MBE Grown In _x Ga_1−x N Thin Films with Bright Visible Emission Centered at 550 nm

Abstract

The In _x Ga_1−x N thin films with indium content of x = 14–18 at.% were successfully grown by using molecular beam epitaxy (MBE) at high growth temperatures from 650°C to 800°C. In situ reflection high-energy electron diffraction (RHEED) of the In _x Ga_1−x N films confirmed the Stranski–Krastanov growth mode. X-ray diffraction (XRD) of the films confirmed their highly crystalline nature having c-axis orientation with a small fraction of secondary InN phase admixture. High-resolution cross-sectional scanning electron microscopy images showed two-dimensional epilayers growth with thickness of about ∼260 nm. The high growth temperature of In _x Ga_1−x N epilayers is found to be favorable to facilitate more GaN phase than InN phase. All the fundamental electronic states of In, Ga, and N were identified by x-ray photoelectron spectroscopy (XPS) and the indium composition has been calculated from the obtained XPS spectra with CASAXPS software. The composition calculations from XRD, XPS and photoluminescence closely match each other. The biaxial strain has been calculated and found to be increasing with the In content. Growing In _x Ga_1−x N at high temperatures resulted in the reduction in stress/strain which affects the radiative electron–hole pair recombination. The In _x Ga_1−x N film with lesser strain showed a brighter and stronger green emission than films with the larger built-in strain. A weak S-shaped near band edge emission profile confirms the relatively homogeneous distribution of indium.