Band parameters of CdS and CdSe single crystals determined from optical exciton spectra

Abstract

Abstract An investigation is made of the energy spectra of A and B excitons in CdS by measuring the transmission and reflectivity of very thin highly perfect crystals at 1.8 K. The excited states of both series follow hydrogen‐like series in a good approximation yielding different Rydberg's R = (28 ± 0.4) and R = (31.3 ± 0.4) meV, whereas the ground states are shifted in opposite direction with respect to the series, δ E = −2.2, δ E = +0.5 meV, resulting in exciton binding energies E = 30.2 and E = 30.8 meV, which are different from the corresponding Rydberg energies. This effect could not be attributed to a single perturbation acting on the ground state in different ways. Moreover, oscillator strengths are determined. A discussion is given in terms of the quasi‐cubic model. For CdSe, the exciton‐LO‐phonon interaction is investigated using a line‐shape analysis of the absorption lines at different temperatures. Analogous to other II–VI compounds, at higher temperatures ( T > 77 K) this interaction is the dominate one for the exciton absorption spectra.