Epitaxial Growth and Electrical Properties of Thick SmSi 2 Layers on (001) Silicon Franck Natali  , Natalie O. V. Plank, Bart M. Ludbrook, Jan Richter, Thom Minnee, Ben J. Ruck, H. Joe Trodahl, John V. Kennedy 1 , and Lionel Hirsch 2 The MacDiarmid Institute for Advanced Materials and Nanotechnology, School of Chemical and Physical Sciences, Victoria University, P.O. Box 600, Wellington 6140, New Zealand 1 National Isotope Centre, GNS Science, 30 Gracefield Road, P.O. Box 31312, Lower Hutt, New Zealand 2 Laboratory of Integration from Materials to Systems (IMS), UMR CNRS 5218, Site ENSCPB, 16 Av Pey Berland, 33607 Pessac, France Received November 30, 2009; accepted December 7, 2009; published online February 22, 2010 We report on the growth of thick (up to 1.2 mm) epitaxial samarium disilicide layers on (001) oriented silicon substrates. The films have the bulk tetragonal SmSi 2 structure and composition, and grow with a preferential orientation SmSi 2 [100] k Si[110]. A surface reconstruction transition from (11) to (22) appears below 525  C. Transport measurements show an n-type metallic conduction with a room temperature resistivity of 175 m cm decreasing to 85 m cm at 4 K, and a carrier concentration of 1:3  10 22 cm 3 . # 2010 The Japan Society of Applied Physics DOI: 10.1143/JJAP.49.025505 1. Introduction The potential to form silicides, and especially epitaxial silicides, as elements of Si-based integrated circuitry has attracted attention for some decades. The rare earth silicides (RESi) are especially attractive for their metallic nature and their very low Schottky barrier heights of 0.3 – 0.4 eV (0.7 – 0.8 eV) on n-type (p-type) silicon. 1–5) They have application potential for low-resistivity metallic contacts, rectifier diodes, and infrared detectors. 3,4,6) More recently their propensity to form nanostructures 7–9) and their promise for a new generation of interconnects and contacts in very large scale Si-based integrated circuits 10,11) has sparked renewed interest in RESi films. Previous studies of epitaxial RESi utilized mainly (111) oriented silicon substrates, where the films grow with ordered Si vacancies to form RE 3 Si 5 (RESi 1:7 ) with an hexagonal AlB 2 structure, encouraged by the 6-fold sym- metry and close lattice match between the two structures. 1,4) The growth of Sm on Si(111) in the monolayer range has received particular attention, due to the propensity of Sm to change from divalent to trivalent with increasing cover- age. 12–14) However, with the aim of integrating RESi in the mainstream of silicon based micro-electronics, the Si(001) oriented substrate is preferred. Several papers have focussed recently on the formation of hexagonal RESi self-assembled nanostructures on Si(001), 7,9,15) including observations that the formation of Sm 3 Si 5 nanowires or three dimensional (3D) islands with the hexagonal bulk structure is controlled by the substrate vicinality. 8,16) However, only limited attention has been devoted to the epitaxial growth of thick RESi layers on this face, 5,17–21) and there appear to be no reports of the growth of bulk samarium-silicide layers on Si(001). Here we report the growth, structure, and electrical properties of especially high-quality epitaxial SmSi 2 layers up to 1.2 mm thick, prepared by evaporating the samarium directly onto hot silicon (001) substrates, so-called reactive deposition epitaxy. 2. Results and Analysis The experiments were performed on nominal 0:5  Si(001) substrates in a Thermionics ultrahigh vacuum system (<10 8 Torr). Sm metal was evaporated from a tungsten wire basket, and the evaporation rate monitored by a quartz- crystal thickness monitor. The layer thickness was verified by scanning electron microscopy and Rutherford back- scattering spectrometry (RBS). The substrates were prepared by thermal outgassing at 600  C for 2 h in the growth chamber, and then the native oxide was removed by annealing at 950  C. Reflection high-energy electron diffraction (RHEED) along the [110] Si azimuth showed the appearance of the (21) surface reconstruction corre- sponding to monoatomic steps [Fig. 1(a)], indicating clean and well-ordered surfaces. The growth temperature and rate were adjusted to optimise the rapid two-dimensional (2D) growth mode of the SmSi 2 layer, achieved with a temper- ature above 500  C, and a Sm evaporation rate less than 0.2 nm/s. All of the films described here were grown under these conditions. The RHEED pattern evolution during the direct growth on Si indicated that an initial 3D growth mode progressively becomes 2D after 10 – 20 nm. Figure 1(b) shows the RHEED pattern observed after the formation Fig. 1. (Color online) RHEED pattern evolution along the Si[110] azimuth: (a) clean Si(001) surface showing a (21) surface reconstruc- tion prior to deposition, (b) after 50 nm, and (c) after 250 nm of SmSi 2 . (d) Evolution of lattice parameter as a function of time during the early growth stages.  E-mail: franck.natali@vuw.ac.nz Japanese Journal of Applied Physics 49 (2010) 025505 REGULAR PAPER 025505-1 # 2010 The Japan Society of Applied Physics