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n-GaAs contacts
Classified abstracts 33983407 permeates helium contained in analysed probes. It is found that the coefficient of trapping He ions in the pump is 0.76 f 30% and it does not deoend on discharge voltage in the range 0.9 to 3.3 kV. The life of the indicator is lo4 &alysesat a sensitivity of 5 x 10-r” A/torr. V V Pimenov, Prib Tekh Eksper, No 2, 1975, 250-251 (in Russion).
III.
Vacuum
30. EVAPORATION
applications AND
DEPOSITION
IN VACUO
30 3398. Epitaxial growth of Ag films on InP (001) by atomic beam epitaxy in ultra-high vacuum. (GB) The epitaxial growth of smooth, continuous Ag films on clean, characterized InP (001) surfaces at ~40°C has been achieved by atomic beam epitaxy in ultra-high vacuum. Epitaxy on the P-stabilized, (OO’l)-C (2 x 8) reconstructed surface has been observed. The observed epitaxial relationship is consistent with published work on epitaxy of FCC metals on III-V compound semiconductors. Electrical measurements on the epitaxial Ag-InP contacts show that they are ohmic at 77 and 300 K. RFFarrow,JPhys D: ApplPhys, lO(lO), 1977, L135-L138. 30 3399. An X-ray diffraction profile study in silver tllms vapour-deposited on a rotating substrate with the axial centre at 44” to the vapour direction. (GB) A detailed X-ray diffraction profile analysis on silver films (thickness -32-248 nm), vapour-deposited on a rotating substrate with the axial centre at 44” to the vapour direction, shows the presence of small coherent domain sizes (-76-305 A), appreciable microstrains, small lattice parameter change (-3.5-2.0 x lOwa for films < 100 nm thick), residual compressive stress (u - 0.05-0.003 x lo-r0 N m-z), appreciable growth or twin stacking fault concentration (fi - 11525 x 10-s) and large dislocation density (-8-1 x 10” cm-‘). The effects decrease with increasing film thickness and are comparable or slightly reduced in magnitude relative to the case for normal vapour incidence. The films, which were initially random, develop {ill } orientation at higher thickness. (India) S Sen et al,JPhys D: ApplPhys, 10 (IO), 1977, L139-L142. 30 3400. Residual stress measurements in hexagonal zinc films from X-ray peak shift analysis. (GB) An expression has been derived, in the light of X-ray peak-shift analysis of cubic structures by Wagner, to estimate the average residual internal stresses and lattice parameter changes in hexagonal systems from measurements of relative peak-position displacements in a powder difiractometer. This has been applied to several vacuumevaporated zinc films (-20-500 nm thick), prepared at room temperature (25°C) at a residual air pressure -5 x 10v5 torr from a normal source. Considering the first four reflections, namely 00.2, 10.0, 10.1 and 10.2, present analysis shows that the films exhibit appreciable residual internal stresses D (tensile) lying in the range 1.185-0.569 x log N m-* (-17 to 8 x lo4 osi). which decrease gradually with increasing thickness. The thermaistr&es being small, residual internal stresses appear to be mostly due to the intrinsic stresses originating from lattice imperfections in the films. The lattice parameter changes (Au, AC) are relatively small, and close to the experimental error limits. (India) R K Nandi and S P Sen Gupta, J Phys D: Appl Phys, 10 (I l), 1977, 1479-1485. 30 3401. In situ determination of tbe optical and electrical properties of thin 8lms during their deposition. (GB) We describe an experimental arrangement for measuring in situ in a nearly continuous way the reflectance R and transmittance T near normal incidence, as well as the electrical dc resistance of thin films throughout their deposition and subsequent heat treatments. It is then possible to determine the effective complex dielectric constant ‘E and the electrical dc resistivity p as functions of the mass thickness of the deposit and to follow their evolution during film growth. The possibilities of the method are demonstrated by an application to thin films of gold. (France) P Gademre and G Vuye, J Phys E: Scient Instrum, 10 (7), 1977, 733736. 100
30 3492. Evidence for a superlattice at SiSiO, interface. (USA) Evidence is presented for periodic structure at the Si-SiO, interface in MOSFET’s in which the interface is a vicinal-plane of (100). The results are discussed in terms of their relevance to interface technology. (Germany) P J Stiles et al, J Vat Sci Technol, 14 (4), 1977,969-972. 30 3403. Effect of a glassy membrane on the Scbottky barrier between silicon and metallic silicidea. (USA) We present a model for Schottky barriers on silicon based upon the formation of a glassy membrane layer between the last metal layer and silicon. We postulate that this membrane has the properties of a semiconducting glass with quasiparticle states in the gap, characterized by a negative correlation energy. These states effectively pin the Fermi level with respect to the silicon bands at a level depending on the silicon-metal molecular bonding in the membrane layer. This model thus gives a physical picture for Fermi-level pinning which agrees semiquantitatively with Schottky barrier measurements. R W Ben& and R M Waiver, J Vuc Sci Technol, 14 (4), 1977,925-929. 30 3484. Electrical properties of anodic and pyrolytic dielectrics on gallium arsenide. (USA) Capacitancsvoltage and current-voltage measurements have been used to characterize dielectrics grown by anodization and by pyrolytic deposition on bulk n-type gallium arsenide. The anodic oxide is an ohmic insulator with a resistivity 210L6 ohm cm and a breakdown field of 3 x lo6 V/cm. Pyrolytically deposited SixOYN, films exhibited resistivities of 1OL5ohm cm and breakdown fields between 5 x lOsand 1 x 10’ V/cm. C-V data for the anodic and pyrolytic dielectrics are very similar, implying in each case: a fixed charge of more than lOI* electrons/cm2 in the dielectric, temporary trapping and release of 2-3 x 1O’O electrons/cm2 at the semiconductor-dielectric interface for each volt of applied bias, and a U-shaped density of surface states in the upper half gap with a minimum value of 2-4 x 10” cmm2 eV-’ C R Zeisse et al, J Vat Sci Technol, 14 (4), 1977,957-960. 30 3495. Interdiffusion and Scbottky-barrier-height variations in Au-W(Ti)/n-GaAs contacts. (USA) Au-W(Ti)/n-GaAs diodes were constructed for the purpose of examining the thermal stability of the metal-GaAs interface and the integrity of the W(D) diffusion barrier. The evaluation procedure consisted of using measurements of the Schottky barrier height and other electrical parameters as a function of annealing temperatures. Barrier heights, Vb(lO), determined by measurement of the zero voltage current intercept, f,, were found to increase with annealing temperatures up to 600°C. Values determined by the measurement of forward current activation energies were in agreement with Vb(13 up to 500°C. Above 5OC”C, however, this method was not applicable, due to the onset of excess forward current at low voltages. This current was accompanied by evidence of gold interdiffusion, compensation and high electric field strength in the depletion layer. Direct identification of the excess current source, however, was not accomplished. H M Day et al, J Vuc Sci Technol, 14 (4), 1977,939-942. 30 3406. Investigation of the Au-Ge-Ni and Au-GePt system used for alloyed contacts to GaAs. (USA) Widely used metallization schemes for alloyed contacts to n-type GaAs consist of a Au-Ge alloy with a cover layer of Ni or Pt. We have studied the interaction of these elements (Au-Ge and Ni, Au-Ge and Pt) upon heat treatment on an inert substrate. Our results show that Ni and Pt play an active role in contact formation. During heat treatment the Ge diffuses out of the Au into the Ni or Pt layer, respectively, where it forms stable compounds. Due to the fact that Ni and Pt act as a sink for Ge the composition and, as it is shown, the uniformity of the heat-treated layers depend on the ratio of the amount of evaporated Ge to Ni or to Pt. M Wittmer et al, J Vat Sci Technol, 14 (4), 1977, 935-936. 30 3497. Highly electronegative contacts to compound semiconductors. (USA) Gold contacts to most III-V and II-VI compounds position the Fermi level at the interface well into the energy gaps of the semiconductors. To position the Fermi level closer to a conduction-band
III.
Vacuum
30. EVAPORATION
applications AND
DEPOSITION
IN VACUO
30 3398. Epitaxial growth of Ag films on InP (001) by atomic beam epitaxy in ultra-high vacuum. (GB) The epitaxial growth of smooth, continuous Ag films on clean, characterized InP (001) surfaces at ~40°C has been achieved by atomic beam epitaxy in ultra-high vacuum. Epitaxy on the P-stabilized, (OO’l)-C (2 x 8) reconstructed surface has been observed. The observed epitaxial relationship is consistent with published work on epitaxy of FCC metals on III-V compound semiconductors. Electrical measurements on the epitaxial Ag-InP contacts show that they are ohmic at 77 and 300 K. RFFarrow,JPhys D: ApplPhys, lO(lO), 1977, L135-L138. 30 3399. An X-ray diffraction profile study in silver tllms vapour-deposited on a rotating substrate with the axial centre at 44” to the vapour direction. (GB) A detailed X-ray diffraction profile analysis on silver films (thickness -32-248 nm), vapour-deposited on a rotating substrate with the axial centre at 44” to the vapour direction, shows the presence of small coherent domain sizes (-76-305 A), appreciable microstrains, small lattice parameter change (-3.5-2.0 x lOwa for films < 100 nm thick), residual compressive stress (u - 0.05-0.003 x lo-r0 N m-z), appreciable growth or twin stacking fault concentration (fi - 11525 x 10-s) and large dislocation density (-8-1 x 10” cm-‘). The effects decrease with increasing film thickness and are comparable or slightly reduced in magnitude relative to the case for normal vapour incidence. The films, which were initially random, develop {ill } orientation at higher thickness. (India) S Sen et al,JPhys D: ApplPhys, 10 (IO), 1977, L139-L142. 30 3400. Residual stress measurements in hexagonal zinc films from X-ray peak shift analysis. (GB) An expression has been derived, in the light of X-ray peak-shift analysis of cubic structures by Wagner, to estimate the average residual internal stresses and lattice parameter changes in hexagonal systems from measurements of relative peak-position displacements in a powder difiractometer. This has been applied to several vacuumevaporated zinc films (-20-500 nm thick), prepared at room temperature (25°C) at a residual air pressure -5 x 10v5 torr from a normal source. Considering the first four reflections, namely 00.2, 10.0, 10.1 and 10.2, present analysis shows that the films exhibit appreciable residual internal stresses D (tensile) lying in the range 1.185-0.569 x log N m-* (-17 to 8 x lo4 osi). which decrease gradually with increasing thickness. The thermaistr&es being small, residual internal stresses appear to be mostly due to the intrinsic stresses originating from lattice imperfections in the films. The lattice parameter changes (Au, AC) are relatively small, and close to the experimental error limits. (India) R K Nandi and S P Sen Gupta, J Phys D: Appl Phys, 10 (I l), 1977, 1479-1485. 30 3401. In situ determination of tbe optical and electrical properties of thin 8lms during their deposition. (GB) We describe an experimental arrangement for measuring in situ in a nearly continuous way the reflectance R and transmittance T near normal incidence, as well as the electrical dc resistance of thin films throughout their deposition and subsequent heat treatments. It is then possible to determine the effective complex dielectric constant ‘E and the electrical dc resistivity p as functions of the mass thickness of the deposit and to follow their evolution during film growth. The possibilities of the method are demonstrated by an application to thin films of gold. (France) P Gademre and G Vuye, J Phys E: Scient Instrum, 10 (7), 1977, 733736. 100
30 3492. Evidence for a superlattice at SiSiO, interface. (USA) Evidence is presented for periodic structure at the Si-SiO, interface in MOSFET’s in which the interface is a vicinal-plane of (100). The results are discussed in terms of their relevance to interface technology. (Germany) P J Stiles et al, J Vat Sci Technol, 14 (4), 1977,969-972. 30 3403. Effect of a glassy membrane on the Scbottky barrier between silicon and metallic silicidea. (USA) We present a model for Schottky barriers on silicon based upon the formation of a glassy membrane layer between the last metal layer and silicon. We postulate that this membrane has the properties of a semiconducting glass with quasiparticle states in the gap, characterized by a negative correlation energy. These states effectively pin the Fermi level with respect to the silicon bands at a level depending on the silicon-metal molecular bonding in the membrane layer. This model thus gives a physical picture for Fermi-level pinning which agrees semiquantitatively with Schottky barrier measurements. R W Ben& and R M Waiver, J Vuc Sci Technol, 14 (4), 1977,925-929. 30 3484. Electrical properties of anodic and pyrolytic dielectrics on gallium arsenide. (USA) Capacitancsvoltage and current-voltage measurements have been used to characterize dielectrics grown by anodization and by pyrolytic deposition on bulk n-type gallium arsenide. The anodic oxide is an ohmic insulator with a resistivity 210L6 ohm cm and a breakdown field of 3 x lo6 V/cm. Pyrolytically deposited SixOYN, films exhibited resistivities of 1OL5ohm cm and breakdown fields between 5 x lOsand 1 x 10’ V/cm. C-V data for the anodic and pyrolytic dielectrics are very similar, implying in each case: a fixed charge of more than lOI* electrons/cm2 in the dielectric, temporary trapping and release of 2-3 x 1O’O electrons/cm2 at the semiconductor-dielectric interface for each volt of applied bias, and a U-shaped density of surface states in the upper half gap with a minimum value of 2-4 x 10” cmm2 eV-’ C R Zeisse et al, J Vat Sci Technol, 14 (4), 1977,957-960. 30 3495. Interdiffusion and Scbottky-barrier-height variations in Au-W(Ti)/n-GaAs contacts. (USA) Au-W(Ti)/n-GaAs diodes were constructed for the purpose of examining the thermal stability of the metal-GaAs interface and the integrity of the W(D) diffusion barrier. The evaluation procedure consisted of using measurements of the Schottky barrier height and other electrical parameters as a function of annealing temperatures. Barrier heights, Vb(lO), determined by measurement of the zero voltage current intercept, f,, were found to increase with annealing temperatures up to 600°C. Values determined by the measurement of forward current activation energies were in agreement with Vb(13 up to 500°C. Above 5OC”C, however, this method was not applicable, due to the onset of excess forward current at low voltages. This current was accompanied by evidence of gold interdiffusion, compensation and high electric field strength in the depletion layer. Direct identification of the excess current source, however, was not accomplished. H M Day et al, J Vuc Sci Technol, 14 (4), 1977,939-942. 30 3406. Investigation of the Au-Ge-Ni and Au-GePt system used for alloyed contacts to GaAs. (USA) Widely used metallization schemes for alloyed contacts to n-type GaAs consist of a Au-Ge alloy with a cover layer of Ni or Pt. We have studied the interaction of these elements (Au-Ge and Ni, Au-Ge and Pt) upon heat treatment on an inert substrate. Our results show that Ni and Pt play an active role in contact formation. During heat treatment the Ge diffuses out of the Au into the Ni or Pt layer, respectively, where it forms stable compounds. Due to the fact that Ni and Pt act as a sink for Ge the composition and, as it is shown, the uniformity of the heat-treated layers depend on the ratio of the amount of evaporated Ge to Ni or to Pt. M Wittmer et al, J Vat Sci Technol, 14 (4), 1977, 935-936. 30 3497. Highly electronegative contacts to compound semiconductors. (USA) Gold contacts to most III-V and II-VI compounds position the Fermi level at the interface well into the energy gaps of the semiconductors. To position the Fermi level closer to a conduction-band