Effects of dilute alloying on the quality of ultrathin InGaN/GaN single-quantum wells

We present a theoretical investigation on the electronic properties of alloyed In_xGa_{1- x}N ultrathin single-quantum wells (SQWs) embedded in GaN matrix. The empirical tight-binding method with sp³s^- basis set, including spin-orbit interaction and nearest-neighbor two-center overlap integrals, is used to study the number of bound states, quantum confinement (QC) energy and the band-gap energy of (In_xGa_{1- x}N)_Nw/GaN SQWs versus the well composition and parameters; namely width (N_w) and depth (via valence band offset, VBO). The results show strong correlation between the bound states (number and QC energy) and the well's composition and parameters. Furthermore, the results were used to model experimental photoluminescence (PL) data of three samples containing N_w = 1, 3 and 5 monolayers (MLs), which were fabricated by A. Yoshikawa and coworkers using rate-flow plasma molecular-beam epitaxy (rf-MBE). The results have revealed that in all these three samples, the indium mole fraction would not exceed 25% and, consequently, the three wells are shown to contain at maximum 1, 2 and 3 electronic bound states, respectively. It is deduced that the maintaining of low indium content (x < 0.25) is the secret for the achievement of high structural and optical qualities of the produced samples with free of misfit dislocations.