Optical and Related Properties of Some Synthetic Low-Dimensional Semiconductors Based on Inorganic Units

Synthetic Metals 103 (1999) 2689

Optical and Related Properties of Some Synthetic Low-Dimensional Semiconductors Based on Inorganic Units G.C. Papavassiliou, G.A. Mousdis,I. B. Koutselas,G. Pistoli?, M. G. Kanatzidisb,andA. Axtell limb Theor.Phys. Chem.Institute,NationalHellenicResearchFoundation,48, VassileosConstantinouAve., Athens 11635, Greece * NCSR,Demokritos,Athens 153 10,Greece b Dept. Chem.,Michigan StateUniv., Michigan48824,USA Abstract

The opticalandrelatedpropertiesof (Me&)&@e7, KzCd& andsimilarlow-dimensional semiconductors showexcitor& quantum confimement effects.

Keywords:UV- visible absorption,photoluminescence, photoconductivity,semiconducting films. During the last few years, a large number of lowdimensional(LD) semiconductingsystems,i.e., quantumwells (2D), quantumwires (1D) and quantumdots (OD) have been preparedand studied(for a review see[ 11). In this paper the room temperatureoptical absorption(OA), photoluminescence (PL), photoconductivity(PC) and resonanceRamanexcitation (RRE) spectraof (Mefl)zSn$Se7 121,KzCd& [3] and similar semiconductors [2-4] basedon inorganicunitsare described. Crystalsof (Me&QSn$e7 consistof S&e7 units with a 2D (antidot-like) structure. Fig. 1 showsthe OA and PL spectraof (Me&)zSn$e7 thin depositson quartz plates. The spectra exhibit strongexcitonic bands,which are blue-shiftedand more pronouncedthan thoseof the bulk (3D) materialSnSe2[5].

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Fig.2. OA(ab), PC (c,d) and RRE(e,f) spectra of K&d& (a,c,e) and CdS(b,d,f) thin deposits (a,b) and/orsinglecrystals(c,d,e,f); vertical barsindicatethe PL peakpositionsof thin depositsor singlecrystals.

Wavelength(nm)

Fig. 1. OA (a) andPL(b) spectraof (Me&)&Se7 Crystalsof K2Cd& consistof Cd& units with a quasi-2D structure. Fig.2 showsthe PA, PL, PC and RRE (:lLO-m&e) spectraof KzCd& andthoseof bulk CdS(3D),for comparison. One can seethat the excitonic peaksin the spectraof K&d& occur at shorterwavelengths(higher frequencies)than thoseof the bulk material(CdS). The spectraof KzCdsS.4 are similarto thoseobtainedfrom CdS-particles(OD-systems) of diameterca 10nm [6]. Similar results are obtained for other LD systemswith inorganic units, e.g,, (Me&)4Ge&o (OD), Na&&o (OD), IPbGeSI (ID). In all casesthe spectralpeaks, related to the excitons,aremorepronouncedandshiftedto higherfrequencies

than those of the corresponding3D materials (:quantum confinement effects) asin the casesof artificial systemsbased on conventionalsemiconductors (seefor example[I]). References

[l] G.C. Papavassihou, Progr. Sol. StateChem.,25 (1997) 125. [2] H. Ahari et al, J. Phys.Chem.,102(1998)2356. [3]E.A.AxtellIUetal,Chem. Eur.J.,2(1996) 656. [4] G. C. Papavassiliou et al, Adv. Mat.Opt.Electr. (1998). [5]Y. Bertrandet al, J. Phys.C: SoLStatePhys., 12(1979)2907. [6] G. C. Papavassiliou,J. Sol. StateChem.,40 (1981)330.

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