Fig. 5: Composition-dependent CuInSe2 surface reactivity against KCN at room temperature.
From: Chemical instability at chalcogenide surfaces impacts chalcopyrite devices well beyond the surface
a SEM top views of Cu-poor CIS (CIS-P, top row) and Cu-rich CIS (CIS-R, bottom row) films unetched (KCN-U) and after KCN weak (KCN-W) and bold (KCN-B) etchings. The white squares are magnifications of selected areas to reveal the presence of Cu2Se particles in PU and RW and their absence in RB. b Box plot of Cu/In and (Cu+In)/Se atomic concentration ratios acquired by EDS at 7 kV (top) and 20 kV (bottom) acceleration voltages, entailing beam-film interactions as shown by the corresponding CASINO73 depth simulations. The dashed lines correspond to the ratios expected from pure stoichiometric CuInSe2 (grey) and Cu2Se (cyan). It is noteworthy that the Cu/In ratio of CIS-R exceeds 1 even at 20 kV, because the sample was intentionally grown under very high Cu flux, whereas the initial Cu/In ratio of standard Cu-rich films never exceed 1.3. c Cu and Se SIMS depth profiles of CIS-P (red), CIS-S (black) and CIS-R (blue) films subject to KCN-W (light shades) and KCN-B (dark shades). Cu and Se appear to be leached mostly out of CIS-R, whereas CIS-S shows the least compositional deviation. The Se profiles of CIS-P and CIS-S are virtually unaffected by KCN etching. d, e Schematic representations of point defect-driven selective leaching by KCN.
