Existence and removal of Cu ₂Se second phase in coevaporated Cu ₂ZnSnSe ₄ thin films

The composition dependence of the electrical properties of Cu ₂ZnSnSe ₄ thin films synthesized by coevaporation and the results of phase analyses are reported. We found that the hole concentration depends on the Cu/(Zn Sn) ratio and is on the order of 10 ¹⁷ cm ^-3 for the ratio of 0.7 and increases to over 10 ²⁰ cm ^-3 when the ratio exceeds 0.9. Raman spectra indicate the coexistence of semimetallic Cu ₂Se second phase in the thin films with Cu/(Zn Sn) ratio above 0.9. In order to remove the Cu ₂Se phase selectively, we attempted a KCN etching. After the KCN etching for 30 min, the Raman peak attributed to the Cu ₂Se phase disappeared, and the hole concentration decreased to about 10 ¹⁸ cm ^-3. © 2012 American Institute of Physics.