Abstract
Hexagonal boron nitride (h-BN) is an attractive wide-bandgap material for application to emitters and detectors operating in the deep ultraviolet (DUV) spectral region. The optical transmittance of h-BN in the DUV region is particularly important for these devices. We report on the deposition of thick h-BN films (>200 nm) on Al0.7Ga0.3N templates via radio-frequency sputtering, along with the realization of ultrahigh transmittance in the DUV region. The fraction of the gas mixture (Ar/N2) was varied to investigate its effects on the optical transmittance of BN. DUV light transmittance of as high as 94% was achieved at 265 nm. This value could be further enhanced to exceed 98% by a post-annealing treatment at 800 °C in a N2 ambient for 20 min. The phase of the highly DUV–transparent BN film was determined to be a purely hexagonal structure via Raman spectra measurements. More importantly, these deposition processes were performed at a low temperature (300 °C), which can provide protection from device performance degradation when applied to actual devices.
Highlights
In recent years, AlGaN-based ultraviolet and deep ultraviolet (DUV) light-emitting diodes (LEDs) have attracted considerable interest among the efforts to replace toxic mercury lamps in a broad range of applications, including water/air purification, sterilization, and medical devices [1,2,3]
We report the realization of thick Hexagonal boron nitride (h-BN) layers with high transmittance in the DUV region on an Al0.7 Ga0.3 N template that were deposited by radio frequency (RF) magnetron sputtering under low temperature conditions
We anticipated that the h-BN could be integrated with current AlGaN-based DUV optoelectronic devices and the specific template composition was selected to be identical to that of the p-type Al0.7 Ga0.3 N cladding layer that is typically used in 260–280 nm DUV LEDs [28]
Summary
AlGaN-based ultraviolet and deep ultraviolet (DUV) light-emitting diodes (LEDs) have attracted considerable interest among the efforts to replace toxic mercury lamps in a broad range of applications, including water/air purification, sterilization, and medical devices [1,2,3]. It has been reported that the boron vacancies are acceptor-like defects with an energy level of approximately 150 meV above the valence band edge [13]. H-BN has an ideal band alignment to Al0.7 Ga0.3 N that allows it to act as a p-cladding layer for both hole injection and electron blocking [15]. These properties mean that h-BN is a promising candidate material for use as a p-type layer in optical devices.
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