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DTSTAMP:20260416T081608
DTSTART:20130828T110000
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URL:https://murmitoyen.com/events/vanille/udem/detail/274328
LOCATION:Université de Montréal - Pavillon Roger-Gaudry\, 2900\, chemin d
 e la Tour\, Montréal\, QC\, Canada\, H3T 1J6
SUMMARY:Evidence of two-step processes in the structural relaxation of amor
 phous silicon
DESCRIPTION:Leonardus B. Bayu Aji\, Department of Electronic Materials Eng
 ineering\, Research School of Physics and Engineering\, Australian Nationa
 l University\, Canberra\, 0200\, Australia. Studies of (pure) ion-implant
 ed amorphous silicon (a-Si) show that\, during thermal annealing\, the Si-
 Si network undergoes extensive restructuring toward a state of lowest free
  energy\, a process called structural relaxation. However\, despite this b
 eing the focus of much research\, the mechanism(s) that govern the kinetic
 s of the structural relaxation still remain unclear. The work presented he
 re addresses this issue.Annealing of a-Si leads to a change in its mechani
 cal\, vibrational\, and electrical properties\, whereby these properties a
 re sensitive to the degree of relaxation. The effect of annealing temperat
 ures up to 550ºC on the mechanical behavior of a-Si was studied using nan
 oindentation by measuring the probability of a pressure-induced phase tran
 sition. The changes in the covalent Si-Si network were further tracked usi
 ng Raman microspectroscopy and electrical measurements. The mechanical be
 havior of a-Si is very sensitive to the ‘state’ (relaxed or unrelaxed)
  of the amorphous network\, whereby unrelaxed (as-implanted) a-Si deforms 
 plastically via flow and relaxed (thermally annealed) a-Si via a pressure-
 induced phase transformation. The probability of phase transformations is 
 found to change significantly in a very narrow temperature range from 300
 ºC to 350ºC during thermal annealing. In contrast\, the reduction in the
  average tetrahedral bond-angle distortion (Δθb) from 10.8º to 9.4º as
  observed by Raman microspectroscopy occurs at slightly higher temperature
 s\, namely over a temperature range centered at 370ºC. Previous experime
 nts have shown that the electrical conduction in amorphous semiconductors 
 occurs via variable-range hopping of the charge carriers in localized stat
 es\, e.g. dangling bonds\, near the Fermi level. This is characterized by 
 Mott's variable-range hopping relation. Thus\, conductivity measurements i
 n a-Si as a function of annealing temperature provide additional informati
 on on the evolution of the density of the dangling bonds and the role of d
 efect annihilation during structural relaxation. The conductivity\, and he
 nce the density of dangling bonds\, is found to progressively decrease fro
 m 1021 eV-1 cm-3 to 1019 eV-1 cm-3 with annealing temperature. A major dec
 rease in the density of the dangling bonds was observed around an annealin
 g temperature of 250ºC\, significantly lower than the temperatures where 
 a reduction in Δθb or the probability for phase transformations occurs.
  This strongly suggests that structural relaxation is at least a two-step
  process involving first a reduction in defects and dangling bond density 
 followed by a reduction in the average tetrahedral bond-angle distortion a
 s second step. Site web du groupe de  Dr. Bimo Bayu AjiCette conférence 
 est présentée par le RQMP Versant Nord du Département de physique de l
 'Université de Montréal et le Département de génie physique de Polytec
 hnique Montréal.
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