Surfactant-Mediated Growth of MnSi 1.7 on Si(001)
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Surfactant-Mediated Growth of MnSi1.7 on Si(001) S. Teichert, H. Hortenbach, D. K. Sarkar, G. Beddies, and H.-J. Hinneberg Institute of Physics, Chemnitz University of Technology D-09107 Chemnitz, Germany ABSTRACT The formation of the silicide MnSi1.7 by reactive deposition of Mn onto Si(001) has been studied using Sb as a surfactant. The growth was performed under UHV conditions by simultaneous or consecutive exposure of the Si substrates, held at high temperatures (550°C, 600 °C), to a flux of Sb and Mn atoms. The presence of Sb during the growth strongly increases the island density and changes the crystalline orientation of the MnSi1.7 grains. The morphology and the orientation of the resulting silicide are the same both for the deposition of Mn on a Sb terminated Si(001) surface and for the co-deposition of Mn and Sb on Si(001). A residual Sb coverage close to one monolayer (ML) at the sample surface has been determined for both of the preparation modes at Tsub = 550 °C. The transition from the growth mode without Sb to the surfactant-controlled growth has been studied for Tsub = 600 °C. It has been found that the silicide morphology and orientation strongly depend on the thickness of Sb pre-coverage, which was increased from 0 to about 0.7 ML (1 ML = 6.78⋅1014 atoms cm-2).
INTRODUCTION Surfactant-mediated film growth has drawn extensive attention since the pioneering work of Copel et al. [1,2]. Many studies have been carried out on the Si/Ge system using various surfactants, for example, Sb[1-3] , As[1,2], H [4] or Ga [5]. Much less attention has been paid to surfactant-mediated silicide growth on Si although there are interesting fields of application using surfactants for the growth of epitaxial silicide layers or silicide silicon multilayers. In this paper we report the surfactant-mediated growth of MnSi1.7. The manganese silicides with a composition close to MnSi1.7 (Higher Manganese Silicides = HMS) [6-9] have a tetragonal crystal structure. The HMS (e.g. Mn4Si7 or Mn11Si19) show semiconducting properties and are under discussion for application in thermoelectric devices [10, 11]. In the present study the influence of Sb on the reactive formation of MnSi1.7 by Mn deposition onto Si(001) is investigated.
EXPERIMENTAL DETAILS The p-type 4" Si(001) substrates were exposed at first to a standard RCA clean and then etched in a HF solution immediately before being introduced into the UHV evaporation system (base pressure ≤ 5⋅10-11 Torr). The (2x1) Si(001) reconstruction obtained by RHEED after deposition of a 100 nm Si buffer layer indicates an atomically clean substrate surface before starting the deposition of manganese by electron beam evaporation. For all samples nominally 5 nm Mn was deposited at substrate temperatures Tsub of 550°C or 600°C. According to the known crystal data of HMS [12] the used Mn thickness results in an average silicide thickness of P11.34.1
about 14 nm. The Sb applied as surfactant was evaporated from an effusion cell using an Sb flux of 1.9 ML min-1 while the Mn flux supplied to
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