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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Bi-alkali antimonide photocathodes are the best known sources of electrons for high current and/or high bunch charge applications like Energy Recovery Linacs or Free Electron Lasers.Despite their high quantum efficiency in visible light and low intrinsic emittance, the surface roughness of these photocathodes prohibits their use as low emittance cathodes in high accelerating gradient superconducting and normal conducting radio frequency photoguns and limits the minimum possible intrinsic emittance near the threshold. Also, the growth process for these materials is largely based on recipes obtained by trial and error and is very unreliable. In this paper, using X-ray diffraction, we investigate the different structural and chemical changes that take place during the growth process of the bi-alkali antimonide material K 2 CsSb.Our measurements give us a deeper understanding of the growth process of alkaliantimonide photocathodes allowing us to optimize it with the goal of minimizing the surface roughness to preserve the intrinsic emittance at high electric fields and increasing its reproducibility.

K2CsSb is a promising photocathode candidate to serve as an electron source in next-generation light sources such as Free Electron Lasers (FEL) and Energy Recovery Linacs (ERL). As the traditional recipe for creation of K2CsSb photocathodes typically results in a rough surface that deteriorates electron beam quality, significant effort has been made to explore novel growth methods for K2CsSb photocathodes. In this paper, a method of ternary co-evaporation of K, Cs, and Sb is described. By using in-situ synchrotron X-ray techniques, the quality of the photocathode is characterized during and after the growth. K2CsSb photocathodes grown by this method on Si (100) and MgO (001) substrates show strong (222) texture, and the two photocathodes exhibit 1.7% and 3.4% quantum efficiencies at a wavelength of 530 nm, with a rms surface roughness of about 2–4 nm. This represents an order of magnitude reduction in roughness compared to typical sequential deposition and should result in a significant improvement in the brightness of the generated electron beam.