Annealing effects on crystalline quality and device performance of ultrawide bandgap h-BN quasi-bulk crystals

Abstract

Hexagonal boron nitride (h-BN) is a notable member of ultrawide bandgap semiconductors, distinguished by its unique layered crystalline structure and exceptional electrical and optical properties. One of the established and important device applications of h-BN lies in solid-state neutron detectors. Achieving high detection efficiency requires thick, high-quality crystals to maximize neutron interactions and charge carrier collection. While hydride vapor phase epitaxy (HVPE) excels at growing thick, uniform h-BN films (quasi-bulk wafers), its high growth rate can compromise crystallinity by introducing structural defects. This study investigates the impact of post-growth high-temperature annealing (up to 1900 °C) on 1 mm thick HVPE-grown h-BN. X-ray diffraction confirmed significant improvements in crystallinity with higher annealing temperatures, leading to increased resistivity and an enhanced charge carrier mobility-lifetime product. A detector fabricated from h-BN annealed at 1900 °C demonstrated a 0.7% overall detection efficiency and 37% charge collection efficiency for fast neutrons from an AmBe source. These findings highlight post-growth annealing as a simple yet highly effective method to improve h-BN quality for a wide range of applications, including direct conversion solid-state neutron detectors, which are becoming increasingly vital in various nuclear diagnostic instruments.