Synthesis of germanium nanodots on silicon using an anodic alumina membrane mask

Abstract

We explore here the use of an anodic alumina membrane as a mask for the fabrication of highly ordered nanodots. The masks were synthesized using a two-step anodization process of aluminum foils in acid solutions. Masks that contain highly ordered pores with aspect ratios of 4:1 to 1:1 were obtained by controlling the duration of the second anodization and the time to remove the buried layer. The size of the pores can be varied from 10 to 200 nm depending on the anodization acid used or the anodization voltage. Germanium (Ge) nanodots on silicon (Si) were obtained by evaporating Ge onto the Si wafer through the mask. The height of the nanodots can be controlled via the deposition rate and duration of the Ge films. The spacing between nanodots can be varied by immersing the mask in phosphoric acid to enlarge the pores. We have fabricated a metal–insulator–semiconductor memory structure with Ge nanodots embedded in silicon oxide matrix as the insulator layer. The nanodots have a diameter of 80 nm and a density of ∼10 10 cm −2. The capacitance versus voltage characteristics of these devices exhibited a charge storage capacity of 9.0×10 11 Ccm −2.