Sol-gel prepared amorphous Ta2O5 thin film for application in high LIDT antireflection coating and UV photodetection

Abstract

In this report, a sol–gel method has been developed using tantalum ethoxide to produce homogenous thin films of amorphous Ta2O5 for application in optical coating for high power laser as well as photodetection in the UV range. Morphology, stoichiometry, optical properties, short range atomic structure and valence band have been investigated at various annealing temperature up to 500 °C. A large valence band onset of 3.5 ± 0.20 eV has been measured for the film annealed at 500 °C, ensuring hole blockage through the film and electron selective transport. Extended X-ray absorption fine structure (EXAFS) study has revealed the Ta–O bond distance to be 1.85 Å for as-deposited film, which increased with annealing and approached the crystallographic value. The sol-gel prepared Ta2O5 film has been used as antireflection (AR) coating on silicon and fused silica (FS) substrates. 99.4% transmission with a LIDT of 20 J/cm2 @6 ns at 1064 nm is obtained for Ta2O5/SiO2 AR coatings on FS. Using these sol-gel films, Ta2O5/Si vertical heterojunction photodetectors have been fabricated, which exhibited a responsivity of 560 mA/W, external quantum efficiency of 213%, and specific detectivity ∼1 × 1012 Jones at −1 V bias voltage and 325 nm illumination wavelength.