Origin of additional spectral features in modulated reflectance spectra of 2-dimensional semiconductor systems

Abstract

High resolution photoreflectance (PR) spectroscopy study on a single GaAs/AlGaAs quantum well representing a two-dimensional (2D) system, shows additional distinct spectral features on the high energy side of the first confined heavy-hole and light-hole exciton transitions. The PR experiments involved a special dual detection technique which significantly improved the measurement sensitivity. Photoluminescence excitation spectroscopy data on the sample showed broadened step-like features around these energies. A detailed lineshape analysis, including first principles simulations, was performed to understand the origins of these additional PR spectral features. They are shown to arise primarily from inhomogeneously broadened first excited state transition of the excitons, rather than from a change in the joint density of states at the exciton continuum edge. The analysis suggests that such features are more likely in the case of 2D excitons as compared to 3D excitons in bulk material. Apart from its significance for post-growth characterization, identification of these additional PR features enables direct estimation of the exciton binding energy. V

Band Gap Tuning of CH3NH3Pb(Br1–xClx)3 Hybrid Perovskite for Blue Electroluminescence

“…We have calculated the band gap for the different alloy samples by evaluating the Sommerfeld factor for excitons in a 3D system. 27,28 The absorption coefficient (α(ε)) is given by the following expression…”

“…ε is a dimensionless quantity related to photon energy E by ε = ( E – E g )/ R y *, with E g being the effective bandgap. We have calculated the band gap for the different alloy samples by evaluating the Sommerfeld factor for excitons in a 3D system. , …”

Recent Advances in Metal Halide‐Based Perovskite Light‐Emitting Diodes

“…As n increases, the energies of the exciton lines converge and at the band edge the absorption coefficient becomes large and becomes large and finite instead of being zero below the excitonic peak wavelength. A more accurate method of determining the perovskite bandgap energies using the Elliot theory was applied by Kumawat et al . and other researchers; using this method, bandgap energies were found to vary from 2.42 (in case of MAPbBr 3 ) to 3.16 eV (in case of MAPbCl 3 ) as the concentration of the Cl ion ( x ) was varied from 0 to 1 in MAPb(Br 1− x Cl x ) 3 …”