the efficiency of solar energy conversion (ESEC), was distinguishable from Si-H single bond. The number of unpaired electron spins formed in 5 % ESEC a-Si:H, 7.99-1013 (spin/gram), was 73% larger than that in 8% ESEC a-Si:H.

Thermoelectric Properties of Boron and Boron Phosphide Film

ABSTRACTThis paper describes the thermoelectric properties of amorphous or polycrystalline boron and boron phosphide films prepared using chemical vapor deposition and molecular beam deposition. The temperature dependencies of electrical conductivity of a-B and distorted B13P2 films obey the Mott's rule of loga vs T-1/4, while those of polycrystalline BP films have linear relationship between loga vs T-1. The a-B and B13P2 films have high electric resistivity and show p-type conductors while BP film shows n-type conductor. The estimated thermoelectric figure of merit of boron phosphide film is compatible to that of sintered specimen, but there remains some problems for a-B to alter.

ChemInform Abstract: The Use of Metalorganics in the Preparation of Semiconductor Materials. Part 8. Feasibility Studies of the Growth of Group III‐Group V Compounds of Boron by MOCVD.

AbstractTrimethylborane (TMB) and triethylborane (TEB) in combination with AsH3 or PH3 in a H2 atmosphere are used as sources for the chemical vapor deposition of boron arsenide and boron phosphide films.