RHEED Observation of Tin Atomic Chains Formation on Vicinal Gallium Arsenide Plane
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RHEED Observation of Tin Atomic Chains Formation on Vicinal Gallium Arsenide Plane Aleksey Senichkin, Aleksandr Bugaev, Vladimir Mokerov Institute of Radio Engineering and Electronics of RAS, 103907, 11 Mokchovaia str., Moscow, Russia. ABSTRACT In the present work by means of measurements of RHEED intensity the research of the arrangement of tin atoms on vicinal surfaces of GaAs crystals was carried out. The orientation of crystals was close to (001). The intensity of diffracted electrons was measured in different points of the diffraction picture to reveal the arrangement of tin atoms on terraces or on edges of terraces. It was shown that tin atoms may decorate edges of terraces and thus form chains. Concentrations of tin atoms located on terraces and their edges were established. It was revealed, that tin atoms decorate edges of terraces only at rather high temperatures of a substrate. INTRODUCTION It is known, that delta – doped by Sn GaAs structures grown on substrates inclined from the exact orientation {001} by rotation around the direction exhibit anisotropy of the electrical conductivity in directions along and across edges of terraces of the vicinal surface [1]. The anisotropy of the electrical conductivity in the delta - doped layer of a cubic crystal forces the assumption that the distribution of the impurity in the doped layer is not uniform. To study the arrangement of atoms of tin on such a vicinal GaAs surface, the present work was made. Reflected high energy electron diffraction (RHEED) was used as a method of research allowing to judge about an arrangement of doping atoms on a surface of a crystal. It is well known that this method allows derivation of the information about the structure of some upper monolayers of a crystalline surface if the primary electron beam has a small (about 1 - 2o ) angle with the investigated surface. Results of RHEED intensity measurements at these small angles may be interpreted in the framework of the kinematical theory of diffraction. Sn atoms have essential (~ 40 %) distinction of atomic amplitudes of electron scattering in comparison with Ga atoms [2]. Estimation shows that it is possible to register changes of reflected electrons on a diffraction picture if delta – doping levels have the magnitude 10 12 – 10 13 cm –2 , i.e., at a level of 0.1 - 1.0 % of a monolayer. EXPERIMENTAL DETAILS A molecular beam epitaxy system MBE-500 (“RIBER”, France) was used to make this work. This system is equipped with a RHEED and with an Auger - spectrometer to carry out research on structure and composition of a surface. Substrates were GaAs semi-insulating crystals inclined from the exact orientation (001) on 3 o by rotation around the direction [1-10]. GaAs layers having thickness about 1 micron were grown before delta – doping. The growth conditions corresponded to usual layer-by-layer crystal growth mode with sharp oscillations of the intensity of the electron specular beam. After the end of a film growth the substrate temperature was varied and small amounts of GaAs (about a fe
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