(809f) Epitaxial Growth of Thick Films of Boron Phosphide On Silicon Carbide and Its Properties

Boron phosphide (BP) is potentially useful in solid state neutron detectors because of the large thermal neutron capture cross-section of the boron-10 isotope. In the CVD growth of BP films, various problems related to the film cracking due to the difference in thermal expansion coefficients & lattice mismatch and incorporation of the substrate impurities into the film have been reported in the literature. Silicon carbide (SiC) is a superior substrate in terms of lattice match, thermal expansion coefficient and chemical stability which would eliminate the above problems. In this work, cubic BP was epitaxially grown on the various types of SiC substrates by thermal decomposition of a B₂H₆-PH₃ mixture in hydrogen in the CVD furnace in the temperature range of 1100°C to 1200°C and 700 torr pressure. We have succeeded in obtaining single crystal BP films on conducting as well as insulating SiC substrates with 15 microns of thickness. The effect of growth parameters such as substrate type and orientation, temperature, and reactant compositions on the structural and electrical properties of the films was examined. The intentionally misoriented substrates are investigated for their potential to eliminate dislocations and inverse domain boundaries. The best BP single crystal was grown at 1200⁰C with (111) face on the 4H-SiC (4⁰ off-axis). X-Ray Diffraction showed that the BP films are highly crystalline with FWHM of the narrowest peak (111) is 0.1, which is the narrowest ever reported. The Raman spectroscopy showed intense, sharp phonon peaks located at 821 cm^-1. Electron microscopy revealed smooth surface of the film. The electrical properties of the films grown on electrically insulating 4H-SiC substrate were also studied. Thus, the high crystal quality, low defect densities and desired electrical properties of these BP films will make them best suitable for fabricating the neutron detection devices.