A. U. Mac Rae

Adsorption of oxygen on the {111}, {100} and {110} surfaces of clean nickel

Abstract A study of the adsorption of oxygen on the clean (111), (001) and (110) surfaces of nickel, using low energy electron diffraction techniques, reveals that several structures form on each of these surfaces before a monolayer oxygen coverage is attained. These structures are composed of both oxygen and nickel atoms in the topmost layer. Each structure is characterized by a sticking probability, work function change, oxygen coverage, and degradation temperature. The oxygen is adsorbed via a different mechanism on each of these surfaces. An order-disorder type of transition is observed when the temperature of a (111) oriented crystal, containing a quarter of a monolayer of oxygen, is increased to 160 °C. The close similarity of the structures to three-dimensional nickel oxide, and the magnitude of the work function changes, indicates that the surface oxygen-nickel bond is quite ionic in nature.

Low energy electron diffraction study of the polar {111} surfaces of GaAs and GaSb

Abstract Low energy electron diffraction patterns were obtained from the polar {111} surfaces of GaAs and GaSb following argon ion bombardment and annealing at 450 °C and 400 °C respectively. Patterns characteristic of a (2 × 2) structure were obtained from the (111)A surfaces and a (3 × 3) structure from the (111)B surfaces of both materials, indicating surface reconstruction. Heating GaAs above 600 °C and GaSb above 550 °C resulted in the formation of facets having {110} sides on the surface. The A surfaces are much more stable than the B as evidenced by the ease in obtaining patterns from the A surface by annealing the ion bombarded surfaces, the rapid formation of the facets on the B surface by heating, the deterioration of the (3 × 3) structure patterns due to interaction with the residual gas in the vacuum system and a sticking probability for oxygen that was ten times greater for the (111)As surface than the (111)Ga surface. Diffraction patterns characteristic of clean surfaces were obtained following a high temperature heating that produced a film of Ga on the surfaces. This vividly illustrates that while the existence of a clean surface pattern is a necessary condition, it is not a sufficient condition for the establishment of a clean surface.

Low‐Energy Electron‐Diffraction Study of the Cleaved (110) Surfaces of InSb, InAs, GaAs, and GaSb

The (110) surfaces of InSb, InAs, GaSb, and GaAs produced by the Gobeli‐Allen cleavage technique, have been studied by low‐energy electron diffraction. The unit mesh at this surface of these III‐V compounds has the same dimensions as the substrate unit mesh. A strong asymmetry in the intensity of the hk and hk diffraction beams reveals that the surface atoms preferentially shield the atoms in the second layer and that the arrangement of atoms at the surface is not the same as the arrangement of atoms in the bulk of the crystal. No change in the surface structures was observed by heating the crystals close to their melting points following the cleavage. These same structures could also be produced by argon ion bombardment and anneal. The sticking probability for oxygen on the (110) surface was established to be less than 10−5 for all of the materials investigated.

An electron diffraction study of cesium adsorption on tungsten

Abstract Surface structures, work function changes, Auger electron losses and surface plasma losses have been studied for the adsorption of cesium on clean surfaces of tungsten. The first structures observed to form on both the (100) and (110) surfaces are due to the adsorption of cesium in an ionic form, while the last structures are due to a second layer of metallic cesium. This last structurre is the same for both surfaces, being a hexagonal close-packed arrangement of cesium atoms. That this structure on the (100) surface is metallic is evidenced by the observation of a cesium surface plasmon peak that increases in intensity as the hexagonal array is formed. The work function minimum is characterized by a definite two-dimensional structure.

The isothermal annealing of boron implanted silicon

Abstract Isothermal annealing studies of boron implanted silicon have been made at temperatures above 600°C for boron doses in the range of 1014 to 1015 ions/cm2. A 5 eV activation energy is obtained in the temperature range 600°C to 900°C. This value is the same as that associated with the generation and subsequent migration of vacancies in silicon. This indicates that the mechanism responsible for the increase in electrical activity of the implanted boron is due to the thermal generation of vacancies and the diffusion of these vacancies or vacancy complexes to interstitial boron atoms, which then become substitutional. The characteristic annealing times are dose dependent. No simple integral-order kinetic process will explain all the data. Good agreement between the data and a calculation is obtained if it is assumed that the characteristic annealing times are position dependent. Detailed data are presented which provide the time and temperature necessary to obtain complete electrical activity of boron ...

Low‐Energy Electron Diffraction Study of the Cleaved Surfaces of PbS, PbSe, and PbTe

Low‐energy electron diffraction was used to study the cleaved surfaces of PbS, PbSe, and PbTe for the purpose of obtaining information about the factors that influence the intensities of the diffracted beams. The addition of the successively heavier anion in the three compounds produced no significant changes in the intensities that could be attributed to the atomic scattering factors of the anions. Prominent features in the dependence of the intensity of the diffracted beams on the energy of the incident electrons are attributed to multiple scattering. The structure of the surfaces in two dimensions parallel to the surface is the same as the (001) substrate planes. A complete analysis of structure normal to the surface is prevented by strong multiple scattering. Single scattering events are identified at low energies by measurements on the angular dependence of the intensities.

Ion implantation for junction field effect transistors compatible with integrated circuits

The ability to use junction field effect transistors in integrated circuits simplifies circuit design. This paper describes the techniques used in fabricating p-channel junction field effect transistors (J-FET) in an integrated circuit, using ion implantation and standard IC processing. This circuit contains resistors, transistors and three J-FETs on the same chip. The J-FETs are used as constant current sources and have a pinch-off voltage of less than 2 volts and an I DSS of ∼ 1 ma. The J-FETs are formed by ion implanting 5 × 1012/cm2B+at 100 keV, using SiO 2 as a mask to define the p-region which eventually becomes the channel region. The n-type gate is formed at the same time as the emitters of the transistors. The resultant circuits are characterized by a uniform J-FET pinch-off voltage and I DSS , reflecting the control associated with ion implantation.

RECENT ADVANCES IN ION IMPLANTED JUNCTION-DEVICE TECHNOLOGY.

Recent applications of ion implantation to the fabrication of silicon discrete and integrated circuits indicates that this process may be used successfully in each step involving doping of the silicon. Techniques have been developed to fabricate the diode array for PICTUREPHONE®; room temperature double implanted, high gain transistors, and buried layers for integrated circuits. The successful fabrication of these structures overcomes some previously considered limitations of the ion implantation process.

Novel applications of ion implantation to LSI processing

Ion implantation has been successfully utilized to simplify the fabrication of a 1024 bit IGFET random access memory array ina novel manner. IGFET integrated circuits Often require enhanced surface doping to suppress unwanted spurious channels between devices. Using conventional diffusion technology, an extra masking level is required to form these regions. A technique has been developed which eliminates this extra mask by uniformly increasing the doping in the surface layer of the silicon and then controllably compensating the enchanced doping in the windows patterned to form gate oxide regions. Threshold voltage control is excellent, mobilities are normal and no undesirable effects have been observed if care is exercised in controlling the implanted doses.