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Superficies y vacío
Print version ISSN 1665-3521
Superf. vacío vol.18 n.3 Ciudad de México Sep. 2005
Articles
Semiconductor thin films grown by RF-co-sputtering of CdTe and Al targets
* Physics Department, Centro de Investigación y de Estudios Avanzados del IPN, Apartado Postal 14-740, 07000 Mexico, D. F., México.
** CICATA-IPN, Altamira, Km 14.5 Carretera Tampico puerto-Altamira, 89600 Altamira, Tamaulipas, México.
*** Centro de Investigación y de Estudios Avanzados del IPN-Unidad Queretaro Libramiento Norponiente N° 2000, Frac. Real de Juriquilla. 76230 Querétaro, Qro., México.
CdTe is a direct bandgap semiconductor with important applications in radiation detection and photovoltaic devices. However, as any material, it has some limitations. For instance, in the photovoltaic heterostructure CdTe/CdS, among the limiting factors we may mention the difference between the cubic and the hexagonal crystallographic structures of each one of the heterostructure components and the difficulty to obtain p-type CdTe. Some of the limitations found in these systems could be surmounted by producing new materials based on CdTe. In this work we report results on the synthesis and characterization of thin films of the material Cd1-xAlxTe. This alloy is proposed based on the existence of the compounds Al2Te3 and CdAl2Te4. The semiconductors Al2Te3 and CdAl2Te4 are part of the family of vacancy ordered semiconductors formed by elements of columns II, III and VI and can be described with the general chemical formulas: AIIBIII 2CVI 4 for ternary compounds and BIII 2CVI 3for binary compounds. We have produced thin films of Cd1-x AlxTe by RF co-sputtering employing CdTe and Al targets under an Ar atmosphere. Al content was controlled by the RF power applied to the Al magnetron. The samples presented hexagonal structure as was determined by x ray diffraction. An increase in the bandgap depending on the Al content was found and values up to 1.64 eV for 3% of Al content were obtained by photoreflectance spectroscopy. The direct bandgap property is established beyond any doubt by the presence of a clear photoreflectance signal. Ellipsometry measurements show changes in CdTe-like critical points energies as result of aluminum incorporation. Electrical characterization results showed that samples present the typical characteristics of semiconductor behavior.
Keywords: Semiconductor alloys; Ordered defect semiconductors; Optical characterization
Acknowledgements
We thank the technical support of Marcela Guerrero, Ana Soto, Alejandra Garcia-Sotelo and Rogelio Fregoso. This work was partially supported by CONACyT-Mexico.
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Received: August 01, 2005; Accepted: August 29, 2005
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