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5241. GaAs-oxide interface states: Gigantic photoionization via Augerlike process
Classified abstracts 5237-5245 37 5237. The surface energy of Si, GaAs, and GaP. (USA) The surface energy of various planes in Si, OaAs, and G a P was measured by the use of a modified spark discharge method, previously used successfully in metals. Surface energy values were determined for the following cleavage planes in these crystals: Si ]111', ~ 1.14 J m 2, Si [ 110~l ~ 1.9 J m 2, GaAs ', 110 ~, ~ 0.86 J m "~,and G a P I 110 ~, ~ 1.9 J rn 2. The Si surface energy value was compared with previous experimental measurements. The Si :110 ~. GaAs ~110~,, and G a P ~110 ~, values were compared only to theoretical estimations, since as far as it is known, the surface energy of these planes have never been measured experimentally. BergBarrett X-ray topography and chemical etch pit analysis verified that plastic relaxation did not occur under the test conditions used. The cleavage surface energies determined in this work were in good agreement with previous theoretical estimations. Experimental observations confirmed a lack of plastic energy dissipation and a stability of cleavage propagation which indicated that the measured surface energies were close to the intrinsic values. C Messmer and J C Bilello, d AppI Phys, 52 (7), 1981. 4623 4629. 37 5238. A study of the Si-Au-Ag interface by surface techniques. IUSA) Auger spectroscopy, electron energy loss spectroscopy, and ion depth profiling techniques, under uhv conditions, have been applied to the study of the formation of the Si-Au-Ag interface. The results show that the presence ofgold atoms on the ( I 11 ) face of a silicon substrate modifies drastically the structure of the silver layer subsequentl.~ deposited. At room temperature, from the Si substrate, one finds successively (i) a diffuse zone composed of an Si-Au-Ag alloy, the Ag concentration of which increases progressively (both gold-sih, er intermixing and silicon atoms diffusion from the bulk contribute to its formation I. (ii) a pure silver layer, and (iiil a surface layer where silicon atoms have segregated and formed an Ag-Si alloy. The influence of the predeposited gold layer thickness has been investigated. Similar interface structures are obtained with gold coverage as low as 1.5 monolayers. These peculiar properties must be contrasted with the Si-Ag abrupt interface case where no silicon diffusion takes place. Results can be explained within a qualitative model involving interstitial diffusion of gold. The annealing of a room-temperature-grown interface shows two distinct regimes: for temperatures <400:C, both silicon diffusion and gold-silver intermixing are enhanced. Beyond 4 0 0 C, agglomeration of the metal overlayers takes place. (France) A Cros et al, J Appl Phys. 52 171, 1981, 4757 4768. 37 5239. Ion channeling and Auger electron spectroscopystudy of Sb-diffused P b ~ . , SnxTe crystals. (USA) An experimental study has been made of the effect of Sb diffusion on the crystalline quality and surface composition of Pb~ ,Sn,Te single crystals (x~0.13) used in fabricating homojunction diode lasers. Both ion backscattering-channeling and Auger electron spectroscopy have been employed. It is found that the crystalline quality in the bulk improves on diffusion, due to a decrease in dislocation density associated with the diffusion temperature. In the near-surface region the quality deteriorates. due to the production of defects which are probably small clusters associated with Sb. The most pronounced effect is a partial or total loss of Te (and probably Sn) from the native oxide, accompanied by other changes in the oxide composition. A long term growth of a very thick oxide also occurs following diffusion. The changes in the oxide can be related to the formation of a p-type surface layer on diffused crystals exposed to air, through oxygen adsorption. R B Alexander el al, J AppI Phys, 52 17). 1981, 4593 4599. 37 5240. Design of a molecular beam surface scattering apparatus for velocity and angular distribution measurements. (USA) A molecular beam surface scattering apparatus designed for the study of corrosion and catalytic surface reactions is described. The apparatus incorporates two molecular or atomic beams aimed at a surface characterized by low energy electron diffraction ILEED) and Auger electron spectroscopy (AES), a rotatable, differentially pumped quadrupole mass spectrometer, and a versatile manipulator. Angular distributions and energy distributions as a function of angle and independent of the surface residence time can be measured. Typical data for the oxidation of deuterium to D~O on a Pt( 111 ) crystal surface are presented. S T Ceyer et al, J Vac Sci Teclmol, 19 13}, 1981, 726 733.
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37 5241. GaAs-oxide interface states: Gigantic photoionization via Augerlike process. (USA) Spectral and transient responses of photostimulated current in MOS structures were employed for the study of GaAs anodic oxide interface states. Discrete deep traps at 0.7 and 0.85 eV below the conduction band were found with concentrations of 5× 10t2cm 2 and 7× 10 ~ cm z respectively. These traps coincide with interface states induced on clean GaAs surfaces by oxygen and or metal adatoms Isubmonolayer coverage). In contrast to surfaces with low oxygen coverage, the GaAs-thick oxide interfaces exhibited a high density (about 10 ~" cm ~) of shallow donors and acceptors. Photoexcitation of these donor acceptor pairs led to a gigantic photoionization of deep interface states with rates 103 times greater than direct transitions into the conduction band. The gigantic photoionization is explained on the basis of energy transfer from excited donor-acceptor pairs to deep states. J Lagowski et al, J Vac Sci Teclmol, 19 13), 1981, 519 524. 37 5242. Surface topography and alignment of liquid crystals on rubbed oxide surfaces. (USA) For several nematic liquid crystals I LC's), the relation between alignments of the LC's on rubbed oxide surfaces and rubbing pressures of the substrates is given. When the LC's take a parallel alignment to the surfaces, good homogeneous alignment is achieved at low pressures. High pressure rubbing also produces good homogeneous alignment of LC's, although alignment is perpendicular to the nonrubbed surfaces. Fine stripes of deposited cloth fibres can be observed on the cloth-rubbed oxide surfaces. The stripes consist of asymmetric projections ranging in the rubbed direction. On the basis of the asymmetric structure formed on the surface, the tilt direction of LC's and their tilt angles are interpreted. Minoru Nakamura, J Appl Ph)'.~, 52 17), 1981, 4561 4567. 37 5243. An atom probe study of the anomalous field evaporation of alloys containing silicon. (USA) In some atom probe microanalytical investigations of homogeneous alloys, the apparent concentrations ofcertain elements have been found to differ from the expected values. Both the time of flight atom probe and the imaging atom probe have been used to study this phenomenon in detail, in the case of an iron 3 wt°,, silicon transformer steel. The apparent concentration of silicon is found to depend on pulse fraction, time between pulses, specimen temperature, and crystallographic area. Low pulse fractions and long periods between pulses both give apparent increases in the silicon level. When the probe aperture is positioned inside the central ring ofa (110) pole, the silicon atoms are found to be retained until the end of the evaporation of that layer, and the overall apparent level of silicon is approximately three times higher than expected. These results suggest that certain elements may be preferentially removed from an alloy by dc field evaporation during the interval between the HT pulses if incorrect experimental conditions are used. For quantitative atom probe analysis of silicon-containing alloys, it appears that a pulse fraction of at least 15",, is required and that analysis inside the central ring of low index poles should be avoided. (GB) M K Miller and G D W Smith, J Vac Sci Teclmol, 19 11), 1981, 574~2. 37 5244. Surface reconstruction and interface formation in Si and GaAs. IUSAI We investigated the effects of substrate surface reconstruction upon the interface formation between In and Ge overla)ers and Sill l 1)2 x 1. Si( 111 )7 x 7, and GaAsi 110) substrates. Photoemission spectroscopy with synchroton radiation was used to monitor the evolution of the interface parameters Schottky barrier height or band discontinuities as a function of the overlayer thickness. All interfaces in~ol~ing Si( 111 )7 x 7 substrates exhibited a characteristic evolution pattern with saturation at 1.4 1.8 monolayers coverage. The interfaces involving Si(lll)2 x I substrates instead exhibited faster evolution saturating below a monolayer coverage with marked differences between individual cleaved surfaces. A similarl.~ rapid evolution ~ a s observed for the interfaces involving GaAs(110) substratcs. These results indicate that the spectrum of intrinsic surface states is different for Sil I 11 )2 × I and for Si(I 11 )7 x 7. In particular for Sill I 1 )7 x 7 a large density of localized states exists near the Fermi level. A D Katnani et al, J Vac Sci Teclmol, 19 (3), 1981, 290-293. 37 5245. Atomic structure of GaP (I 10) and (I I I) faces. (USA) Low energy electron diffraction (LEED)intensities have been measured
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37 5241. GaAs-oxide interface states: Gigantic photoionization via Augerlike process. (USA) Spectral and transient responses of photostimulated current in MOS structures were employed for the study of GaAs anodic oxide interface states. Discrete deep traps at 0.7 and 0.85 eV below the conduction band were found with concentrations of 5× 10t2cm 2 and 7× 10 ~ cm z respectively. These traps coincide with interface states induced on clean GaAs surfaces by oxygen and or metal adatoms Isubmonolayer coverage). In contrast to surfaces with low oxygen coverage, the GaAs-thick oxide interfaces exhibited a high density (about 10 ~" cm ~) of shallow donors and acceptors. Photoexcitation of these donor acceptor pairs led to a gigantic photoionization of deep interface states with rates 103 times greater than direct transitions into the conduction band. The gigantic photoionization is explained on the basis of energy transfer from excited donor-acceptor pairs to deep states. J Lagowski et al, J Vac Sci Teclmol, 19 13), 1981, 519 524. 37 5242. Surface topography and alignment of liquid crystals on rubbed oxide surfaces. (USA) For several nematic liquid crystals I LC's), the relation between alignments of the LC's on rubbed oxide surfaces and rubbing pressures of the substrates is given. When the LC's take a parallel alignment to the surfaces, good homogeneous alignment is achieved at low pressures. High pressure rubbing also produces good homogeneous alignment of LC's, although alignment is perpendicular to the nonrubbed surfaces. Fine stripes of deposited cloth fibres can be observed on the cloth-rubbed oxide surfaces. The stripes consist of asymmetric projections ranging in the rubbed direction. On the basis of the asymmetric structure formed on the surface, the tilt direction of LC's and their tilt angles are interpreted. Minoru Nakamura, J Appl Ph)'.~, 52 17), 1981, 4561 4567. 37 5243. An atom probe study of the anomalous field evaporation of alloys containing silicon. (USA) In some atom probe microanalytical investigations of homogeneous alloys, the apparent concentrations ofcertain elements have been found to differ from the expected values. Both the time of flight atom probe and the imaging atom probe have been used to study this phenomenon in detail, in the case of an iron 3 wt°,, silicon transformer steel. The apparent concentration of silicon is found to depend on pulse fraction, time between pulses, specimen temperature, and crystallographic area. Low pulse fractions and long periods between pulses both give apparent increases in the silicon level. When the probe aperture is positioned inside the central ring ofa (110) pole, the silicon atoms are found to be retained until the end of the evaporation of that layer, and the overall apparent level of silicon is approximately three times higher than expected. These results suggest that certain elements may be preferentially removed from an alloy by dc field evaporation during the interval between the HT pulses if incorrect experimental conditions are used. For quantitative atom probe analysis of silicon-containing alloys, it appears that a pulse fraction of at least 15",, is required and that analysis inside the central ring of low index poles should be avoided. (GB) M K Miller and G D W Smith, J Vac Sci Teclmol, 19 11), 1981, 574~2. 37 5244. Surface reconstruction and interface formation in Si and GaAs. IUSAI We investigated the effects of substrate surface reconstruction upon the interface formation between In and Ge overla)ers and Sill l 1)2 x 1. Si( 111 )7 x 7, and GaAsi 110) substrates. Photoemission spectroscopy with synchroton radiation was used to monitor the evolution of the interface parameters Schottky barrier height or band discontinuities as a function of the overlayer thickness. All interfaces in~ol~ing Si( 111 )7 x 7 substrates exhibited a characteristic evolution pattern with saturation at 1.4 1.8 monolayers coverage. The interfaces involving Si(lll)2 x I substrates instead exhibited faster evolution saturating below a monolayer coverage with marked differences between individual cleaved surfaces. A similarl.~ rapid evolution ~ a s observed for the interfaces involving GaAs(110) substratcs. These results indicate that the spectrum of intrinsic surface states is different for Sil I 11 )2 × I and for Si(I 11 )7 x 7. In particular for Sill I 1 )7 x 7 a large density of localized states exists near the Fermi level. A D Katnani et al, J Vac Sci Teclmol, 19 (3), 1981, 290-293. 37 5245. Atomic structure of GaP (I 10) and (I I I) faces. (USA) Low energy electron diffraction (LEED)intensities have been measured