Thin-film induced stress in GaAs ridge-waveguide structures integrated with sputter-deposited ZnO films

ZnO films were deposited on a GaAs ridge structure using radio-frequency (rf)-magnetron sputtering. A SiO2 thin buffer layer was introduced to alleviate a thermal mismatching problem between the ZnO film and the GaAs substrate. Deposition parameters such as rf power, distance, and gas composition/pressure were optimized to obtain highly c-axis oriented and highly resistive ZnO films. Postdeposition anneal treatment at 430 °C for 5–10 min was found to enhance c-axis orientation of the ZnO films dramatically and to reduce intrinsic stress significantly. Stress on the cleaved facet of the waveguide was imaged with a spatially resolved and polarization-resolved photoluminescence technique. The results showed that the GaAs mesa is stressed up to 1×109 dyn/cm2 (10−3 strain) due to residual stress from the ZnO/SiO2/GaAs structure.