Enhanced optical absorption and photoresponse of glancing angle deposited CIGS nanorods

Abstract

Nanostructured materials have become an attractive alternative to their thin film and bulk counterparts in photovoltaic and photoconductivity research. This is mainly attributed to their superior optical and electrical properties. Light trapping in vertically aligned nanostructures results in high optical absorption and provides lower dark current and enhanced carrier lifetime by utilizing an anode and cathode via a metal capping process that isolates each nanorod. The combination of these two features can potentially lead to the development of high efficiency nanostructured devices including solar cells, photodiodes, and photodetectors. Results from optical absorption and responsivity properties of nanorod arrays of CuInGaSe2 (CIGS), a p-type semiconductor with a wide band gap ranging from 1.0 eV to 1.7 eV, are compared to their thin film counterpart. Utilizing an RF sputtering system, glancing angle deposition (GLAD) technique was used to grow CIGS nanorods while conventional films were fabricated by normal incidence deposition. Scanning electron microscopy (SEM) images indicated a successful growth of CIGS nanorods. Optical reflection was found to be strongly altered by the presence of the nanorod structures through spectroscopic reflectometry and photoresponse was greatly enhanced with an enhancement factor of 7X in fabricated devices.