Evidence for fractional filling in ultrathin GaInN/GaN multiple-quantum wells

The (Ga _{1 - x}In _xN) _Nw/GaN single- and multiple-quantum wells (SQWs, MQWs) are theoretically investigated using the sp ³s* tight-binding (TB) method, with inclusion of spin-orbit coupling. Because of the huge mismatch in both the lattice constant and the energy gap between the constituent materials, two trends are shown to clearly put on display: (i) the existence of two types of confinement characters inside the deep wells of GaInN. The bound states at the bottom of the well are found to be singlets and to follow the power-law quantum confinement (QC) character, similar to the case of a single particle in a quantum box. Whereas the bound states at the top of the well follow the exponential localization as being relatively weaker in their QC characters. (ii) In the limit of ultrathin quantum wells (QWs), the indium content is found to be restricted to remain low if coherent growth is aimed. This restriction is found to be natural as a compromise to maintain the growth free of misfit dislocations. For instance, in case of 1-ML thick QWs, the indium content is found to be as low as ranging in the interval 0.15 < x < 0.25. Such restriction is corroborated by recent experimental evidence. The favorable modeling of our theoretical results to recent photoluminescence data further support our claims.