Annealing temperature effect on structure and electrical properties of films formed of Ge nanoparticles in SiO₂

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• 作者：Ionel Stavarache ; Ana-Maria Lepadatu ; Toma Stoica ; Magdalena Lidia Ciurea
• 关键词：Ge&ndash ; SiO2 films ; Ge nanocrystals ; Raman spectroscopy ; Electrical behaviour ; AFM
• 刊名：Applied Surface Science
• 出版年：15 November, 2013
• 年：2013
• 卷：285
• 期：part_PB
• 页码：175-179
• 全文大小：1682 K

文摘

Ge-SiO₂ films with high Ge/Si atomic ratio of about 1.86 were obtained by co-sputtering of Ge and SiO₂ targets and subsequently annealed at different temperatures between 600 and 1000 掳C in a conventional furnace in order to show how the annealing process influences the film morphology concerning the Ge nanocrystal and/or amorphous nanoparticle formation and to study their electrical behaviour. Atomic force microscopy (AFM) imaging, Raman spectroscopy and electrical conductance measurements were performed in order to find out the annealing effect on the film surface morphology, as well as the Ge nanoparticle formation in correlation with the hopping conductivity of the films. AFM images show that the films annealed at 600 and 700 掳C present a granular surface with particle height of about 15 nm, while those annealed at higher temperatures have smoother surface. The Raman investigations evidence Ge nanocrystals (including small ones) coexisting with amorphous Ge in the films annealed at 600 掳C and show that almost all Ge is crystallized in the films annealed at 700 掳C. The annealing at 800 掳C disadvantages the Ge nanocrystal formation due to the strong Ge diffusion. This transition in Ge nanocrystals formation process by annealing temperature increase from 700 to 800 掳C revealed by AFM and Raman spectroscopy measurements corresponds to a change in the electrical transport mechanism. Thus, in the 700 掳C annealed films, the current depends on temperature according to a T^鈭?/2 law which is typical for a tunnelling mechanism between neighbour Ge nanocrystals. In the 800 掳C annealed films, the current-temperature characteristic has a T^鈭?/4 dependence showing a hopping mechanism within an electronic band of localized states related to diffused Ge in SiO₂.