Surface potential modification of molecular beam epitaxially grown SrTiO$_{3-\delta}$/Si(001) measured by Kelvin Force Probe Microscopy

SrTiO$_{3}$ (STO) films have been grown by molecular beam epitaxy on p-Si(001), n-Si(001), and STO(001) substrates. The STO/Si films were of high crystalline quality as determined by x-ray diffraction (XRD) and TEM and ranged in thickness from 3.6 to 60 nm as measured by x-ray reflectivity (XRR). The partial pressure of oxygen (O$_{2})$ was varied during growth to induce oxygen vacancies within the STO structure. Through additional XRD and magnetotransport studies, we estimate that for the lowest O$_{2}$ pressure the oxygen deficiency is $\delta =$0.02. The surface potential of the films was modified through the use of a conducting atomic force microscopy (AFM) tip by scanning regions of the STO surface in contact mode with a DC bias on the tip (referred to as `writing'). Regions were written with either positive or negative voltage and then analyzed by Kelvin Force Probe Microscopy (KFPM). Following this writing mode, KFPM revealed a retained surface potential of the same polarity used in writing. The ability of the films to be written and read through this method depended on the growth O$_{2}$ partial pressure with higher O$_{2}$ pressures demonstrating weaker surface potential modification. The results agree with other studies regarding the drift and diffusion of charged O$_{2}$ vacancies in STO.