The design of fluoride-based optical devices for deep ultraviolet applications is discussed. Variations in the band-gap energy and band structure with respect to composition are investigated for ${\mathrm{Li}}_{(1-x)}{\mathrm{K}}_x{\mathrm{Ba}}_{(1-y)}{\mathrm{Mg}}_y{\mathrm{F}}_3$ perovskites. The band-gap energy, lattice constant, and band structure of perovskitelike fluorides are estimated based on ab initio calculations within the local-density approximation. The lattice-matched double heterostructure with direct band-gap compounds (${\mathrm{Li}}_{(1-x)}{\mathrm{K}}_x{\mathrm{Ba}}_{(1-y)}{\mathrm{Mg}}_y{\mathrm{F}}_3$ on either $\mathrm{Li}\mathrm{Ba}{\mathrm{F}}_3$ or $\mathrm{K}\mathrm{Mg}{\mathrm{F}}_3$ substrates) is promising for fabrication.

Vacuum ultraviolet radiation (VUV, from 100 nm to 200 nm wavelength) is indispensable in many applications, but its detection is still challenging. We report the development of a VUV photoconductive detector, based on titanium dioxide (TiO₂) nanoparticle thin films. The effect of crystallinity, optical quality, and crystallite size due to film thickness (80 nm, 500 nm, 1000 nm) and type of substrate (silicon Si, quartz SiO₂, soda lime glass SLG) was investigated to explore ways of enhancing the photoconductivity of the detector. The TiO₂ film deposited on SiO₂ substrate with a film thickness of 80 nm exhibited the best photoconductivity, with a photocurrent of 5.35 milli-Amperes and a photosensitivity of 99.99% for a bias voltage of 70 V. The wavelength response of the detector can be adjusted by changing the thickness of the film as the cut-off shifts to a longer wavelength, as the film becomes thicker. The response time of the TiO₂ detector is about 5.8 μs and is comparable to the 5.4 μs response time of a diamond UV sensor. The development of the TiO₂ nanoparticle thin film detector is expected to contribute to the enhancement of the use of VUV radiation in an increasing number of important technological and scientific applications.

We report the development of filterless deep ultraviolet photoconductive detectors using cerium fluoride (CeF₃) thin films fabricated by pulsed laser deposition (PLD). By varying the PLD laser power during thin film growth, we observed that CeF₃ breaks down to CeF₂ at PLD laser powers greater than 100 mW. This consequently leads to the formation of fluorine defects that effectively narrowed the optical bandgap of the thin films, resulting in the decreased resistivity of the photoconductive detector. Under ultraviolet irradiation, the detector using a thin film grown at 5 mW PLD laser power exhibited close to four orders of magnitude increase in photocurrent compared to the dark current. The spectral response of the photoconductive detectors can be tuned from 300 nm to 400 nm when PLD laser powers ranging from 5 mW to 400 mW are used to fabricate the thin films. The filterless nature of the detectors simplifies their production, and their tunability can extend their use to a wider range of applications.

A significant enhancement of THz radiation from an InAs clean (100) surface is observed with irradiation of femtosecond laser pulses at 50 K. Due to the surface cleaning and cooling temperature, the THz-radiation intensity from the InAs clean (100) surface at 50 K becomes to 10 times larger than that from an uncleaned surface at room temperature.