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

Transmission electron microscopy (TEM) has been used to investigate thedamage 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 buriedamorphous layer; and the defect structures produced following thermal annealsof 400°C, 600°C or 800°C for 30 minutes. Analysis of these samples yieldedresults which suggested that the Xe gas contained within the amorphous layerswas swept by the amorphous/crystalline interfaces during solid phase epitaxialre-crystallisation (SPEG) into large bubbles elongated along a directionperpendicular to the interfaces. In order to further investigate this sweepingeffect, buried amorphous layers were produced in Si by implanting Li at liquidnitrogen temperature and post implanting the layers with IxlO 16 He ions/cm 2 .Contrary to the spherical bubbles produced under similar conditions incrystalline Si, irregular shaped bubbles were formed in the amorphous layer.Results from in-situ TEM studies showed that these bubbles are mobile attemperatures lower than expected in crystalline Si. Thus, upon reaching themoving interfaces between amorphous and crystalline Si, the bubbles are forcedback into the amorphous material which ultimately results in coalescence of thegas into larger bubbles once the two interfaces combine. In addition, microtwinshave been shown to form in regions of the re-crystallising layer where thereexists an excess of interstitial-type defects. This is contrary to previous microtwinnucleation models which suggested that microtwins are either formed on [111]planes or on bubbles.

Level dc:type.qualificationlevel

Doctoral (Level 8)

Year dc:date.issued

2008

Author dc:creator

• Gandy, AS

Language dc:language

en

Identifier

oai:salford-repository.worktribe.com:1337175

OAI identifier oai:identifier

oai:salford-repository.worktribe.com:1337175