We have investigated electrical transport in thin films of CoSi2 at low temperatures as a function of film thickness and observe in conductivity a size effect much smaller than seen heretofore indicative of a high degree of specularity in the boundary scattering. This in large part owes to the unique characteristics of these films, i.e., they are single crystal and continuous down to ∼60Å thickness with long bulk scattering lengths (≈1000Å) in transport at liquid He temperatures and have nearly atomically perfect interfaces.

Epitaxial NiSi2 films of less than 40 Å thickness have been grown on atomically clean Si(111) surfaces. Ion channeling and blocking have been used to determine the morphology and orientation of these films, as well as the strain resulting from the lattice mismatch with the Si substrate. The films are found to be continuous for Ni coverages above 5×1015 atoms/cm2. For all coverages the films are (111) oriented but rotated 180° around the surface normal with respect to the substrate. The NiSi2-Si(111) interface has been probed directly by the ion beam and is found to be well ordered and atomically abrupt.

The lattice mismatch of single-crystal epitaxial nickel disilicide of orientation A and B on Si(111) has been measured in and out of the <111> growth direction using a four-circle X-ray diffractometer. In both directions the mismatch of the as-grown B-type film was found to be larger than for the A-type; after annealing at 800°C the mismatch of the A-type approached the value of the B-type, while the latter remained the same. This result suggests that the B-type NiSi2 film has relaxed more during growth than the A-type which can only be relieved by subsequent annealing. This difference in A- and B-type mismatch is correlated with TEM studies. The combined results provide evidence that the growth of either A or B orientation is strongly affected by the nature and density of the misfit dislocations.

Epitaxial refractory silicides were grown on silicon by solid phase epitaxy method. Transmission electron microscopy has been performed to study the microstructures of epitaxial layers and their orientation relationships with respect to substrate Si.

Metal thin films, electron-gun deposited, or sputtered metal-silicon films were annealed in N2 ambient or in vacuum at 200°C-1100°C. Substrate heating, two step annealing and ion beam mixing were applied to induce the growth and improve the quality of epitaxial films. In this paper, formation and structures of epitaxial CrSi2, VSi2, ZrSi2, MoSi2 and WSi2 are presented. Preliminary results of the epitaxial growth of TiSi2, TaSi2 and NbSi2 are reported.

Except for a few special cases, the electrical and optical properties of most III-V semiconductor surfaces and interfaces can be explained in terms of surface Fermi level pinning. However, despite years of research there is no universal agreement on the origin of this pinning. This problem is of more than just academic interest since pinning affects optoelectronic device performance via surface recombination losses, and high speed device performance through uncontrollable ohmic and Schottky contact properties for MESFETs and through a high interface trap density for MISFETs.

This talk reviews some of the approaches to the pinning problem and presents some recent results on the role of misfit dislocations in pinning. In particular it will be shown that there are are several models which can explain the usually observed pinning positions. However, we have developed a modified work function model capable of explaining both the usual pinning positions and the experimentally observed exceptions in Schottky barrier height for some metal/semiconductor interfaces. The electrical properties of lattice mismatched GaInAs/GaAs heterojunctions suggest that Fermi level pinning occurs at misfit dislocations.

The pinning action on the barrier height of a Ga interfacial layer in an Sb/Ga/GaAs structure prepared by molecular beam epitaxy has been tracked as a function of Ga layer thicknesses for both n and p-GaAs (100). The barrier height ÆBn for n-type GaAs (ND=3×1015cm−3), determined by thermal activation measurements and capacitance measurements, changes from 0.8 to 1.0 eV as the Ga layer is increased from zero to three monolayers. The barrier height ÆBp for p-type GaAs decreases in a converse fashion so that the sum ÆBn + ÆBp is equal to the GaAs energy gap. Up to a Ga layer thickness of about one monolayer the barrier height changes are about linearly proportional to thickness.

The action seen is compatible with barrier height changes that are seen when Sb/GaAs junctions are prepared with the original surface alternatively As or Ga rich and subjected to thermal annealing at temperatures up to 250°C.

Al was deposited on Si(l l l) and observed by cross-sectional electron microscopy, both in the annealed and as deposited states. It is shown that Al is strongly textured when deposited on Si(111), with Al(111)//Si(111) and AI<110>//Si<110> or AI(100)//Si(111) and AI<I10>//Si<110>. Annealed samples are completely epitaxial with A1(111)//Si(111) and A1<110>//Si<110>. Lattices imaging of the interfaces shows an amorphous layer (native Si oxide) between Al and Si, in the as-deposited case. The two lattices are in contact only at pinholes in the native oxide and fringes on both sides of the interface are seen to be continuous through the interface only at those points. Annealed samples do not show any amorphous or disordered layer at the interface: The two lattices are completely in contact, with lattice fringes extending from one side of the interface to the other. An atomic model of the annealed interface, based on energy considerations and consistent with TEM observations, is proposed.

Epitaxial Al films have been deposited onto the clean surface of single-crystal Si by ionized cluster beam (ICB) at room temperature. Thermal stability of the film has been examined by SEM, AES depth profiling, ion backscat. tering/channeling, and electrical characterization of the Al-Si interface. It was found that the ICB Al film on Si substrate was remarkably stable up to 550°C although pure Al was used. Alloy penetration at the interface, shift of barrier height, degradation of crystalline quality and development of annealing hillocks on the surface were not observed after the heat treatment. Extremely long electromigration life time was also confirmed. Epitaxial growth on GaAs(100) substrate was attempted and preliminary results are given.

Palladium has been deposited on {1001 and t1111 oriented silicon wafers and also on polysilicon. Cross-sectional specimens for transmission electron microscopy were prepared and heated in-situ. The interfaces between silicide and silicon were rough and the volume changes accompanying heating and compound formation caused elastic strains in the substrates and in one case hillock formation in the products.

We report two phenomena observed in the electrical transport through metal contacts to In0.53Ga0.47 As thin films. First, a surface accumulation layer of electrons is found at the oxide-In0.53Ga0.47 As interface of Pb-oxide-In0.53Ga0.47 As tunnel junctions, suggesting that the surface Fermi level is not pinned in In0.53Ga0.47 As, and ideal ohmic contacts to n- In0 53Ga0.47 As can be made by using low work function metals. Second, we observed a strong oscillatory conductance on the I-V characteristic of electrical transport through In- In0.53 Ga0.47As contacts, with a period approximating the LO-phonon energy of In0.53Ga0.47As. We explain the data by successive phonon emission in the high field transport of ballistic electrons and point out that the experiment is a solid state analogue of the Franck-Hertz experiment.

We summarize photoemission studies using Synchrotron Radiation of the formation of the HgCdTe-Cr interface at room temperature on in situcleaved single crystal substrates. Evidence is found of a Cr-Hg exchange reaction in the subsurface region. The surface and near surface layers appear completely depleted of mercury.

We studied the structural and electrical transport properties of incommensurate PbTe-Bi superlattice films. The properties of those samples were noticeably different from those of commensurate samples. For the incommensurate samples, the satellite peaks, in the 9–29 x-ray scans along the [111] growth orientation, became broader and the ratio of satellite intensities to the Bragg intensity became smaller. The resistances of incommensurate samples were about three times larger than those of corresponding commensurate ones. These features are interpreted by an enhancement of the lateral nonuniformity of interfaces in incommensurate samples. The exponential dependence of the resistance on temperature in incommensurate samples was also in contrast to the logarithmic behavior observed in commensurate ones.

Even though GaAs (110) is the only semiconductor whose surface structure is known with confidence, little is known about its microscopic growth mechanisms. We have used RHEED to study the role of steps in the MBE growth of GaAs on vicinal GaAs(11O) surfaces which were misoriented by less than 2 mrad. After thermally desorbing the initial oxide, 20 layers of GaAs deposited at 700K produced a surface with single atomic-layer steps having an average terrace length of a few hundred Angstroms. Upon annealing to 8OOK, a slow mass migration occurred producing a surface with one thousand Angstrom average terrace lengths and predominantly double layer step heights. The RHEED pattern was nearly instrument limited at in-phase angles of incidence, with little background intensity and bright Kikuchi lines. Subsequent deposition showed only weak oscillations in the RHEED intensity, in contrast to growth on the (001) surface. The period of the observed oscillations indicates that the layer-by-layer growth involves single-layer steps. Growth of as little as 5 atomic layers on a surface with double steps could not be annealed to give a RHEED intensity as great as the first annealed surface. These measurements reconcile previous LEED results with the oxygen adsorption measurements of Ranke. The results clearly show the dominance of steps in the formation of RHEED streaks.

X-rays at grazing incidence have a short, controllable penetration depth and are well suited as a probe of surface and interface structures. This paper examines the possibility applying grazing-incidence reflectivity and Extended X-Ray Absorption Fine Structure (EXAFS) measurements to such systems. Results are presented for an Al-Cu couple for which both high resolution reflectivity and interface EXAFS measurements are made. The latter results are the first interface specific EXAFS data to be reported. Distinct changes in both signals are observed upon annealing, demonstrating the potential of the techniques.

Enhanced core-level peak intensities at angles corresponding to the internuclear axes among the near surface atoms is a characteristic feature of angle resolved XPS. This phenomenon, which is due to constructive interference in forward scattering of photoelectrons, acts, in effect, as a search-light allowing relatively easy mapping out of the structural arrangement atoms in the near-surface region. Examples which illustrate the usefulness of the XPS searchlight effect are presented.

CdTe films have been grown on GaAs substrates with two types of interfaces - one with the epitaxial relation (111)CdTe║ (100)GaAs and the other with (100)CdTe║ (100)GaAs,. High resolution electron microscope observation of the two types of interfaces was carried out in order to determine the role of the substrate surface microstructure in determining the epitaxy. The interface of the former type shows a direct contact between the CdTe and GaAs crystals, while the interface of the latter type has a very thin oxide layer (∼10 Å in thickness) between the two crystals. These observations suggest that details of the substrate preheating cycle prior to film growth is the principle factor in determining which epitaxial relation occurs in this system. The relation between interfacial structures and the origin of the two epitaxial relations is discussed.

In situ Reflection High Energy Electron Diffraction and ex-situ Transmission Electron Diffraction and Ion Channeling have been applied to a reacted Pd-GaAs interface and the results obtained are critically compared. The investigation has been done on the stabilized c(2×8) surface obtained by MBE on GaAs(100) substrates. Smooth surface epitaxial growth has been observed by RHEED as soon as a few monolayers of Pd are deposited at a substrate temperature of about 325°C. TEM diffraction studies indicate the presence of an intermetallic hexagonal structure similar to the orthorhombic Pd5Ga2 but with slightly different lattice parameters due to the possible incorporation of As. A less abundant phase was also identified as an hexagonal structure similar to Pd8As2. Ion Channeling indicates pronounced reduction in scattering yield when the [100] axis of the substrate was aligned with the impinging beam, thus supporting the RHEED analysis. The three techniques listed above were found to be useful for the determination of the epitaxial relationship between the identified phases and the substrate.

Using high resolution lattice imaging techniques, the morphology of thepolycrystalline silicon - single crystal silicon interface has been correlated to (1) the surface treatment used prior to polysilicon deposition, (2) the polysilicon implant dose, and (3) high temperature annealing. Specimens which were chemically oxidized prior to deposition exhibited a continuous layer of amorphous oxide ≈1.5nm thick. High temperature annealing produces small discontinuities in this oxide which allow the polysilicon to make direct contact with, and become epitaxially aligned to, the substrate. Specimens which were etched in HF prior to deposition were characterized by nearly oxide-free interfaces, which, following implantation and annealing, exhibited regions of epitaxial realignment significantly larger than those found in the chemically oxidized films. Heavily implanted films annealed at high temperature displayed almost complete epitaxial realignment.

Thin gold films over GaAs wafers with different dopants (Cr, Si, Te, and Zn) were used to study the role of he substrate electronic properties in the electrical contact and adhesion modification induced by MeV/nucleon heavy ion bombardment. The enhanced adhesion was studied using a scratch test; the results show very different modifications of adhesion depending on the bulk electronic properties of the substrate. The sample with a Cr compensation doped substrate showed enhancement in adhesion for beam doses as low as 1012 ions/cm2, but Si and Te doped (n–type) substrates showed a sudden enhancement in adhesion for doses around 1014 ions/cm2. Samples with Si and Te doped substrates were used to sudy the bombarding ion dE/dx dependence of the induced adhesion for 19F and 35C1 ions with electronic stopping power ranging from 161 eV/Å to 506 eV/Å. In this range the dose threshold fgfjhe ops! of induced adhesion has a power law dependence, D = D0(dE/dx)− (1.90 ± 1.0)

Ion beam mixing is used to produce more uniform Au.Au-Ge and Au-Ge-Ni reacted contacts to GaAs.