Phonon‐Assisted Exciton Transitions in A^IIB^VI Semiconductors

Abstract

In CdS, CdSe, and CdTe investigations of both reflectivityby polarimetric methodsand transmission are made in the spectral region of energies higher than the exciton ground state. An additional structure at energies of approximate Eex + ELO is explained by indirect exciton transitions with phonon emission and compared with simple second-order perturbation theory taking into account ground exciton states only. The observed shift towards lower energies can be ascribed to the configuration interaction.In CdS, CdSe und CdTe wurden sowohl die Reflexion mit polarimetrischen Methoden als auch die Transmission fiir Enqgien groBer als der Exzitonengrundzustand untemcht.Eine zusiitzliche Struktur bei Energien von etwa Be, + ELO wird durch indirekte Exzitoneniibergiinge unter Phononenemission gedeutet und mit einer einfachen Stijrungstheorie zweiter Ordnung unter alleiniger Beriicksichtigung des Exzitonengrundzustandes verglichen. Die beobachtete Verschiebung zu niedrigeren Energien kann einer Konfigurationswechmlwirkung zugeschrieben werden.

Electroabsorption of CdS and CdSe Single Crystals in the Exciton Region

“…The characteristic features of the electroabsorption spectra taken under the same experimental conditions agree quite well for the various crystals, and the positions of the extrema coincide quantitatively within the limits of experimental error. The energies of the ground state excitons A, B, C , n = 1 found at B' = 0 are included in Table 1 and agree quite well with the corresponding data of other authors (see [29] for earlier data and references; [24]). …”

“…Such transitions have been observed in the direct absorption spectra for ZnO [28] and were also proposed in a recent paper for CdS and CdSe [29]. However, such an assignment is unlikely in view of energetic reasons, line shape arguments and the behaviour as a function of the applied field.…”

Free‐exciton absorption in bulk CdTe: temperature dependence

“…Absorption above 24000 cm -1 could not be measured, so that the FX, n = 1 (at 1.5961 eV) absorption peak is not complete. One can observe an excited state of the FX, n = 2 (at 1.6037 eV) and enhancement of absorption at the energy of FX plus LO phonon energy (at around 1.617 eV) as discussed by Dillinger et al [12]. The exciton binding energy is thus 4/3 × 7.6 = 10.1 meV, which is the well-known value.…”

Exciton-phonon resonance in the continuum absorption of bulk semiconductors

“…We begin with CdTe where accurate absorption measurements at liquid nitrogen temperature have been reported some time ago by Dillinger et al 3,4 Details on the applied numerical procedures for the Green's function and the optical response can be found in the Appendix. The parameters used are listed in Table I.…”

“…We mention absorption measurements in ionic crystals as ZnO, 1 MgO, and BeO, 2 reflectivity and transmission experiments on CdS, CdSe, and CdTe, 3,4 low temperature laser-excited photoemission of InP, 5 CdTe, Cd x Zn 1Ϫx Te and n-type CdTe:I epilayers, 6 and an ellipsometric study of Zn x Cd 1Ϫx Se 7 among the different systems and experimental configurations. In GaAs, differential transmission spectra with femtosecond time resolution 8 and high-resolution absorption spectra 9 have been reported recently.…”