Ab initio study of Ge Adsorption on H-terminated Si(001) Surfaces
- PDF / 150,044 Bytes
- 6 Pages / 595 x 842 pts (A4) Page_size
- 94 Downloads / 206 Views
Ab initio study of Ge Adsorption on H-terminated Si(001) Surfaces Takahisa Ohno1, 2, Jun Nara1 and Takahide Ezaki2 1 National Research Institute for Metals, 1-2-1 Sengen, Tsukuba-shi, Ibaraki 305-0047, JAPAN 2 Science University of Tokyo, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, JAPAN ABSTRACT The Ge adsorption and diffusion processes on the monohydride terminated Si(001) surface are investigated by using first-principles total-energy calculations and kinetic Monte Carlo simulations. We find that the adsorbed Ge atoms tend to exchange sites with substrate Si dimer atoms. The site exchange plays an important role, which provides the most stable geometry and the easiest diffusion pathway. The Ge adatom migrates in the subsurface region instead of on the surface. The temporal variation in the adsorption geometry during diffusion is found. The Si atoms can become the surface diffusion species instead of the Ge atoms, as a result of the site exchange.
INTRODUCTION The Ge1-xSix/Si heterostructure system has attracted considerable interest because of not only the technological importance such as optoelectronic applications but also the scientific interest. Ge1-xSix growth on a clean Si(001) surface has some undesirable features: a large interface mixing and a rough surface due to the Stranski-Krastanow ( SK ) growth in which a layer-by-layer growth mode is followed by the three dimensional ( 3D ) islanding. Surface hydrogen is known to act as the surfactant for this system, changing the growth mode from the SK growth to a layer-by-layer growth and preventing the interface mixing of Ge and Si [1,2]. Although much effort has been devoted to Ge growth a on H/Si(001) surface, there are few reports about the effect of the hydrogen termination from the microscopic point of view. Kahng et al. reported the result of STM experiments about Ge adsorption on a H/Si(001) surface, showing an increase of the adsorption sites, lowered diffusivity and the disappearance of the diffusion anisotropy [2]. They claimed that their results are in good agreement with the theoretical investigation. But the theoretical investigation is about the Si adsorption [3]. There is no report about the Ge adsorption. In this paper, we theoretically investigate the adsorption and diffusion of Ge atoms on the H/Si(001)-(2x1) surface by using first-principles total-energy calculation techniques and kinetic Monte Carlo ( kMC ) simulation. It is found that the Ge adatom tends to exchange sites with the substrate dimer Si atom due to the low activation energy and the stable exchange geometry. The site exchange has important effects on the surface kinetics. As a result of the site exchange, the Ge atom forms the most stable geometry and diffuses in the subsurface region. We find that the energy barrier for this Ge adatom diffusion is larger than that on the bare Si(001) surface [4]. It is suggested that the reduction of the surface Ge mobility results in the large density of nucleation centers, leading to a layer-by-layer growth.
P11.3.1
CALCULATION ME
Data Loading...
