Experiment and Theoretical Calculation of the Surface Space Charge Region Effect on Photocurrent Generation of SnO2 Bilayer Photodiode Devices

In this work, a SnO2 bilayers photodiode device is designed, which consists of a thin SnO2 photocurrent generation layer and a SnO2 thick layer on the glass substrate. The SnO2 photocurrent generation layer with high oxygen vacancy concentration is intentionally prepared. With annealing in oxygen ambient, an electrical potential would be built in the surface space charge region in the thin SnO2 photocurrent generation layer, which would drive the photocarriers down to and flow in the photocarrier transportation layer, i.e., the high-mobility SnO2 thick film on the glass substrate. The designed SnO2 bilayers photodiode device could enhance photocurrent generation and resolution for the SnO2-based UV-photodetectors. It is concluded that the width of surface space charge region is the key factor for the enhancement of lifetime of photocarriers and photocurrent generation ofthe current SnO2 bilayers photodiode. Based on the present experimental results, the width of the surface space charge region is expected to be nearly or less than 3 nm. Moreover, in this work, a theoretical model is developed to calculate the width ofthe surface space charge region. The calculated width of the surface space charge region (3.26 nm) is close enough to support the present experimental observation.