High Reflectivity YDH/SiO2 Distributed Bragg Reflector for UV-C Wavelength Regime

A distributed Bragg reflector (DBR) composed of Y
₂
O
₃
-doped HfO
₂
(YDH)/SiO
₂
layers with high reflectivity spectrum centered at a wavelength of ~240 nm is fabricated using radio-frequency magnetron sputtering. Before the DBR deposition, optical properties for a single layer of YDH, SiO
₂
, and HfO
₂
thin films were studied using spectroscopic ellipsometry and spectrophotometry. To investigate the performance of YDH as a material for the high refractive index layer in the DBR, a comparison of its optical properties was made with HfO
₂
thin films. Due to larger optical bandgap, the YDH thin films demonstrated higher transparency, lower extinction coefficient, and lower absorption coefficient in the UV-C regime (especially for wavelengths below 250 nm) compared to the HfO
₂
thin films. The fabricated YDH/SiO
₂
DBR consisting of 15 periods achieved a reflectivity higher than 99.9% at the wavelength of ~240 nm with a stopband of ~50 nm. The high reflectivity and broad stopband of YDH/SiO
₂
DBRs will enable further advancement of various photonic devices such as vertical-cavity surface-emitting lasers, resonant-cavity light-emitting diodes, and resonant-cavity photodetectors operating in the UV-C wavelength regime.