Structural and optical characterisation of thick InN epilayers grown with a single or two step growth process on GaN(0001)

Abstract

High resolution transmission electron microscopy (HRTEM), Raman spectroscopy and temperature dependent photoluminescence (PL) are employed to compare the structural and optical properties of compact InN films grown by molecular beam epitaxy (MBE) on GaN/Al 2 O 3 (0001) with a single-step (S) or a two-step (T) growth process. The S-type film was grown at 300 °C, whilst the T-type film was nucleated at the same temperature and overgrown at 410 °C. The T-type film exhibits better structural and optical properties as indicated by a sharper InN/GaN interface, the lower threading dislocations density, sharper Raman peaks and higher intensity PL peaks. Quantitative comparison of the red-shifted Raman E 2 2 peak and the lattice constants of S and T samples suggests that the InN epilayers are under different values of stress due to thermal reasons and point defects present in them. The PL emission peak difference of 32 meV between S and T provides further evidence of the unequal residual strain present in InN.