Status of h-BN semi-bulk crystals

III-nitride wide bandgap semiconductors have revolutionized the lighting industry and are poised to make a huge impact in power electronics. In the III-nitride family, the crystal growth and use of hexagonal BN (h-BN) as an ultrawide bandgap semiconductor (UWBG) are much less developed. The development of crystal growth technologies for producing semi-bulk crystals in large wafer sizes with high crystalline quality and low defect density is a prerequisite for utilizing h-BN as an UWBG electronic material. In addition to optoelectronic and electronic device applications, h-BN has another unique application for high efficiency solid-state neutron detectors because of an unusually large interaction cross-section between B-10 isotope and thermal neutrons, which however, also require the development of thick semi-bulk crystals.<br/><br/>In this talk, we provide a brief overview and recent progress toward the development of h-BN semi-bulk crystals by hydride vapor phase epitaxy (HVPE) and metal organic chemical vapor deposition (MOCVD). Benchmarking the crystalline and optical qualities of h-BN semi-bulk crystals with respect to the state-of-the-art millimeter-sized bulk crystal flakes grown by the high pressure/high temperature (HP/HT) and the metal flux solution methods together with photoluminescence (PL) emission and photocurrent excitation spectroscopy measurements identified that reducing the density of impurities and defects such as oxygen impurities and boron vacancies remains the most critical task for h-BN semi-bulk crystal growth. The performance of neutron detectors fabricated from semi-bulk h-BN wafers and the attainment of h-BN thermal neutron detectors with a record efficiency of 60% will also be presented. The development of high efficiency h-BN neutron detector technology serves as a stepstone for further advancing the crystal growth technology to produce electronic grade h-BN semi-bulk wafers.