Sputter Deposition of CuInSe 2 and CuGaSe 2 from Composite Targets on (100) Si
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1210-Q03-25
Sputter Deposition of CuInSe2 and CuGaSe2 from Composite Targets on (100) Si. Okechukwu N. Akpa1, Shaik Shoieb2, Trenton R. Thompson2, Tamara F. Isaacs-Smith3, Philip Anderson4, Supapan. Seraphin4, and Kalyan K. Das2. 1
Tuskegee Center for Advanced Materials, Tuskegee University, Tuskegee AL 36088, U.S.A.
2
Department of Electrical Engineering, Tuskegee University, Tuskegee AL 36088, U.S.A.
3
Space Research Institute, Auburn University, Auburn AL 36830, U.S.A.
4
Department of Material Science and Engineering University of Arizona, Tucson AZ 85721,
U.S.A.
ABSTRACT Thin films of CuInSe2 (CIS) and CuGaSe2 (CGS) were deposited on (100) Si substrates by RF magnetron sputtering using stoichiometric targets, at various substrate temperatures. Prior to film deposition, the Si substrates were cleaned using the RCA cleaning procedure and treated in a buffered oxide etch (BOE) solution. Deposited films were characterized using Rutherford backscattering spectroscopy (RBS), transmission electron microscopy (TEM) of cross-sectional samples and Hall measurements. Rutherford backscattering analysis indicated that the CIS films had a composition of Cu0.8In1.1Se1.9, whereas CGS films were Cu-poor and Ga-rich with a composition of Cu0.3Ga1.5Se1.5. Clean Cu-chalcopyrite/Si interfaces were obtained using BOE treated Si substrates. Transmission electron micrographs of cross-sectional samples indicated a polycrystalline film structure and that the native oxide on the Si substrate was eliminated. Energy dispersive X-ray spectroscopy (EDS) conducted in the TEM showed that contamination levels in the films were low. The Hall-mobility experiments performed the CIS film indicated that the material was of p-type conductivity with a carrier concentration of 9.6 x 1020/cm3 and a Hall mobility of 390 cm2V-1s-1. INTRODUCTION Chalcopyrite material systems have been extensively studied for the fabrication of thin film solar cells. In particular, quaternary CIGS, with 20/80 In/Ga, as an absorber film in a heterojunction structure have yielded high conversion efficiencies close to 20% [1]. However, it has been predicted theoretically that CGS films will have even higher conversion efficiencies, although not realized so far [2]. Therefore, in the present study we consider the growth and characterization of CIS and CGS films individually in order to develop an understanding of the behavior of chalcopyrite material systems as absorber films in thin film solar cells. EXPERIMENT Silicon wafers with a (100) orientation, and a diameter 75 and 100 mm were used as substrates for the deposition of CIS and CGS films. The wafers were cleaned using the standard RCA cleaning procedure and buffered oxide etch (BOE) treated prior to loading the sputtering chamber. Film growth was achieved using an AJA International Orion-5 RF magnetron
sputtering system at a power of 65 W. A substrate temperature ranging from 300o C to 530o C was maintained during film growth. Following film deposition the wafers were diced into 1 cm x 1 cm samples for characte
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