Effects of growth temperature on structural and electrical properties of in-rich InAlN–GaN heterostructures by radio-frequency metal–organic molecular beam epitaxy

Abstract

In-rich InAlN is a promising nitride semiconductor alloy for high-efficiency solar cells and wide-range light-emitting diodes due to its tunable bandgap from 0.7 to 6.2 eV. However, incomplete characterization has led to inconsistent fundamental properties in some studies. The aim of this study was to comprehensively investigate the structural, optical, and electrical properties of In-rich InAlN films grown on GaN/Al2O3 templates by RF-MOMBE at various temperatures. The methodology involved state-of-the-art metrology techniques, such as high-resolution x-ray diffraction (HRXRD), scanning electron microscopy (FE-SEM), Hall effect measurements, and transmission electron microscopy (TEM). The results showed that all InxAl1-xN films were epitaxially grown on the GaN/Al2O3 template, with the indium composition (x) decreasing with increasing growth temperature. Furthermore, phase separation of the In-rich InAlN films occurred at high growth temperatures(>550 °C), resulting in a relatively smooth surface. The optical absorption method measured the band-gap of the InxAl1-xN films, which ranged from 1.7 to 1.9 eV for x values between 0.77 and 0.91. The mobility and carrier concentrations of all In-rich InAlN films were measured at ∼60−277 cm2 V−1-s−1 and 2–7 × 1019 cm3 in the growth temperature of range 450 °C–610 °C, respectively. In conclusion, our comprehensive characterization using advanced metrology methods provides valuable insights into the properties of In-rich InAlN films, which can inform future optimization of these materials for various applications.