Compound Semiconductor Surfaces Research Articles

Surface-energy-induced mass-transport phenomenon in annealing of etched compound semiconductor structures: Theoretical modeling and experimental confirmation

A comprehensive model of the mass-transport phenomenon at the surface of compound semiconductors has been developed and experimentally confirmed. In the model, the effect of surface curvature on thermal decomposition and the resulting diffusion and regrowth has been formulated, and a differential equation has been derived that describes the temporal evolution of any (spatially) slowly varying surface profile during mass transport. The model predicts an exponential decay of sinusoidal profiles with a fourth power of spatial wavelength dependence, and a grading of single mesa steps with a fourth root of time dependence. Good agreement with the model has been obtained in a systematic experimental study employing etched structures in InP. This study yields the low value of 1.5 eV for the activation energy of the mass-transport process in InP.

A computer simulation of the recombination process at compound semiconductor surfaces and hetero-interfaces

The complex recombination process through quantum states at compound semiconductor surfaces and hetero-interfaces is analyzed in a unified manner on the computer, using the unified disorder induced gap state (DIGS) model. Recombination through uniformly distributed states at surfaces and hetero-interfaces, and that through U-shaped surface states at GaAs surfaces subjected to various surface treatments, are specifically analyzed. The result indicates that the effective surface recombination velocity is not constant, but is strongly dependent on the excitation intensity and the location of charge neutrality level, EHO. PL intensity enhancement after photochemical oxidation in water and sulfur treatments (Na2S, (NH4)2S) is shown to be not due to reduction of the durface states, but due to the generation of a fixed charge, whereas photochemical HCl treatment reduces the surface states significantly.

Polarity determination in (001)-oriented AIII– Bvcompound semiconductors by the Kossel technique and chemical etching

Kossel line profiles have been analyzed in order to determine the polarity of III – V compound semiconductor surfaces without other means. In view of the importance of differentiating [110] and [1[unk]0] zones on (001) surfaces especially of optoelectronic materials GaAs, GaP, and InP the results of Kossel experiments have been correlated to etch experiments. The long axes of pits produced by common etchants on the (001) surface align always parallel to the [1[unk]0] direction.

The electronic properties and control of semiconductor interfaces

Much progress has been made towards the understanding and elimination of the Fermi level pinning problem at compound semiconductor surfaces and interfaces. This progress includes the discovery of several new techniques for reducing and controlling the surface state density and the achievement of metal work function dominated barrier heights at metal/(100) GaAs interfaces. This paper will review this work and the relevance of various Fermi level pinning theories to these results.

Hydrogen adsorption on compound semiconductor surfaces

We present the results of the total-energy calculations for different adsorption geometries of atomic hydrogen on GaAs (110) and the corresponding changes in the surface electronic states. In particular we discuss the problem of the quenching of the substrate relaxation.

In Situ Observations of Beam-Induced Effects During High-Resolution Electron Microscopy

AbstractA variety of electron-beam-induced effects, including oxidation, reduction and surface rearrangements are observed to occur at surfaces of oxides, fluorides and compound semiconductors during electron irradiation within the electron microscope. The extent and type of surface modifications observed are shown to depend upon the irradiation level, the residual microscope vacuum and the specimen temperature. For example, ex situ annealing of compound semiconductors leads to different end-products compared with in situ irradiation, thus showing that residual gas components can have a strong influence on the surface reactions. Electron irradiation of rutile during annealing at high temperature under ultrahigh vacuum conditions caused the rapid development of well-facetted holes without the usual intermediary phase seen at room temperature in conventional vacuum.

Surface rotational phonons on the cleavage faces of tetrahedrally coordinated compound semiconductors

Surface rotational phonons associated with atomic displacements about the relaxed minimum-energy surface geometry are shown to be responsible for a new branch in the surface excitation spectra of GaAs(110) observed via inelastic helium atom scattering. These phonons are associated with the rehybridization-induced surface reconstructions on the cleavage surfaces of both zincblende and wurtzite structure compound semiconductors. For zincblende structure materials, the frequencies of these phonons are predicted for the (110) surfaces of GaP, GaAs, GaSb, InP, InAs, InSb, ZnS, ZnSe, and CdTe. For wurtzite structure materials, the frequencies are predicted for the (101̄0) surfaces of ZnO, ZnS, ZnSe, CdS, and CdSe. A discussion is given on the role of tetrahedral symmetry in determining the nature and consequences of these phonons.

XPS intensity analysis for assessment of thickness and composition of thin overlayer films: Application to chemically etched GaAs(100) surfaces

AbstractQuantification by XPS intensity analysis of thin multicomponent overlayers, like the native oxides forming on compound semiconductor surfaces, is discussed in some detail. In particular, the advantage of exploiting the attenuated emission from substrate core levels with different probing depths is emphasized, in order to obtain a precise measure for the overlayer thickness dimension. For GaAs(100) treated with different chemical etches, estimates are obtained for the thickness of the native surface oxide formed after exposure to air, of 6–8 Å. The elemental composition of the surface oxide is close to the stoichiometric metal: oxygen ratio of the bulk oxides Ga2O3 and As2O3, in perfect agreement with the measured core‐level shifts (1.4 ± 0.2 and 3.0 ± 0.1 eV for the Ga and As 2p levels, respectively). On a CF4 plasma‐etched sample, a surface reaction layer of gallium fluoride was found with a composition close to GaF2 and an estimated thickness of ∼23 Å. This paper also discusses how to determine the kinetic energy dependence of the electron escape depth, expressed in terms of an exponent m (γ Em), by working out consistent estimates for the surface oxide (fluoride) thickness via two different approaches. Values for m are obtained in the range 0.5–0.6, in excellent agreement with previously reported data on electron escape depth for semiconductors.

Effect of exposure to group III alkyls on compound semiconductor surfaces observed by x-ray photoelectron spectroscopy

Clean surfaces of GaAs and InAs prepared by molecular beam epitaxy have been epitaxy have been exposed to trimethylgallium and diethylgalliumchloride at various temperatures and the resultant change has been observed in situ by X-ray photoelectron spectroscopy. Saturation of amount of Ga deposited onto the surface to about 1 monolayer has been observed at substrate temperature above 320°C, which results in atomic layer epitaxy. No appreciable increase of carbon nor chlorine has been observed after exposure to group III alkyls.

Rotational surface phonons on (110) cleavage surfaces of zincblende-structure compound semiconductors

A newly observed branch of surface phonon modes characteristic of the GaAs(110) surface is interpreted in terms of bond-length-conserving rotations of the top layer atoms. This model yields calculated photon frequencies which agree well with the experimental values. The rotational surface phonon modes are predicted to exhibit small dispersion both along and perpendicular to the (110) zigzag chain. The frequencies of these phonons also are predicted for the (110) surfaces of GaP, GaSb, InP, InAs, InSb, ZnS, ZnSe and CdTe.

Tunneling microscopy of 2H-MoS2: A compound semiconductor surface.

Molybdenum disulfide, a layered semiconductor, is an interesting material to study with the tunneling microscope because two structurally and electronically different atomic species may be probed at its surface. We report on a vacuum scanning tunneling microscopy study of 2H-MoS2. Atomic resolution topographs and current images show the symmetry of the surface unit cell and clearly reveal two distinct atomic sites in agreement with the well-known x-ray crystal structure.

Surface kinetic processes and the morphology of equilibrium GaAs(100) surfaces: A Monte Carlo study

The morphological behavior of model static surfaces of compound semiconductors, as well as dynamic growth fronts relaxing towards their equilibrium behavior upon termination of growth, is studied via Monte Carlo simulations based upon the configuration-dependent reactive incorporation model. It is found that anion desorption, cation migration, and surface reconstruction play a crucial role in controlling the surface morphology and their interplay can explain the experimentally observed dependence of morphology on the substrate temperature.

Cleavage-related electronic states of Al–InP(110) interfaces

Cathodoluminescence spectroscopy studies of III–V compound semiconductor surfaces and their metal interfaces show that the optical emission of deep‐level surface and interface states depend on semiconductor‐surface morphology. Spatially resolved measurements reveal metal‐induced interface states at cleavage steps whose optical emission properties depend on electron‐beam injection level. The density and spatial distribution of such metal‐cleavage‐related states may account for variation in electronic measurements reported for clean III–V compound semiconductor/metal interfaces.

Ab initio theory of polar semiconductor surfaces. I. Methodology and the (22) reconstructions of GaAs(111).

A methodology is developed for the theoretical study of the polar surfaces of compound semiconductors. It is based on the calculation of the total energy in the context of density-functional theory in the pseudopotential approximation. The method is used to investigate the (2\ifmmode\times\else\texttimes\fi{}2) reconstructions of GaAs(111). Emphasis is given to the relative chemical potential, which plays a crucial role in determining the lowest-energy geometry for surfaces with different stoichiometries. The total-energy versus chemical-potential curves indicate that there are at least two stable reconstructions. We predict one to be an As-triangle geometry and the other the Ga vacancy.

Atom-selective imaging of the GaAs(110) surface.

We report the first voltage-dependent scanning tunneling microscope images of a compound semiconductor surface, GaAs(110). Images show either only Ga atoms, or only As atoms, depending on the bias voltage. By combining voltage-dependent images with theoretical calculations, we quantitatively determine surface structural parameters which cannot be inferred from the images alone.

Atomic forces from electronic energies via the Hellmann-Feynman theorem, with application to semiconductor (110) surface relaxation.

A method has been devised for computer simulations of covalently bonded systems, such as semiconductors. The method uses noncentral and nonlocal effective potentials generated from the electronic structure via the Hellmann-Feynman theorem. As an elementary example, the method is applied to the time-dependent relaxation of the (110) surfaces of various III-V and II-VI compound semiconductors, starting from an ``ideal'' unrelaxed surface.

Charge transfer from chemical shifts at (110) surfaces of III–V compound semiconductors

Abstract Surface charge-transfer are calculated from surface core-level shifts determined by Eastman et al. and Taniguchi et al. by using soft X-ray photoemission spectroscopy. A simple electrostatic model which was first applied by Shevchik et al. to the analysis of bulk data is adapted for surfaces of compound semiconductors. The charge transferred from cations to anions is found to be the same in the bulk and at the (110) surfaces of GaP, GaAs, GaSb, and InSb.

Atomic geometries of zincblende compound semiconductor surfaces: Similarities in surface rehybridizations

Atomic geometries of zincblende compound semiconductor surfaces are reviewed in the light of recent work done on (111) and (311) GaAs surfaces. The geometries derived from low-energy electron diffraction and from energy-minimization calculations, and electron energy-loss spectroscopy data on the surface electronic transitions indicate that the microscopic structures of the (110), (111)-A and (311)-B surfaces have common features and suggest that similar bond rehybridization mechanisms dominate atomic displacements at these surfaces.

Atomic geometries of zincblende compound semiconductor surfaces: Similarities in surface rehybridizations

Atomic geometries of zincblende compound semiconductor surfaces: Similarities in surface rehybridizations

The schottky-barrier of GaAs(110)-Sb studied by UV photoemission

The band bending changes due to deposition of Sb on cleaved GaAs(110) surfaces are studied by UV photoemission spectroscopy (UPS). The band bending vs coverage curves are evaluated from measurements of the work function change Δ and a determination of the surface dipole contribution within Δ. For both n - and p -type material depletion layers are formed with saturation band bendings of 650 meV and −500 meV, respectively. These values are essentially reached for Sb coverages around 0.1 monolayer. The results fit well to predictions of the defect model for the explanation of Schottky-barriers on III–V compound semiconductor surfaces.