Study of the radiative mechanism of the 1.471-eV luminescent band in polycrystalline CdTe films

Abstract

The PL spectrum of CdTe at low temperatures usually shows a luminescent band in the low energy side at 1.471 eV, in epitaxial layers as well as in single crystals. In some samples, the 1.471-eV band overlaps with the broad defect band, centered at 1.450 eV. This band was first observed in epitaxial CdTe layers grown by molecular beam epitaxy (MBE). Several mechanisms have been proposed as the origin of this band: (a) bound exciton radiative mechanism; (b) recombination of bound excitons to extended states; and (c) donor–acceptor pair (DAP) transitions, for which the acceptor level is an A-center of the type V 2− Cd–Cl Te. More recently, this luminescent band has been identified as the Y luminescence band arising from excitons bound to dislocations, specifically Te(g)-type glide dislocations. In this work, we have analyzed CSVT–CdTe polycrystalline films, focusing our attention in the evolution of the defect band, by using selective pair luminescence (SPL). Our results show that the defect band consists of independent structures, one of which peaks at 1.471 eV. We carried out the study of this band as a function of both intensity of beam excitation and temperature. The change of the PL intensity as well as the change of the band maximum as a function of temperature allow us to establish that the 1.471-eV luminescent band is actually the so-called Y band observed in epitaxial layer as well as in single crystals.