Highly anisotropic dispersion of surface acoustic waves in M-plane GaN layers grown on γ-LiAlO2(100) -: art. no. 115317

The characteristics of surface acoustic waves (SAW's) in M-plane GaN and AlN layers grown on gamma-LiAlO2(100) are investigated. The SAW velocities in the (100) plane of bulk gamma-LiAlO2 are virtually identical along the [010] and [001] directions and are significantly larger than those in the M-plane bulk GaN. Despite these velocity relations, the SAW velocity in GaN/gamma-LiAlO2 heterostructures increases steadily along the GaN[11 (2) over bar0] direction with increasing the SAW wavelength, whereas it decreases along the GaN [0001] direction. A guided Rayleigh mode is observed solely for the propagation along the GaN[11 (2) over bar0] direction. These experimental results are compared with numerical simulations. Velocity bowing is indicated to govern the dispersion in the heterostructures.