Tunable Photoconduction Sensitivity and Bandwidth for Lithographically Patterned Nanocrystalline Cadmium Selenide Nanowires

Nanodystalline cadmium selenide (nc-CdSe) nanowires were prepared using the lithographically patterned nanowire electrodeposition method. Arrays of 350 linear nc-CdSe nanowires with lateral dimensions of 60 nm (h) x 200 nm (w) were patterned at 5 mu m pitch on glass. nc-CdSe nanowires electrodeposited from aqueous solutions at 25 degrees C had a mean grain diameter, d(ave), of 5 nm. A combination of three methods was used to increase d(ave) to 10, 20, and 100 nm: (1) The deposition bath was heated to 75 degrees C, (2) nanowires were thermally annealed at 300 degrees C, and (3) nanowires were exposed to methanolic CdCl2 followed by thermal annealing at 300 degrees C. The morphology, chemical composition, grain diameter, and photoconductivity of the resulting nanowires were studied as a function of d(ave). AS d(ave) was increased from 10 to 100 nm, the photoconductivity response of the nanowires was modified in two ways: First, the measured photoconductive gain, G, was elevated from G = 0.017 (d(ave) = 5 nm) to similar to 4.9 (100 nm), a factor of 290. Second, the photocurrent rise time was increased from 8 mu s for d(ave) = 10 nm to 85 far 100 nm, corresponding to a decrease by a factor of 1 million of the photoconduction bandwidth from 44 kHz to 44 mHz.