Dependence of Texture Tilt and Excitation Efficiency of Shear Waves for ZnO Films on Working Gas Pressure in a DC Magnetron System

Resumo

Dependence of the texture tilt and excitation efficiency of shear waves on the working gas pressure in an interval of 0.14–0.74 mTorr that corresponds to the transition from collisionless to almost diffusion deposition is studied for the ZnO films with a thickness of about 0.45–1.2 μm that are synthesized in a planar dc magnetron system. It is shown that an increase in the pressure from about 0.14–0.24 to 0.74 mTorr causes a decrease in the tilt angle of the column texture from ~25°–27° to ~7° and a decrease in the efficiency of acoustic excitation. Films that are synthesized at pressures of ~0.14–0.24 mTorr close to the transition from the Townsend to glow discharge exhibit the highest excitation efficiency of shear waves. For such films, the insertion loss reaches a minimum level at thicknesses of 0.45–0.75 μm and the number of echo pulses amounts to 20–40, so that the reflected sound can be observed with a delay of up to 80 μs at a length of an acoustic guiding crystal of 10 mm.