Effects of strain on ultrahigh-performance optoelectronics and growth behavior of high-quality indium tin oxide films on yttria-stabilized zirconia (001) substrates

In this study, in situ reflection high-energy electron diffraction patterns were used to observe the preparation of high-quality indium tin oxide (ITO) films on yttria-stabilized zirconia (001) substrates using laser molecular-beam epitaxy at different growth pressures and temperatures. X-ray diffraction images showed that increasing the growth temperature or decreasing the pressure diminished the out-of-plane lattice length of the film because of the increased lattice relaxation. Atomic force microscope images and scanning electron microscope showed some crack formations probably due to the release of the strain, causing an increase in the lattice length instead of decrease at the temperature range from 350 to 400 °C. High-resolution transmission electron microscopy showed that the interface between the ITO film and substrate was sharply defined, which indicates the high quality of the film. The sheet resistance of the film increased with increasing growth temperature or pressure, while the optical bandgap did not decrease monotonically because of the effects of strain in the film. Because of the strain, the ITO film initially grew as three-dimensional (3D) islands, like semiconductor quantum dots, and then changed to a quasi-two-dimensional form as the film thickness increased from 1 to 30 nm. The sheet resistance decreased rapidly as the film thickness increased from 20 to 150 nm, but the rate of decrease slowed as the film thickness increased from 150 to 500 nm. The film transmissivity was not significantly affected by the film thickness, growth temperature, or growth pressure.