Mechanism of structural changes of Si(111) surfaces subjected to low-energy ion pulses during molecular-beam epitaxy |
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Authors: | A V Dvurechenskii V A Zinov’ev V A Markov |
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Institution: | (1) Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russia |
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Abstract: | Reflected high-energy electron diffraction (RHEED) and detection of the intensity oscillations of the specular reflection
have been used to investigate morphological changes in Si(111) associated with the two-dimensional layer-by-layer mechanism
of silicon growth from a molecular beam under conditions of pulsed (0.25–1 s) bombardment with low-energy (80–150 eV) Kr ions
in the interval of small total radiative fluxes (1011–1012 cm22), for which the density of radiation-generated defects is small in comparison with the surface density of the atoms. After
pulsed ion bombardment an increase in the intensity of the specular reflection is observed if the degree of filling of the
monolayer satisfies 0.5<θ<1. No increase in the intensity occurs during the initial stages of filling of the monolayer. The maximum amplitude increment
of the oscillations is reached at θ≈0.8. The magnitude of the amplitude increment of the RHEED oscillations increases with temperature up to 400°C and then falls.
At temperatures above 500°C amplification of the reflection intensity essentially vanishes. Experiments on multiple ion bombardment
of each growing layer showed that the magnitude of the amplitude increment of the oscillations decreased as a function of
the number of deposited layers (the order of the RHEED oscillation). A mechanism for the observed phenomena is proposed, based
on the concept of surface reconstruction by pulsed ion bombardment accompanied by formation of a (7×7) superstructure, which
corresponds to a decrease of the activation energy of surface diffusion of the adatoms. Within the framework of the proposed
mechanism the results of Monte Carlo modeling agree with the main experimental data.
Zh. éksp. Teor. Fiz. 114, 2055–2064 (December 1998) |
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