Growth kinetics and surface properties of single-crystalline aluminum-doped zinc oxide nanowires on silicon substrates

Abstract

We present here the results from a systematic investigation on the growth kinetics and surface properties of Al-doped ZnO (AZO) nanowires synthesized on (001)Si substrates under different hydrothermal conditions. The as-synthesized vertical AZO nanowires exhibited a hydrophilic characteristic and their crystal structures were determined to be perfectly single crystalline with the axis of the wire parallel to the [0001] direction. TEM and EDS results revealed that the as-synthesized AZO nanowires have tapered tips, and the Al-doped concentration in the AZO nanowires was about 1.6at%. After a series of SEM examinations, the average length of AZO nanowires synthesized at each temperature studied was found to follow a linear relationship with the reaction time, indicating that the hydrothermal growth of AZO nanowires was a reaction-controlled process. The activation energy for linear growth of AZO nanowires on Si substrate, as obtained from an Arrhenius plot, was found to be about 46kJ/mol. From UV–vis spectroscopic measurements, it was found that the Si substrate coated with vertically-aligned AZO nanowire arrays exhibited remarkably reduced reflectance (10–12%) over a wide range of visible wavelengths (400–800nm) and angles of light incidence (8–60°). The good broadband and omnidirectional antireflection characteristics can be attributed to the light trapping effect and the graded refractive index resulting from the tapered AZO nanowire structures.