HRLEED and STM Study of Misoriented Si (100) with and without a Te Overlayer
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In recent years, the growth of high quality thin films became first priority because of the need to miniaturize microelectronics. Among all the substrates, Silicon is the most attractive one not only for its high crystalline properties but also for its availability and low cost in the market. The growth of high quality CdTe on misoriented Si(100) represents a challenging and yet promising project for technological applications ( substrate fror growth of MCT, for x-ray detectors) [1-3]. The misorientation angle plays a key role in the growth quality of CdTe/Si(100); this incited our curiosity to investigate the effect of the misorientation angle on the topography of the surface structure of Si(100). Our main goal is to show the relation between the misorientation angle, the terrace width and the step height distributions. Si(100) with 0= 0.50,1.5',4' and 80 misorientation angles towards [110] and [130] were systematically investigated using HRLEED ( High Resolution Low Energy Electron Diffraction ) and STM (Scanning Tunneling Microscopy).HRLEED provides information in reciprocal space while STM gives real space topographic images of the surface structure. Te was evaporated from a Knudsen cell at a substrate temperature of 200 C. We investigated the effect of coverage and temperature on the Te growth. EXPERIMENT The experiments were performed in a standard UHV-chamber at a base pressure of approximately 10-1° torr. The chamber is equipped with a HRLEED or SPA-LEED [4,5]
353 Mat. Res. Soc. Symp. Proc. Vol. 448 0 1997 Materials Research Society
and an STM [6] system. Prior to introduction to the vacuum chamber, samples receive an ex-situ treatment that is they are first boiled in a NH30H solution to remove organic contaminants then submerged in a dilute HF solution to strip off the native oxides; finally, they are boiled in an HCl solution to grow a thin protective oxide layer which is removed upon annealing .In-situ, samples are annealed at 1100 C' or until bright diffraction spots are observed. Both STM and HRLEED measurements were performed on Si(100) with misorientation angle i5= 0.50, 1.50 and 80 towards the [110] direction and 15= 4 towards the [130] direction. For HRLEED measurements, profiles of the specular beam (along the [011] and [01 1]-) at room temperature for different electron energies were recorded by means of an electrostatic deflecting system that scans the electron beam across the aperture of a channeltron detector [5]. By varying the energy of the incident electrons one changes the interference condition which is described by, S, the scattering phase. S is defined as the phase difference between electrons scattered by first and second layer atoms in multiples of the wavelength: integer values of S correspond to an in-phase scattering condition while half-integer values correspond to an out-phase scattering condition. STM measurements were also performed on the different Si(100) misorientations at room temperature. Te was evaporated from an effusion cell, and the deposition rate was monitored by
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