Comments on the Behaviour of the Absorption Edge of Cd_1−xMn_xTe for x > 0.4

Abstract

A pinning of the absorption edge of Cdl-,Mn,Te occurs for x > 0.4. Some authors have attributed this behaviour to a transition within the 3d5 localized levels of the Mn2+ ions. The possibility is analysed to observe such a transition in CdMnTe. A comparison with observations on spectra of various substitutional impurities of the 3d series on 11-VI crystals leads to the determination of an upper limit for the crystal field parameter Dq of the Mn atom in CdMnTe crystals and consequently to a lower limit for the energy difference between the ground and the first excited states in the d-shell of Mn. From a temperature and composition dependence recall of absorption and luminescence measurements previously performed, it is deduced that transitions between 3d5 levels of Mn2+ do not explain the anomalous behaviour of the absorption edge of CdMnTe for x > 0.4 and an alternative possible explanation is given.Ein Festsetzen der Absorptionskante von Cdl-,IvIn,Te tritt fur x > 0,4 auf. Einige Autoren ordnen dieses Verhalten einem Ubergang innerhalb der lokalisierten 3d5-Niveaus der Mn2+-Ionen zu. Die Moglichkeit der Beobachtung eines solchen ubergangs in CdMnTe wird analysiert. Ein Vergleich mit Beobachtungen an Spektren von verschiedenen Substitutionsverunreinigungen der 3d-Serien an 11-VI-Kristallen fuhrt zur Bestimmung einer oberen Grenze fur den Kristallfeldparameter Dq des Mn-Atoms im CdMnTe-Kristall und folglich zu einer unteren Grenzs fur die Energiedifferenz zwischen dem Grundzustand und dem ersten angeregten Zustand in der d-Schale des Mn. Aus der Temperatur-und Zusammensetzungsabhangigkeit von friiheren Absorptions-und Lumineszenzmessungen wird abgeleitet, daB ubergange zwischen den 3d5-Niveaus von MnZt das anomale Verhalten der Absorptionskante des CdMnTe fur x >0,4 nicht erklaren und es wird eine mogliche alternative ErklLrung vorgeschlagen.

Pressure dependence of the optical absorption edge in Cd1-xMnxTe

“…n=O where E"(k) is the band energy for crystals formed from the different nearest-neighbour configurations that can occur in alloys. Theoretical research [20] showed that the alloy band structure calculated according to (8) is in good agreement with experiment with regards to the valence bands and band gap bowing than that of usual treatments of alloys using the VCA and coherent potential approximation (CPA) [20]. As seen from ( 7), the n = 2 ordered structure possesses the largest probability at x = t .…”

“…The anomaly in the absorption edge occurs at large Mn-composition withx ranged between 0.5 to 0.7, the change of rlsv( pd) with composition is too small to measure [23] in comparison to that of Tl,(s). This might possibly be the reason why the absorption edge is almost concentration independent at large Mn-composition as found in [8]. However, at higher Mn-composition, the quick increase in AEPd with increasing pressure would result in a quick upward shift in rlSv( pd) as compared with that of the lower composition, and then a lower absorption edge and a larger negative pressure coefficient should be expected with increasing the composition under pressure.…”

“…Considering the fact [3] that the well-defined different nearest-neighbour Cd-Te and Mn-Te distances (a 'bimodel' distribution) exist in Cd, -,Mn,Te, the local bonding observed in Cdl -,Mn,Te [3] is similar to that found in the chalcopyrite structure. In addition, the antiferromagnetic coupling between nearest neighbours over Mn sites only can be presented apparently in our model as to simulate the properties of the suggested AF ordered phase at high x-concentration [ 11, We therefore believe that the electronic structure calculated for the probable chalcopyrite structure could reflect the main features of that of the Cdo,5Mno,5Te alloy though we did not calculate the weighted averages of the band structures with different configurations n in (8). Such a chalcopyrite analogue had also been used to assist in the modelling of the random ZB solid solution in the alloys of Ga,-,In,As [21], Al,Gal-,As and GaAs,Sbl-, [22].…”