AVS 52nd International Symposium
    Thin Films Monday Sessions
       Session TF-MoP

Paper TF-MoP32
Growth and Properties of CdTeO@sub x@ Films by Reactive rf Magnetron Sputtering: CdTeO@sub 3@ a High-quality Transparent Material for Solar Cell Applications

Monday, October 31, 2005, 5:00 pm, Room Exhibit Hall C&D

Session: Aspects of Thin Films Poster Session
Presenter: J. Carmona-Rodríguez, Benemérita Universidad Autónoma de Puebla, Mexico
Authors: S. Jiménez-Sandoval, Centro de Investigación y de Estudios Avanzados del IPN, Mexico
J. Carmona-Rodríguez, Benemérita Universidad Autónoma de Puebla, Mexico
R. Lozada-Morales, Benemérita Universidad Autónoma de Puebla, Mexico
O. Jiménez-Sandoval, Centro de Investigación y de Estudios Avanzados del IPN, Mexico
M. Meléndez-Lira, Centro de Investigación y de Estudios Avanzados del IPN, Mexico
C.I. Zúniga-Romero, Centro de Investigación y de Estudios Avanzados del IPN, Mexico
Correspondent: Click to Email
CdS/CdTe heterostrtuctures is one of the leading solar cell technologies nowadays. One of the current approaches is the use of thin (~ 100 nm thick) CdS layers to improve cell efficiency. However, as the thickness of the CdS layer is reduced there is a greater chance for the appearance of micro junctions between the p-type CdTe layer and the transparent conducting oxide used as front contact, reducing cell efficiencies. It has been recently suggested that the use of a highly resistive buffer layer could avoid micro shunt formation. In order to gain further insight on the formation of transparent CdTe-based materials, we report on the properties of CdTeO@sub x@ films grown by reactive rf sputtering and of films annealed after deposition. The films were grown under an argon flow of 12 sccm and using oxygen flows of 0, 3, 5, 7, 8, 9, 9.5, 10, 10.5 and 11 sccm. This range of oxygen flows was equivalent to oxygen partial pressures within the chamber from 6.7 x 10@super -5@ (3 sccm) to 1.1x10@super -4@ Torr (11 sccm). The substrate temperature was maintained at 400°C for all growths with deposition times of 35 minutes at 35 W of power applied to the 99.999% pure CdTe target. The X-ray diffraction results indicate that the structure of the films was a mixture of cubic/hexagonal phases, typical of CdTe films, for films grown with oxygen flows of up to 10.5 sccm. This structure, however, is no longer sustained when the oxygen flow reaches 11 sccm. At this point, the X-ray diffraction peaks narrow because the material reaches the stoichioimetry and structure of high-quality CdTeO@sub 3@. Accordingly, the bandgap increases from 1.50 to 1.67 eV as the oxygen flow increases from 3 to 10.5 sccm, and at 11 sccm the band gap jumps to 3.73 eV, becoming a transparent, highly resistive film. Annealing the films for two hours under an inert atmosphere at 450°C does not produce significant changes in the crystalline structure, optical properties or bandgap values.