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Subwavelength inhomogeneities in Cu(In,Ga)Se 2 thin films revealed by near‐field scanning optical microscopy
Author(s) -
Gütay Levent,
Pomraenke Robert,
Lienau Christoph,
Bauer Gottfried Heinrich
Publication year - 2009
Publication title -
physica status solidi (a)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.532
H-Index - 104
eISSN - 1862-6319
pISSN - 1862-6300
DOI - 10.1002/pssa.200881195
Subject(s) - full width at half maximum , photoluminescence , optics , materials science , near field scanning optical microscope , optical microscope , resolution (logic) , thin film , analytical chemistry (journal) , scanning electron microscope , physics , chemistry , nanotechnology , chromatography , artificial intelligence , computer science
We have analyzed Cu(InGa)Se 2 thin films, fabricated by standard deposition technique for solar cells, by near‐field scanning optical microscopy (NSOM) which allows for simultaneous detection of photoluminescence (PL) and AFM‐like topography. In comparison with our former confocal microscopy studies this approach yields a lateral optical resolution of ≈200 nm which is substantially below the diffraction limit. The sample is investigated by a fiber probe which guides the laser excitation to the sample surface and collects the PL signal. The recorded scans show significant lateral variations of the PL yield on length scales of 0.2–1.5 μm. By applying Planck's generalized law we extract lateral variations of the splitting of quasi‐Fermi levels Δ( E Fn – E Fp ) and optical threshold energies Δ E op,th (band gap) in the absorber. We find substantial lateral variations of these properties with Δ FWHM ( E Fn – E Fp ) ≈ 17 meV (FWHM: full width half maximum), Δ FWHM ( E op,th ) ≈ 18 meV and Δ FWHM (thickness) ≈ 220 nm. While no significant correlation between local surface topography and PL yield or Δ( E Fn – E Fp ) is observed, we find a clear anticorrelation between the optical threshold energies and the recorded height signal. Our results extend previous studies of inhomogeneity effects on solar cell absorbers towards the 100 nm regime. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)