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.