1.4-eV photoluminescence and thermally stimulated conductivity in cadmium telluride

Abstract

Photoluminescence (PL) and thermally stimulated conductivity (TSC) data on high-resistivity, p-type CdTe single crystals are presented. The PL emission in these samples consists of two closely overlapping components peaking at approximately 1.47 and 1.49 eV. Thermal quenching of these signals reveals activation energies of ∼0.02 and ∼0.13 eV for the former component, and ∼0.11 eV for the latter. TSC signals at temperatures corresponding to those over which thermal quenching occurs are observed. The TSC peaks are due to hole release with activation energies which agree with those obtained from the thermal quenching studies. Etching of the samples removes surface damage caused by mechanical polishing. The surface damage produces nonradiative pathways by which electron-hole recombination can take place without luminescence. A model based on free-electron to trapped-hole recombination is presented to account for the data. It is shown, from numerical solutions of the rate equations describing the model, that by explicitly incorporating into the model more than one hole state at which radiative recombination can occur, shifts in the emission energy during time-resolved and intensity-dependence studies can be expected.

Heavy metal doping of CdTe crystals

“…In addition, these last peaks are practically negligible at 50 K, whereas (X) and 1.47 eV peak are still present at 70 K. This confirms our hypothesis that the 1.47 eV peak is not directly related to the 1.4 eV band. The same behavior was assigned to the specie As in nominal pure CdTe with As as impurity [28]. Usually, emissions in this region are associated with V and related species [29].Therefore, this peak may be related to the amphoter behavior of the heavy metals, involving the specie M (with M heavy metal), and probably been associated to the dopant TABLE III ACTIVATION ENERGY FOR THE DIFFERENT PEAKS OF THE PL SPECTRA FOR EVERY DOPANT TABLE IV THERMAL ENERGY COEFFICIENT FOR THE DIFFERENT DOPANTS self-compensation.…”

Does the low-temperature Arrhenius plot of the photoluminescence intensity in CdTe point towards an erroneous activation energy?

“…For a continuous band, as an order of magnitude, ⌽ D Ϸ 1 and at 10 K D Ϸ 3 ϫ 10 11 s Ϫ1 . 6 The parameter ␣ 1 is proportional to and quite high values of ␣ 1 are expected-but are not found experimentally. To overcome this problem a two-acceptorlevels model was proposed by Cotal et al in Ref.…”

“…In this model the low-temperature quenching was explained as a thermal transition of holes from one level to another. The transition between two localized levels may indeed have a very small transition probability because of a low value of the parameter ⌽ D .There were also two PL bands visible in the spectra of Cotal et al 6 thus, additionally, giving justification to the assumption of two different activation energies. It is worth noticing, however, that in the low-temperature region activation energies generally of the order of E T Ϸ 10 meV have been found in widely different materials, such as ZnSe, 7 CdS, 8 and GaP.…”

Microstructure and point defects in CdTe nanowires for photovoltaic applications

“…There is some evidence in the literature that weak phonon coupling is a signature of transitions associated with extended defects or surfaces. Emission at 1.49 eV for example, has been linked to surfaces [37,38] although not without controversy [39]. Of all the samples A-F examined, only E and F showed visible signs of degradation in the SEM, with roughening of the sidewalls being observed for most of the NWs.…”