Exciton states in wurtzite InGaN strained coupled quantum dots: Effects of piezoelectricity and spontaneous polarization

Abstract

Within the framework of the effective-mass approximation, exciton states confined in wurtzite InxGa1−xN∕GaN strained coupled quantum dots (QDs) are investigated by means of a variational approach, including three-dimensional confinement of the electrons and holes in the QDs and strong built-in electric field effects caused by the piezoelectricity and spontaneous polarization. The relationship between exciton states and structural parameters of coupled QDs is studied in detail. We find that the strong built-in electric field in the InxGa1−xN∕GaN strained coupled QDs gives rise to a marked reduction of the effective band gap of InxGa1−xN QDs and leads to a remarkable increasing of the emission wavelengths. Both the sizes and alloy fluctuations of QDs have a significant influence on the exciton states and interband optical transitions in coupled QDs. Moreover, the barrier thickness between the two coupled InxGa1−xN QDs has a considerable influence on the exciton states and optical properties. When the barrier thickness is increased, the exciton binding energy is reduced, the emission wavelength is increased, and the electron-hole recombination rate is obviously reduced. Our theoretical results are in good agreement with the experimental measurements.