Spectral Response of Solar Blind M-S-M Photodetector With InGaZnO Film Sputter Deposited in Diluted Oxygen Ambience

Indium-gallium-zinc-oxide (InGaZnO) metal-semiconductor-metal (M-S-M) photodetector has been demonstrated here, which shows enhanced spectral response in the solar blind window. It had been found that, while IGZO film (100 nm) for the MSM photodetector was sputtered in argon diluted oxygen ambience (Ar:O ₂ = 20:2 sccm) deposited film contained higher atomic percentage of gallium as compared to film sputtered in pure argon ambience. Higher Ga content (26.92– 28.14%) present in diluted O ₂ ambience sputtered film was found advantageous for stretching spectral response (SR) of detector till the solar blind window. Fabricated detector showed peak responsivity of 1.12 A/W at 255 nm and at 8V when as-deposited diluted O ₂ sputtered film in it received two consecutive anneals beginning with ozone (O ₃ ) at 90°C for 30 minutes followed by a 300°C thermal anneal for 1 hour in nitrogen (N ₂ ). Substantial improvement in responsivity as found in solar blind window has been attributed to enhanced absorption by IGZO in deep UV band separately characterized using absorption spectra of diluted O ₂ sputtered and post deposition annealed IGZO films. Enhanced UV-absorption was resulted from structural relaxation of lattice prompted by higher Ga content present in as-deposited films, which reduces ionization energy of deep lying neutral oxygen vacancy states within the IGZO bandgap thereby increases free carrier density impacting extinction coefficient.