High-resolution nonlinear optical spectroscopy of InGaN quantum dots in GaN nanowires

Abstract

High resolution coherent nonlinear optical spectroscopy of an ensemble of red-emitting InGaN quantum dots in GaN nanowires is reported. The data show a pronounced atom-like interaction between resonant laser fields and quantum dot excitons at low temperature that is difficult to observe in the linear absorption spectrum due to inhomogeneous broadening from indium fluctuation effects. We find that the nonlinear signal persists strongly at room temperature. The robust atom-like room temperature response indicates the possibility that this material could serve as the platform for proposed excitonic based applications without the need of cryogenics.

Efficient coupling of disorder states to excitons in an InGaN nanostructure

“…1b) shows a series of resonances that are peaked in amplitude around 2.05 eV and slowly roll off as a function of energy. Similar results from previous studies have been observed [20,26], where the resonant structures in the degenerate nonlinear absorption spectrum were assigned to exciton transitions. Here we attribute the resonances to quantum-confined exciton states from different sized DINWs within the ensemble, an assignment that will be further validated shortly.…”

“…A negative dT/T offset has been observed in previous nonlinear spectroscopy studies of self-assembled DINW samples [20]. The origin of the negative offset, which can be observed in degenerate CPP spectra as well, is still under investigation, however it may be an effect related to bandgap renormalization or screening [20,28,29]. A zoomed-in view of the non-degenerate CPP spectrum for a fixed probe near 1.95 eV is shown in Fig.…”

“…The measurement is repeated for several different fixed probe energies and the same qualitative behavior is observed in each case, however the magnitude of the negative dT/T background signal generally increases as a function of fixed probe energy. A negative dT/T offset has been observed in previous nonlinear spectroscopy studies of self-assembled DINW samples [20]. The origin of the negative offset, which can be observed in degenerate CPP spectra as well, is still under investigation, however it may be an effect related to bandgap renormalization or screening [20,28,29].…”

“…Emission in planar quantum wells is instead provided by radiative recombination of electron-hole pairs trapped by localized disorder states that are small enough to avoid the defect sites [17]. Recent results have confirmed that large densities of disorder states can also exist in DINW systems [20], although, as noted above, the emission from DINWs has been shown to be dominated by radiative recombination from quantum confined exciton states rather than localized disorder states.…”