A transmission electron microscopy study of the interaction between defects in amorphous silicon and a moving crystalline/amorphous interface

Gandy, AS

Abstract

Transmission electron microscopy (TEM) has been used to investigate the
damage produced following high temperature (350°C) Xe implantation into (100)
Si at fluence (>lx!0 16 Xe ions/cm 2 ) and energy (250keV) which produce a buried
amorphous layer; and the defect structures produced following thermal anneals
of 400°C, 600°C or 800°C for 30 minutes. Analysis of these samples yielded
results which suggested that the Xe gas contained within the amorphous layers
was swept by the amorphous/crystalline interfaces during solid phase epitaxial
re-crystallisation (SPEG) into large bubbles elongated along a direction
perpendicular to the interfaces. In order to further investigate this sweeping
effect, buried amorphous layers were produced in Si by implanting Li at liquid
nitrogen temperature and post implanting the layers with IxlO 16 He ions/cm 2 .
Contrary to the spherical bubbles produced under similar conditions in
crystalline Si, irregular shaped bubbles were formed in the amorphous layer.
Results from in-situ TEM studies showed that these bubbles are mobile at
temperatures lower than expected in crystalline Si. Thus, upon reaching the
moving interfaces between amorphous and crystalline Si, the bubbles are forced
back into the amorphous material which ultimately results in coalescence of the
gas into larger bubbles once the two interfaces combine. In addition, microtwins
have been shown to form in regions of the re-crystallising layer where there
exists an excess of interstitial-type defects. This is contrary to previous microtwin
nucleation models which suggested that microtwins are either formed on [111]
planes or on bubbles.

• Thesis Type: Thesis
• Deposit Date: Aug 17, 2021
• Award Date: Nov 1, 2008