Fast switching response of Na-doped CZTS photodetector from visible to NIR range

It is important to study the photoconductivity to understand the optoelectronic properties of semiconductor thin films. Here, we report the effect of Na doping on the photoconductivity properties of CZTS (Cu2ZnSnS4) in the visible and NIR region. CZTS thin films were deposited on quartz and silicon dioxide substrates using stacked layer reactive sputtering and annealing. The photoconductivity of undoped CZTS and Na-doped CZTS in visible region (excitation wavelength - 532 nm) and in the NIR region (excitation wavelength - 1064 nm) were studied. At a bias voltage of 150 mV, response rise time for undoped CZTS in the visible region was 1.02 s which decreased to 391 ms for Na-doped CZTS. The rise time in NIR region decreased from 245 ms (for undoped CZTS) to 1.06 ms (for Na-doped CZTS). The decay time for undoped sample (in the visible region) was 1.20 s, which decreased to 221 ms (for Na-doped CZTS). In the NIR region, the decay time decreased from 342 ms (undoped CZTS) to 29.80 ms (Na-doped CZTS). A large increase in the photocurrent response (from 6.5 to 2320 times in the visible region and from 12.6 to 3384 times in the NIR region) in the CZTS upon Na doping was observed. Thus, switching in the NIR region is improved drastically upon Na doping in CZTS. Therefore, it can be concluded that Na-doped CZTS can be utilized as NIR photodetector.