Journal
MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING
Volume 37, Issue -, Pages 37-45Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.mssp.2015.01.002
Keywords
Graded CIGS layer; Na doping; TMPCD; Minority lifetime
Categories
Funding
- CONACyT
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In the present work we have studied the effect of Na on the properties of graded Cu (In1-xGax)Se-2 (CIGS) layer. Graded CIGS structures were prepared by chemical spray pyrolysis at a substrate temperature of 350 degrees C on soda lime glass. Sodium chloride is used as a dopant along with metal (Cu/In/Ga) chlorides and n, n-dimethyl selenourea precursors. The addition of Na exhibited better crystallinity with chalcopyrite phase and an improvement in preferential orientation along the (112) plane. Energy dispersive analysis of X-rays (line/point mapping) revealed a graded nature of the film and percentage incorporation of Na (0.86 at%). Raman studies showed that the film without sodium doping consists of mixed phase of chalcopyrite and CuAu ordering. Influence of sodium showed a remarkable decrease in electrical resistivity (0.49-0.087 Omega cm) as well as an increase in carrier concentration (3.0 x 10(18)-2.5 x 10(18) cm(-3)) compared to the undoped films. As carrier concentration increased after sodium doping, the band gap shifted from 1.32 eV to 1.20 eV. Activation energies for un-doped and Na doped films from modified Arrhenius plot were calculated to be 0.49 eV and 0.20 eV, respectively. Extremely short carrier lifetimes in the CIGS thin films were measured by a novel, nondestructive, noncontact method (transmission modulated photoconductive decay). Minority carrier lifetimes of graded CIGS layers without and with external Na doping are found to be 3.0 and 5.6 ns, respectively. (C) 2015 Published by Elsevier Ltd.
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