Influence of grain size on local work function and optoelectronic properties of n-ZTO/p-Si heterostructures

In this work, we investigate on tunability of the local work function, morphological, structural, electrical, and optical properties of ZTO (zinc tin oxide) thin films. Using Kelvin probe force microscopy, we demonstrate that local work function of ZTO films can be tuned from 5.04 to 4.94 eV by varying the film thickness from 60 to 240 nm. X-ray diffraction studies reveal the amorphous nature of ZTO films, whereas AFM measurements confirm their granular nature. It is observed that the average grain size increases (from 24 to 58 nm) with increasing film thickness. In addition, a systematic red shift in the band gap as well as a decrease in the resistivity takes place with increasing thickness. Moreover, current-voltage characteristics show a systematic reduction in the turn-on potential and an enhancement in the leakage current with increasing ZTO film thickness. Above observations are explained in the framework of ZTO thickness-dependent variation in the grain size. This study will be of importance to make a transparent conductive oxide-based electrode in photovoltaic applications and ZTO-based optoelectronic devices.