Stress Engineering and Optimization of Thick Garnet Crystal Films Grown by Pulsed Laser Deposition

We present here results indicating that stress in films grown by pulsed laser deposition (PLD) may be engineered simply by altering the growth parameters of substrate temperature and laser fluence to balance tensile and compressive stresses. Compositional and structural analysis of Gd3Ga5O12 (GGG) films grown on Y3Al5O12 (YAG) substrates, using three different PLD setups and two different ablating lasers, reveals the effects of different growth parameters on residual stress. Some stress reduction strategies were investigated, including slower heating and cooling ramp rate, and amorphous buffer layers, but changing the growth parameters of substrate temperature and laser fluence was found to have a more significant effect. To characterize the evolution of film stress as thickness increases for different laser fluences, three films were grown in stages to allow substrate curvature measurements and X-ray diffraction analysis to be performed every time the thickness had doubled (from 1 to 16 μm in thickness). The results from these experiments reveal a compressive stress that relaxes with thickness, thought to be due to lattice mismatch, and leads to the conclusion that stress in PLD grown films of GGG on YAG is a balance between lattice mismatch, thermal expansion mismatch, and ion-bombardment.