Development of Sn Oxide Hetero-Junction Band Alignment via Oxygen Plasma Treatment Suitable for Photo-Sensing Applications

We report on results referring to the growth and characterization of Sn-oxide-semiconductor thin films (SnO2, SnO and intermediate Sn3O4) on silicon substrates forming Type II heterojunction band alignment. The samples were produced by a two-step procedure: (a) growth of a metallic Sn layer by RF magnetron sputtering deposition followed by (b) post-growth treatment of the Sn films with oxygen plasma etching for the formation of the oxides in various time steps. Various annealing steps were considered. The structural and chemical properties of the prepared thin films were determined by means of X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS). The results demonstrated the presence of SnO2 and SnO in a tetragonal structure and the intermediate Sn3O4 in a triclinic structure. The electric properties of thin films were investigated with four-probe I–V characteristics under various conditions. The evaluation of their photo-sensing properties was performed by means of photocurrent J–t curves using a solar simulator. We found that the sample with equal concentrations of SnO2 and SnO exhibited superior responsivity and detectivity values as well as a responsivity of 12.5 A/W and detectivity of 1.1 × 1010 Jones for V = 0 under yellow light illumination and an intensity of 2 mW/cm2. These excellent values, in combination with the low-cost manufacturing, indicate that the method is promising for future applications.