Self-assembled Ge islands and nanocrystals by RF magnetron sputtering and rapid thermal processing: The role of annealing temperature

Abstract

Germanium (Ge) nanostructures were fabricated through the rapid thermal processing of radio frequency sputtered Ge on silicon (Si). The substrates were unheated during the growth, resulting in a post-growth Ge deposited layer that was 250nm thick with a surface that had no evidence of nanostructure formation. The samples subsequently underwent rapid annealing from 400°C to 800°C for 15s. Dramatic nanostructuring was observed at the surface following annealing above 600°C. Scanning electron microscopy showed that as annealing temperatures increased, the Ge layer evolved into circular islands. The sizes of the Ge islands increased and the islands became more uniform and dense at 700°C. Viable Ge nanocrystals were obtained at 600°C and 700°C given the increased annealing temperatures that improved crystallinity. The calculated Raman line shape based on the phonon confinement model agreed well with the experimental spectrum which constituted crystalline Ge nanostructures with an estimated size of 2.65–3.5nm. In addition, no Ge–Si intermixing was observed at the interface. High resolution X-ray diffraction revealed the tetragonal Ge phases and the samples were of polycrystalline structures. The annealing temperature also enhanced photo currents of the fabricated metal semiconductor metal photodetector. These results suggest that 700°C for 15s is an optimum annealing temperature for the production of viable crystalline Ge nanostructures.