A Model for Surface Space Charge Mediated Ultraviolet Photoresponse in MgZnO Thin Films and Its Experimental Verification

We propose a model based on the evolution of electron and surface charge density to describe the ultraviolet photoresponse in MgZnO thin films. The MgZnO surface contains a high density of surface bound states for electrons due to chemisorption of oxygen molecules, resulting in formation of a surface depletion region. We take into account the change in both conducting volume and electron density in the nondepleted part of the MgZnO thin films upon UV illumination to model temporal variation of photocurrent. We have deposited a set of MgZnO thin films on Al electrodes by pulsed laser deposition at different oxygen pressures to verify the model. With increasing oxygen pressure, dark current, peak responsivity, and response time decreased while the ON–OFF ratio and UV to visible rejection ratio increased, implying different levels of oxygen chemisorption. The proposed model has been successfully used to simulate the temporal decay of the photocurrent in the deposited devices.