TY - JOUR
T1 - Surface morphology of amorphous germanium thin films following thermal outgassing of SiO 2 /Si substrates
AU - De Los Santos Valladares, L.
AU - Dominguez, A. Bustamante
AU - Llandro, J.
AU - Holmes, S.
AU - Quispe, O. Avalos
AU - Langford, R.
AU - Aguiar, J. Albino
AU - Barnes, C. H.W.
N1 - Funding Information:
This work was supported by the Engineering and Physical Science Research Council (EPSRC) (Grant number RG63021), UK. J. Albino Aguiar thanks CNPq (307552/2012-8), CAPES (PNPD-230.007518/2011-11) and FACEPE (APQ-0589-1.05/08) for financial support.
Publisher Copyright:
© 2014 Elsevier B.V. All rights reserved.
PY - 2014
Y1 - 2014
N2 - In this work we report the surface morphology of amorphous germanium (a-Ge) thin films (140nm thickness) following thermal outgassing of SiO 2 /Si substrates. The thermal outgassing was performed by annealing the samples in air at different temperatures from 400 to 900°C. Annealing at 400°C in slow (2°C/min) and fast (10°C/min) modes promotes the formation of bubbles on the surface. A cross sectional view by transmission electron microscope taken of the sample slow annealed at 400 °C reveals traces of gas species embedded in the a-Ge film, allowing us to propose a possible mechanism for the formation of the bubbles. The calculated internal pressure and number of gas molecules for this sample are 30MPa and 38 × 10 8 , respectively. Over an area of 22 × 10 -3 cm 2 the density of bubbles obtained at slow annealing (9 × 10 3 cm -2 ) is smaller than that at rapid annealing (6.4 × 10 4 cm -2 ), indicating that the amount of liberated gas in both cases is only a fraction of the total gas contained in the substrate. After increasing the annealing temperature in the slow mode, bubbles of different diameters (from tens of nanometers up to tens of micrometers) randomly distribute over the Ge film and they grow with temperature. Vertical diffusion of the outgas species through the film dominates the annealing temperature interval 400-600 °C, whereas coalescence of bubbles caused by lateral diffusion is detected after annealing at 700 ° C. The bubbles explode after annealing the samples at 800 °C. Annealing at higher temperatures, such as 900 °C, leads to surface migration of the film to the exploded bubbles and eventually forming islands of polycrystalline GeO 2 .
AB - In this work we report the surface morphology of amorphous germanium (a-Ge) thin films (140nm thickness) following thermal outgassing of SiO 2 /Si substrates. The thermal outgassing was performed by annealing the samples in air at different temperatures from 400 to 900°C. Annealing at 400°C in slow (2°C/min) and fast (10°C/min) modes promotes the formation of bubbles on the surface. A cross sectional view by transmission electron microscope taken of the sample slow annealed at 400 °C reveals traces of gas species embedded in the a-Ge film, allowing us to propose a possible mechanism for the formation of the bubbles. The calculated internal pressure and number of gas molecules for this sample are 30MPa and 38 × 10 8 , respectively. Over an area of 22 × 10 -3 cm 2 the density of bubbles obtained at slow annealing (9 × 10 3 cm -2 ) is smaller than that at rapid annealing (6.4 × 10 4 cm -2 ), indicating that the amount of liberated gas in both cases is only a fraction of the total gas contained in the substrate. After increasing the annealing temperature in the slow mode, bubbles of different diameters (from tens of nanometers up to tens of micrometers) randomly distribute over the Ge film and they grow with temperature. Vertical diffusion of the outgas species through the film dominates the annealing temperature interval 400-600 °C, whereas coalescence of bubbles caused by lateral diffusion is detected after annealing at 700 ° C. The bubbles explode after annealing the samples at 800 °C. Annealing at higher temperatures, such as 900 °C, leads to surface migration of the film to the exploded bubbles and eventually forming islands of polycrystalline GeO 2 .
KW - Amorphous germanium
KW - Annealing Ge thin films
KW - Bubbles on ge surfaces
KW - Outgassing of SiO /Si substrates
KW - Surface diffusion of Ge films
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U2 - 10.1016/j.apsusc.2014.07.073
DO - 10.1016/j.apsusc.2014.07.073
M3 - Article
AN - SCOPUS:84922553420
VL - 316
SP - 15
EP - 21
JO - Applied Surface Science
JF - Applied Surface Science
SN - 0169-4332
IS - 1
ER -