AVS2001 Session SS1-TuP: Semiconductor Surfaces Poster Session
Tuesday, October 30, 2001 5:30 PM in Room 134/135
Tuesday Afternoon
Time Period TuP Sessions | Topic SS Sessions | Time Periods | Topics | AVS2001 Schedule
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SS1-TuP-3 Reduction of Oxidation Rate during the Initial Stages of the Oxidation of Heavily Phosphorus Doped Silicon in Dry Oxygen
Y. Kamiura, K. Hasegawa, Y. Mizokawa (Osaka Prefecture University, Japan); K. Kawamoto (Denso Co. Ltd., Japan) The oxidation of heavily phosphorus doped Si(100) and polycrystalline Si in RT to 800°C range in dry oxygen was studied by Auger electron spectroscopy(AES). The oxidation rate of the phosphorus doped Si(100) was larger than the P-doped poly-Si for each O2 exposure at RT. Phosphorus segregation didn't take place in RT oxidation of the P-doped Si(100). The Dioxide formation gradually occurred from ca. 500L in thermal oxidation at 650°C in the P-doped Si(100). The reduction of oxidation was found above 5x105L. At the same time, the amount of the phosphorus piled-up at Si/SiO2 interface slightly degreased. The accurate AES measurements of 97 to 137eV range showed that phosphorus slightly oxidized in the initial stage of the oxidation of P-doped Si for each O2 exposure and the phosphorus peak in P2O5 was clearly found at ca. 110eV above 103L. It seemed that the modification of this substance fairly desorbed in UHV and the residual partially held into the Si/SiO2 interface at this temperature. Therefore the oxidation of silicon didn't proceed until about ca. 1x106L. On the other hand, the suppression of oxidation of silicon wasn't caused for P-doped poly-Si, the amount of SiO2 strongly increased above 5x105L. The thermal oxidation behavior at 800 °C was quite different from low temperature results. Oxygen uptake on the silicon surfaces didn't almost take place below 103L for both samples because the volatile SiO molecules were formed and the silicon surfaces were etched away by oxygen atoms. Dioxide formations rapidly took place above 104L, and then a large amount of phosphorus piled up at the interfaces due to the formation of SiO2. The P2O5 was formed through low O2 exposures even at this temperature for both samples. |
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SS1-TuP-5 The Investigation of the Semiconductors Surfaces by Method of the Low Energy Ion Scattering
U. Kutliev, B. Kalandarov (Urgench State University, Uzbekistan) In the present work the scattering processes of 5 keV Ne + ions on the GaP(100) surface under grazing ion bombardment have been investigated by computer simulation in the binary collision approximation. The particle interaction were described by the universal BZL-potential. Elastic and inelastic energy losses of scattered ions were summed along their trajectories. Trajectories of incident ions experienced correlated sliding scattering on discrete atomic chains, in semichannels and channels in the <110>, <-100> directions were traced in several nearest to surface atomic layers. The monoatomic steps of the different length, one atomic layer high on the surface were simulated. Energy, angular and spatial distributions of Ne + ions scattered from stepped GaP(100) surface at different crystal directions were calculated. The computer simulation allowed an investigation of the effect of the atomic steps on the real single crystal surface upon the trajectory features and capture in subsurface channeling and dechallening of the ions being scattered on the surface. It has been shown that the presence of atomic steps on the surface lead to increase of the capture probability of channeling ions in the layers under the steps and to increase of probability of their dechanneling. Character of ions movement under the step (their range, energy losses and dechanneling) is determined both the grazing angle and capture angle under the step. |
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SS1-TuP-6 Femtosecond Time-Resolved Photoemission Study of Two-Dimensional Layered Semiconductor MoS2 Surface
A. Tanaka (Tohoku University, Japan and University of Rochester); N.J. Watkins, Y. Gao (University of Rochester) A femtosecond time-resolved two-photon photoemission study of 2H-MoS2 surface has been carried out in order to investigate in detail the relaxation dynamics of hot electrons in the two-dimensional layered semiconductor. Among the lamellar transition metal dichalcogenides, MoS2 is a semiconductor with an indirect gap of about 1.2 eV. The observed two-photon photoemission spectrum with a photon energy of 3.3 eV exhibits a single feature in the intermediate state energy between 2.1 and 3.3 eV above the valence-band maximum (i.e., between 0.9 and 2.1 eV above the conduction-band minimum). From the detailed time-resolved two-photon photoemission measurements as a function of electron excitation energy, it is found that the inverse relaxation lifetime of hot electrons depends linearly on the excess energy above the conduction-band minimum. This result is in strong contrast to the results based on the Fermi liquid theory, which takes into account the electron-electron scattering as the dominant relaxation process and gives the quadratic energy dependent lifetime in the both three- and two-dimensional electron systems within logarithmic corrections. From these results, we discuss the relaxation process of hot electrons in the two-dimensional layered semiconductor. |