Impact of flow modulation on MOCVD-grown In-rich N-polar InAlN films on sapphire

In-rich In_xAl_1-xN layers were grown on sapphire substrates with an AlN nucleation layer by metal-organic chemical vapour deposition (MOCVD). Deposition parameters were varied to achieve a high In molar fraction and optimized microstructure without InAlN phase separation. Continuous flow epitaxy (CFE) and, for the first time, flow-modulated epitaxy (FME) MOCVD growth methods were applied to In-rich InAlN. Diverse microstructural analyses were focused on the study of various crystal defects, including dislocations, significantly inclined grains, voids, and phase separation of different kinds, and were supported by electrical and optical measurements. The best structural quality was obtained by FME in 170 nm thick N-polar In_0.64Al_0.36N, demonstrating respective screw- and edge-type dislocations densities of 0.61 × 10⁹cm⁻² and 61 × 10⁹cm⁻², pits density of 2.4 × 10⁸cm⁻², surface RMS roughness of 5.3 nm, an electron density and mobility of 1.3 × 10¹⁹cm⁻³ and 37.4 cm²/Vs, respectively, and an optical band gap of 1.62 eV.