Scanning tunneling microscopic analysis of Cu(In,Ga)Se2 epitaxial layers

Abstract

Scanning tunneling microscopy (STM) measurements have been made on single-crystal epitaxial layers of CuInSe2 grown on GaAs substrates. Results were obtained for as-grown, air-exposed, and cleaned surfaces; in situ cleaved surfaces; surfaces sputtered and annealed in the STM system; and samples prepared by a light chemical etch. Conventional constant-current topographs, current-voltage curves, and current imaging tunneling spectroscopy (CITS) scans were obtained. Topographic images show that the surfaces appear rough on the atomic scale and often exhibit regular features consistent with a previously proposed surface ad-dimer reconstruction. CITS scans show a spatially varying energy gap consistent with band-edge fluctuations on a scale of a few atomic spacings. Energy variations were observed in both band edges. Although quantitative description of the magnitude of these fluctuations is difficult, the fluctuations on the atomic scale appear much larger than observed by methods such as photoluminescence, which average over larger volumes.

Scanning tunneling spectroscopy of epitaxial silver indium diselenide

“…To illustrate the differences between AIS and CIS, we compare the present data to previously obtained STS data on CIS [29]. Fig.…”

“…Fig. 5b shows band edge fluctuation data for three sections of a line spectrum constructed from data in Mayer et al [29], denoted by circles, triangles, and squares.…”

“…Fig. 5b shows the band edge positions for the CIS surface taken from previously published work [29]. Three sections of the line were plotted, each denoted with a different shape: circle, triangle, or square.…”

Scanning tunneling microscopy as a probe of defects in CuInSe<inf>2</inf>

“…[12] The nature of the defects giving rise to the band tails is currently unknown, although one may presume that individual point defects or defect clusters have a strong effect on the results. [10] Here we present further data on the effect of point defects in CIS on local electronic structure of the material at the atomic scale.…”

“…Excellent performance has been replicated at a number of laboratories with the highest performance near 20% efficiency. [1] A wide range of studies, primarily using photoluminescence, of CuInSe 2 have shown significant band tails to occur in these materials [2][3][4][5][6][7][8][9][10][11] In one study it was concluded that the performance of solar cells may depend directly upon the band tail width. [12] The nature of the defects giving rise to the band tails is currently unknown, although one may presume that individual point defects or defect clusters have a strong effect on the results.…”