Near-IR absorption saturation and mechanism of picosecond recovery dynamics of copper selenide nanostructured via alumina

Absorption saturation at 1.064 mu m wavelength in Cu(2-x)Se material nanostructured by means of an original method-formation and hosting in an array of electrochemically grown alumina voids was investigated. Columnlike channels provide growth of copper selenide in a shape of nanowire with a fixed diameter. Experimental results obtained from measuring nanowires of various diameters (circle divide 10, 15, 20, and 70 nm) revealed that the circle divide 20 nm case is most efficient for absorption saturation, manifesting highest optical modulation depth and lowest interlevel transition rate evaluated. A model to analyze the conditions for absorption saturation and absorption recovery dynamics was developed. Depending on pump intensity the nonmonotonous increase in recovery time for the highest applied values was interpreted as filling up of states at an intermediate energy level. From modeling, important material science parameters, such as concentration of resonant and trapping/recombination states, interlevel transition rate, capture time, characteristic for copper selenide, have been evaluated and compared for different samples. Finally, the consequence of the model to a working copper selenide energy level scheme was considered. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3140612]