Investigation of electromechanical distortions in gallium nitride by reflectance anisotropy spectroscopy

Real time reflectance spectroscopy has been used to investigate the extent and development of dielectric anisotropy during chemical beam epitaxy of gallium nitride on a GaAs(001) substrate using a low temperature aluminium nitride buffer layer. Reflection anisotropy between the [1̄10] and [110] directions indicates a strong cubic symmetry with bulk anisotropic strains of the order of 0.001. Post-growth reflectance measurements have been made to investigate electromechanical distortions in the gallium nitride epilayer when an electric field was applied in the [001] direction. The d14 piezoelectric modulus of cubic gallium nitride is estimated to be 1.95pmV−1. Reflectance anisotropy spectroscopy is shown to be a sensitive method for the measurement of electromechanical effects in thin films, and in particular a novel method for investigating thin film semiconductor piezoelectric materials.