Electron Spin Resonance and Ultra Violet (UV) Photoluminescence of Ge Implanted CuGaSe 2 Thin Films Prepared by the CCSV
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1012-Y12-19
Electron Spin Resonance and Ultra Violet (UV) Photoluminescence of Ge Implanted CuGaSe2 Thin Films Prepared by the CCSVT (Chemical Close-Spaced Vapor Transport) Technique Serge Doka1, Jasmin Hofstetter1, Marin Rusu1, Ernest Arushanov2, Lips Klaus3 , Thomas Schedel-Niedrig1, and Martha Ch. Lux- Steiner1 1 Hahn- Meitner Institut GmbH Berlin, Glienicker Strasse 100, Berlin, D-14109, Germany 2 Institute of Applied Physics, Academy of Sciences,Academiei 5, Chisinau, 277028, Moldova 3 Hahn- Meitner Institut GmbH Berlin, Kekulestrasse 5, Berlin, D-12489, Germany ABSTRACT Non-equilibrium ion implantation of Ge in p-type polycrystalline thin film CuGaSe2 (CGSe) prepared by Chemical Close-spaced Vapor Transport (CCSVT) has been performed with the goal to achieve n-type doping of this chalcopyrite semiconductor. Using Electron Spin Resonance (ESR) it is shown that Ge implantation induces a paramagnetic species at g = 2.003. A model is proposed that assigns the ESR signal to electrons trapped by donor states that are electrically inactive. Moreover, UV photoluminescence of Ge implanted films has evidenced a new peak emission at 1.47 eV, which is resolved as a radiative recombination of a hole bound to the native copper vacancy and an electron bound to a new deep donor with an ionization energy of E D =360±10 meV.
INTRODUCTION The Cu- chalcopyrite semiconductors have been successfully employed for the preparation of high efficiency thin films solar cells. While CuInSe2 can be grown both p and n- type, CuGaSe2 (CGSe) is always obtained p-type [1]. The preparation of n-type CGSe material requires shifting the Fermi level close to the conduction band gap under nonequilibrium conditions where the formation of Cu vacancies may be kinetically avoided [2]. Hence, obtaining n-type conduction in the larger gap CGSe is a crucial step towards designing future cells with CGSe as absorber material. With the aim to achieve it, Ge ions were implanted into CGSe thin films in this work. In this contribution, the understanding of the main effects of Ge implantation on CCSVT-grown CGSe thin films obtained by electron spin resonance (ESR) and Ultra- violet photoluminescence (UV- PL) are reviewed.
EXPERIMENTAL DETAILS The Ge atomic concentration of both annealed and as-implanted polycrystalline CGSe samples were determined by Secondary Neutral Mass Spectroscopy (SNMS). The UV photoluminescence (λexc = 351.1 nm) with a penetration depth which matches well the Ge depth profile into the implanted and annealed CGSe films was used for defects characterization. ESR spectra were recorded in a continuous-wave (cw) ESR spectrometer operating at X-band microwave frequencies (9.5 GHz). For magnetic resonance measurements, Ge implanted and annealed CGSe thin films deposited on Mo coated Soda Lime Glass substrate were peeled off from the substrate by ESR silent adhesive Tesa-tape and then rolled up and place in a evacuated, filled and sealed ESR quartz tube. Details on samples handling for ESR are presented elsewhere [3] and all the Ge implanted s
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