Facilitated extrinsic majority carrier depletion and photogenerated exciton dissociation in an annealing-free ZnO:C photodetector

Abstract

Applications of ZnO in photodetectors are limited by the great quantity of extrinsic majority carriers due to structural defects and difficult exciton dissociation due to the large exciton binding energy; these generally lead to a higher dark current (I_d) and lower light current (I_l), severely degrading the responsivity and detectivity. C dots are incorporated into an annealing-free ZnO layer to innovatively construct a local built-in electric field (E_bi) using the difference in the work functions; this simultaneously overcomes the drawbacks of the pristine ZnO photosensitive layer. In dark, the extrinsic majority carrier of ZnO is depleted around the incorporated C dots due to the self-depleting effect; thus, the I_d decreases. Under UV illumination, the photogenerated exciton driven by the local E_bi is easily dissociated into a free charge carrier, contributing to the improved I_l. This study paves a universal way to effectively improve the detection characteristics of photoconductive devices by incorporating the local E_bi.