Naslov
Compensation of donors by fast diffusors in II-VI compounds

Autori
Desnica, Uroš ; Desnica-Franković, Ida Dunja ; Magerle, Robert ; Burchard, Angela ; Deicher, Manfred

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Abstracts Book of the ICDS19 / Davies, Gordon ; Nazare, M.H., eds. - Aveiro : University of Aveiro, 1997, 14-14

Skup
ICDS19

Mjesto i datum
Aveiro, Portugal, 21.07.1997. - 25.07.1997

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
fast diffusors; Cu; II-VI; compensation

Sažetak
Fast diffusors (Cu, Ag, Au, Li...) are important impurities in semiconductors. Penetrat-ing easily, they dramatically influence electrical, optical and photoelectronic properties. In II-VI compounds they commonly compensate donor dopants in a way not fully understood. Here we present a model which explains electrical compensation of CdS by Cu: The diffusion of Cu donors into CdS provokes simultaneous creation of cadmium vacancies, VCd, which are double acceptors. Cu compensates CdS crystal indirectly, by bringing into the crystal new VCd, that pair with existing group-III donors causing their electrical compensation. Theo-retical arguments for the model are based on high bond ionicity (69%) in CdS and are analo-gous to those in truly ionic (89-96%) I-VII compounds, where the presence of II-row-atoms produces spontaneously equal number of compensating cation vacancies. Our model reconciles two widely accepted but apparently contradictory assumptions: one, that Cu in CdS is a fast diffusor which moves as an interstitial, and hence is a donor, and the other, that Cu compen-sates donors in CdS and hence effectively acts as an acceptor. To check the model experimentally, CdS samples were prepared by pre-doping pure CdS with 111In via implantation. The immediate surrounding of 111In atoms is determined by Perturbed Angular Correlation (PAC) spectroscopy. Samples were engineered by appropriate annealing to contain both, isolated In atoms in substitutional Cd lattice site, InCd+ , that are donors, and In atoms forming pairs with cadmium vacancy, VCd, at next-neighbor position, (InCd+-VCd2-)- , that are acceptors. Then Cu was evaporated on the surface of CdS. Following Cu evaporation no new, Cu related, PAC frequency was obtained, the only change being gradual increase of the (InCd+-VCd2-) component with simultaneous decrease of InCd+ component. After one week at room temperature the fraction of In atoms forming (InCd+-VCd2-)- pairs reached 100%, and the PAC signal of isolated InCd+ atoms disappeared totally. In the light of the presented model previously reported results on electrical compensa-tion of Cu doped CdS and results obtained with a number of other experimental techniques1 should be re-interpreted: Donors are compensated by cadmium vacancies which are spontane-ously created due to the presence of Cu, and trapped by donors - they are not compensated directly by Cu acceptors. Our model is compatible with the only PAC results on fast diffusors hitherto reported in II-VI´s, where Li doping also considerably increases the concentration of (In-VCation) pairs in CdS, ZnS and ZnTe, although at higher temperatures2. Considering the similarities between Cu and other fast diffusing species like Ag, Au, Na, Li... and relatively high ionicity of most II-VI compounds(49-90%), it seems plausible that the same mechanism of indirect compensation caused by diffusion-induced cation vacancies, can explain compensation effects observed for other fast diffusors in CdS and in many other II-VI compounds as well. 1T. Yamagami et al., Jpn. J. Appl. Phys. 33, 3234 (1994), J.L. Sullivan, IEEE SU-32, 71 (1985), Phys. Rev. B, 184 (1969), B. Lepley at al. J. Phys D, 12, 1917 (1979), and a number of other Cu:CdS papers. 2H. Wolf at al., Proc. 18-ICDS, Mat. Sci. Forum 196-201 (Trans. Tech Publ. 1995) p. 321

Izvorni jezik
Engleski

Znanstvena područja
Fizika

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