Optical Properties of Semiconducting Boron Carbide for Neutron Detection Applications

Solid state neutron detection devices based on semiconducting boron carbide have the potential for nearly ideal neutron detection effciency for thermal neutrons. The present work is focused on characterizing optical properties of this semiconducting boron carbide material as a step in further development of the material for neutron detection and other applications. Semiconducting boron carbide films were grown on silicon substrates using plasma enhanced chemical vapor deposition and their optical properties were characterized using variable angle spectroscopic ellipsometry over a wide spectral range, from mid-infrared to vacuum-ultraviolet wavelengths. The effects of deposition substrate temperature and of post-deposition heat treatments on the optical properties of these films were investigated. Quantitative material parameters, such as the infrared resonant frequencies and optical band gaps, were obtained using parameterized line shape models and regression analysis. Clear evidence was found for the incorporation of hydrogen in the boron carbide films during deposition, and for hydrogen elimination and the development of an icosahedral structural signature during annealing. X-ray diffraction and transmission electron microscopy techniques were also used to characterize the structural properties of the boron carbide films