Recently, photodetector based on semiconductor-insulator-semiconductor (SIS) heterojunction structure which contains indium zinc oxide (IZO) as the transparent conductive oxide (TCO) layer was reported. In that work, IZO layer was deposited by pulsed laser deposition which is impractical to the large-area device production. Moreover, the IZO contains indium which becomes a scarce element due to the vast demand in solar cell and display industries in recent years. In order to overcome these difficulties, aluminum zinc oxide (AZO) was adopted to replace IZO as the TCO layer and the feasibility of AZO/SiO_x/n-Si SIS structure to photodetection was investigated.

The SIS structure was prepared firstly by growing SiO_x layer with appropriate thickness (~1.8 nm) on n-type Si wafer substrate by dry thermal oxidation method. Radio-frequency sputtering was then adopted to deposit a 200-nm thick AZO layer on SiO_x/Si substrate. Afterward, the 100-nm thick aluminum layers were deposited by e-beam evaporation to form the bottom electrodes on the backside of Si substrates and the top finger electrodes on AZO layer, respectively, to complete the SIS photodetector preparation.

Without applying external bias, the sample with quick photo-response time less than 10 msec and photoresponse (R) of 0.17, 0.67 and 0.22 AW^-1separately under the 365-nm, 650-nm and 940-nm illuminations were achieved. The lower R value at short-wavelength illumination was attributed to the absorption of AZO layer since the photon energy of incident light is close to the absorption edge of AZO. The sample was further annealed at 300°C for 1 hr in air ambient and the improvement of R values, 0.27, 1.60 and 0.67 AW^-1 under the 365-nm, 650-nm and 940-nm illuminations, was observed. The improvement of R values of the device was ascribed to the reduction of interface trap density (D_it) at the AZO/SiO_x and SiO_x/n-Si interfaces as revealed by the capacitance-voltage measurement. The annealing treatment reduced the D_it from 1.63×10¹² to 2.80×10¹¹ eV^-1cm^-2, which efficiently alleviated the carrier capture at interfaces and improved the photodetection properties of the sample.

Keywords: Photodetector; Aluminum zinc oxide; Semiconductor-insulator-semiconductor heterojunction; interface trap density.