Evaluation of thermal and growth stresses in heteroepitaxial AlN thin films formed on (0 0 0 1) sapphire by pulsed laser ablation

Abstract

Structural properties of heteroepitaxial AlN thin films deposited by pulsed laser ablation on (0 0 0 1) sapphire without and with simultaneous irradiation of the growing thin film surface by 500 eV nitrogen ions are characterized using X-ray diffraction. Temperature dependencies of residual stresses, unstressed lattice parameters and thermal expansion coefficients are evaluated in the range of 298–873 K. Though the results document significant differences in structural parameters between thin films formed with and without the ion beam irradiation, the temperature behavior of stresses in the thin films is comparable. The heating of the structures up to 873 K induces a reversible stress change of about 545 MPa in the films possessing distinctly different room temperature stress values. The experimental measurements allow to quantify the contributions of growth and thermal stresses to the total stress in both types of films. The temperature dependencies of stresses in the thin films are consistent with the model of thermal stresses based on the mismatch of the thermal expansion coefficients of AlN and sapphire.