Achieving sensitive and stable indium oxide thin films for gamma radiation monitoring

Abstract

Indium oxide thin films of thickness 600 nm prepared by thermal evaporation in vacuum were annealed at different temperatures from 350 to 550 °C. The impact of the post-deposition thermal annealing on the structural evolution of the films, including the growth of grains, was investigated by XRD and SEM. The annealed films were also evaluated by X-ray photoelectron and photoluminescence spectroscopy. The gamma radiation dose dependences of the optical energy band gap for the as-deposited and annealed thin films were investigated using transmittance measurements. The band gap decreases with increase of dose for the as-deposited and thermally treated films up to certain level and then increases. Coplanar devices were fabricated using the as-deposited films and films annealed at different temperatures. After exposing them to different gamma radiation doses, DC conductivity measurements were carried out. The gamma radiation sensing property of the indium oxide thin films annealed at 400 °C exhibits the highest sensitivity in comparison to the as-deposited films and films annealed at other temperatures. The annealing at temperatures higher or lower than 400 °C causes an increase of electrical resistivity and decrease in sensitivity of the films. Also, the stability of the sensor devices was studied for about 8 months. The results showed that the sensors made of the as-deposited films were stable for about 2 months and lost about 52% of their sensitivity in about 8 months whereas the sensors made out of the films annealed at 400 °C were stable for about 4 months and lost about 26% of their sensitivity in about 8 months. This study presents a key idea of using the post-deposition thermal annealing to achieve highly sensitive and stable In2O3 film as gamma radiation sensor.