Dependence of the structural, the electrical, and the optical properties on the Ar/O2 flow-rate ratios for SnO2 thin films grown on p-InP (1 0 0) substrates at low temperature

SnO2 thin films on p-InP (1 0 0) substrates were grown at various Ar/O2 flow-rate ratio by using radio-frequency magnetron sputtering at low temperature. Atomic force microscopy images showed that the SnO2 films grown on the InP (1 0 0) substrates at an Ar/O2 flow rate of 0.667 and at a temperature of 250°C had the best surface morphologies among the several samples, and X-ray diffraction and transmission electron microscopy (TEM) measurements showed that the SnO2 thin films grown on the InP (1 0 0) substrates were polycrystalline layers with local epitaxy regions. An electron diffraction pattern and TEM measurements showed that the SnO2/p-InP heterostructures had no significant intermixing problems at the heterointerfaces. The capacitance–voltage measurements at room temperature showed that the majority carrier type of the nominally undoped SnO2 film was n-type and that the carrier concentration of the nominally undoped SnO2 film grown at an Ar/O2 flow rate of 0.667 had a minimum value. Photoluminescence spectra showed that peaks corresponding to the donor–acceptor pair transitions were dominant and that the peak positions changed significantly depending on the Ar/O2 flow rate. These results indicate that the SnO2 epitaxial films grown on p-InP (1 0 0) substrates at low temperature hold promise for potential electronic devices based on InP substrates, such as superior gas sensors, and high-efficiency solar cells.