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Study of the Defect Levels and Interface Properties of CdTe and CdS Polycrystalline Thin Films

Published online by Cambridge University Press:  25 February 2011

F. Abou-Elfotouh ,
S. Ashour ,
S. A. Alkuhaimi ,
J. Zhang ,
D. J. Dunlavy  and
L. L. Kazmerski
F. Abou-Elfotouh
Affiliation:
National Renewable Energy Laboratory, Golden, CO 80401
S. Ashour
Affiliation:
National Renewable Energy Laboratory, Golden, CO 80401
S. A. Alkuhaimi
Affiliation:
National Renewable Energy Laboratory, Golden, CO 80401
J. Zhang
Affiliation:
National Renewable Energy Laboratory, Golden, CO 80401
D. J. Dunlavy
Affiliation:
National Renewable Energy Laboratory, Golden, CO 80401
L. L. Kazmerski
Affiliation:
National Renewable Energy Laboratory, Golden, CO 80401
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Abstract

The properties (electrical and structural) and the defect levels dominating cadmium telluride (CdTe) films prepared by radio frequency (rf) planar magnetron sputtering, and electrochemical deposition have been determined and compared. The properties of the deposited CdTe film and the behavior of its interface with cadmium sulfide (CdS) depend strongly on the method of depositing the CdTe film, and on postdeposition heat treatments. These treatments determine various parameters crucial to the device performance, including the type and concentration of the dominant defects, interface states, and deep trap levels. Photoluminescence (PL) emission from p-type CdTe polycrystalline thin films and single crystals is reported at low temperatures (9–50 K) as well as at room temperature. The room temperature PL peak at 1.58 eV due to band-to-band recombination was observed for the first time in polycrystalline thin films. The peak location of the exciton emission is indicative of the structure perfection of the film, which is also related to the deviation from stoichiometry. The as-grown polycrystalline films are composed of a close-packed array of preferentially oriented (the [100], [110], and [111] axes aligned perpendicular to the substrate) single-crystal grains of a size in the range of 0.25–2.0 μm for the electrochemically deposited films (E-film) and 0.3–4.0 μm for rf sputtered material (rf-film). The resistivity of the heat treated E-film was substantially lower than that of the rf-film (ρ = 1.0–5.0 and 300–500 Ωcm). The performance of the CdS/(E-CdTe) devices is limited by deep levels, while the performance of die rf-CdTe device is affected by a high density of interface states.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 238: Symposium Cb – Structure and Properties of Interfaces in Materials , 1991 , 335
Copyright
Copyright © Materials Research Society 1992

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