A CuInSe2 (CIS) bulk single crystal grown by the directional freezing method from the melt at 1250°C shows superior crystal quality, as evidenced by its (p-type) electrical properties. Photoluminescence at 1.5 K shows a strong and well resolved spectrum with fine structures never before observed from this compound. Free exciton emission exhibits a doublet structure which can either be described as a splitting due to the uniaxial crystal field or as a polariton. The energy gap of the CIS semiconductor as determined from the temperature dependence of the free exciton line is 1.058 eV. Two moderate free-to-bound transitions are assigned to VCu and CuIn acceptors. A weak PL peak corresponding to a deep level is interpreted as arising from the Sei acceptor. Strong phonon replicas are also observed for the first time in a CIS bulk single crystal. The phonon wavelength of 218–237 cm-1 is in good agreement with the reported Raman result of 233 cm-1 for the LO phonon.
Many-body effects have been optically investigated for modulation-doped quantum wells at high acceptor densities. The observed band-gap shrinkage, up to Ϸ20 meV, is consistent with calculations based on the Hartree and random-phase approximations including the finite well width effect. A recombination near the Fermi edge with light-hole character is strikingly enhanced at high acceptor densities. An interpretation based on carrier-carrier interaction is proposed. Finally, the exciton is found to be quenched for hole densities higher than Ϸ2ϫ10 12 cm Ϫ2 .
An experimental evidence of Auger-like excitation processes in InAs/GaAs quantum dots is demonstrated. Photoluminescence spectra of resonantly excited dots exhibit a rich satellite structure below the ground-state emission band. The energy position and the intensity distribution of the satellites are analyzed and an interpretation of the satellites as due to shakeup processes of the interacting carriers in the higher quantum dot states is suggested. The potential of quantum dot (QD) structures for optoelectronic device applications has been frequently questioned due to the suppression of the carrier relaxation rate in zero-dimensional systems [1]. The discrete nature of the density-of-states dispersion in QDs prevents the effective carrier relaxation unless the electron level spacing is smaller than a few meV to favour the LA-phonon scattering or equals the typical LO-phonon energies. This effect, referred to as the "phonon bottleneck" , should result in a considerable reduction of the luminescence efficiency and should also constitute a significant limitation of the performance for QD-based devices. The role of phonons in the relaxation of the carriers in self-assembled InGaAs/GaAs QDs have been studied by resonant excited photoluminescence (PL) and radiative lifetime measurements of excited states [2 and 3].The phonon bottleneck problem could be removed or at least reduced if the carrier transfer to lower states could occur via Auger processes [4, 5 and 6]. Experimentally, Auger processes can be demonstrated by means of satellite spectroscopy. In this case, the photo-excited electron-hole pair interacts with other carriers and as result an excitation of the additional carriers in higher states takes place. These shake-up processes can be monitored in the PL spectra as satellites which are red-shifted relatively the principal electron-hole pair recombination. The satellite spectroscopy has been a widely used method to study Auger-like processes in semiconductor quantum wells (QWs), but the final state for the interacting carriers varies for different shake-up processes, e.g., a higher Landau level for an electron gas or a negatively charged exciton in a magnetic field [7 and 8] and a higher subband for a two-particle transition [9]. The prerequisite
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.