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We have investigated the growth of thin indium layers on As- and Ga-terminated GaAs(001) surfaces by reflectance anisotropy spectroscopy (RAS), low energy electron diffraction (LEED), and auger electron spectroscopy. Room temperature deposition of indium on the $(2\ifmmode\times\else\texttimes\fi{}4)/c(2\ifmmode\times\else\texttimes\fi{}8)$ surface and subsequent annealing at 450 \ifmmode^\circ\else\textdegree\fi{}C leads to the formation of an In-terminated surface showing a $(4\ifmmode\times\else\texttimes\fi{}2)$ LEED pattern, accompanied with strong changes in the measured surface optical anisotropy. When indium is deposited onto the $(4\ifmmode\times\else\texttimes\fi{}2)/c(8\ifmmode\times\else\texttimes\fi{}2)$ surface, on the contrary, the $(4\ifmmode\times\else\texttimes\fi{}2)$ In-terminated surface is already formed at room temperature deposition without needing annealing, as demonstrated by the RAS spectra. The finding that almost identical RAS spectra and $(4\ifmmode\times\else\texttimes\fi{}2)$ LEED patterns are obtained in both cases shows that the same final atomic structure is achieved. Finally, we conclude that the structure of the In-terminated surface is similar to that of the clean Ga-rich surface, although a more detailed model would need accurate calculations of the microscopic origin of the measured anisotropy.

Berlin, host of this year's European Workshop on Metal-Organic Vapour Phase Epitaxy (EW MOVPE VII), is a city which has developed into one of the ‘centres of excellence’ in the field of MOVPE. An overview of MOVPE activities and related issues in the German capital — from basic growth studies to research and development of devices — is presented here.

In this study we report on the microscopic structure of GaSb(001) c(2\ifmmode\times\else\texttimes\fi{}6) surfaces prepared by Sb decapping. Molecular beam epitaxy grown GaSb(001) layers capped with a protective Sb layer were transferred through the atmosphere into an UHV-analysis system and investigated by scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). After thermal desorption of the capping layer clear c(2\ifmmode\times\else\texttimes\fi{}6) LEED patterns were observed. STM images show flat surface areas with a rowlike, somewhat disordered structure. High-resolution images resolve individual Sb dimers on the surface. The surface is covered by an incomplete layer of dimerized Sb, adsorbed on a complete second layer of Sb, which is also dimerized in that regions not covered by the fractional Sb top layer.

The influence of antimony as surfactant on the growth mode of indium on GaAs(001) has been investigated for deposition at various temperatures. Clean surfaces of (2 × 4) reconstruction were prepared in UHV by thermal desorption of a protective arsenic cap deposited on top of homoepitaxially grown MBE layers. Before In deposition, 2 ML Sb were pre-deposited on top of the clean GaAs surface of part of the samples. The In growth mode was then monitored by AES and compared with that occurring during In growth on GaAs without an Sb interlayer. After removal of the samples from UHV, SEM investigations show regularly shaped, flat In islands oriented along the 〈110〉 substrate directions. In comparison, In islands grown without an Sb interlayer also show a preferential orientation along the 〈110〉 substrate directions, but differ in shape and size. Low-temperature In deposition (120 K) leads to the formation of a continuous In layer, which tears during warm up to room temperature. An exchange between surfactant material and indium during growth is found for both low- and room-temperature In deposition. X-ray diffraction measurements show a strong influence of the Sb surfactant on the crystallinity of the In film.

The growth of thin indium-layers on the GaAs(100) As-rich (2 × 4) c (2 × 8) surface has been investigated by reflectance anisotropy spectroscopy (RAS), LEED and AES. Clean surfaces of the (2 × 4) c (2 × 8) reconstruction were prepared in UHV by thermal desorption of a protective arsenic layer deposited on homoepitaxially grown MBE layers. Room temperature deposition of indium on the (2 × 4) c (2 × 8) surface and subsequent annealing at 450°C leads to a 90° rotation of symmetry in the LEED pattern at a threshold coverage of 0.5 monolayers, i.e. a change from the (2 × 4) c (2 × 8) to the (4 × 2) c (8 × 2) reconstruction. The RAS spectra show the evolution of a distinct negative feature at 1.8 eV, that shifts to 2.1 eV after annealing, corresponding to optical transitions attributed to In-dimers orientated along the [011]-direction. AES analysis shows a change in growth mode beyond 0.5 ML indicating saturation of all available adsorption sites at this coverage and RAS spectra show a contribution from additional disordered In. The AES spectra display no evidence of a surface exchange reaction between gallium and arsenic atoms, thus indicating a surface termination by In-dimers adsorbed on a layer of As.

A new process for chemical passivation of III–V semiconductor surfaces in metalorganic vapour phase epitaxy (MOVPE) is developed. A passivation layer is deposited directly after growth in the reactor. It consists of amorphous arsenic or a double-layer package of amorphous phosphorus and arsenic, which are grown by photo-decomposition of the group-V hydrides. These layers (caps) serve to protect the surfaces against contamination in air after removing the samples from the MOVPE growth reactor. Such passivation is applicable e.g. for a two-step epitaxy or for further surface characterizations.

The microscopic structure of the Sb stabilized GaAs(100)-(2 3 4) surfaces is investigated combining reflectance anisotropy spectroscopy with first-principles total energy minimization and tight-binding calculations of optical properties. We show that the model accepted so far, containing three Sb dimers in the outermost layer, is not a stable surface geometry. Our results reveal a coexistence of Sb and Ga dimers on the Sb-stabilized s2 3 4d surface. [S0031-9007(96)01679-1]

Scanning tunneling microscopy (STM) was used to study clean GaAs(100) surfaces prepared by thermal desorption of a protective Arsenic layer. The GaAs samples were grown by MBE using an As 2 cracker cell. After transfer through atmosphere and insertion into the UHV chamber, clean, well ordered surfaces with different reconstructions were prepared by thermal annealing. The atomic structure and the morphology of the surfaces were found to depend sensitively on the annealing procedure. For several differently reconstructed surfaces STM images with atomic resolution were obtained similar to those recently published for in-situ-MBE investigated surfaces. These results demonstrate that the As-decapping technique is, in fact, a versatile tool for preparing well-defined GaAs(100) surfaces.

The electrical resistivity of thin crystalline antimony films (thickness 8 and 27 nm) is investigated in the temperature range 1.6–300 K with magnetic fields up to 8 Tesla applied parallel to the film plane. The films were prepared by evaporation on cleaved (110) surfaces of GaAs substrates. Classical magnetoresistance is observed over the whole temperature range. Below approximately 6 K the resistivity exhibits a In ( T ) increase which can be analyzed in terms of electron localization and electron-electron interaction theory. Accounting for the classical magnetoresistance the magnetic-field dependence of the resistance can be described with an appropriate theory leading to the characteristic length scales L ϑ and L so .

Ordered Sb monolayers and multilayers on GaAs(110) and InP(110) have been studied in in situ by measuring the optical anisotropy (reflectance anisotropy spectroscopy) and the difference of the reflectivity with respect to the clean surface for linear polarized light (surface differential reflectance). The preparation was performed by annealing a 4–5 multilayer thick Sb film on ultrahigh vacuum-cleaved InP(110) and GaAs (110) substrates, which induces an ordered multilayer film of a metastable crystal structure termed 'substrate-stabilized structure'. Annealing to higher temperatures can be utilized to prepare a highly ordered monolayer film with a pseudomorphic lattice structure. Both monolayers and multilayers have a geometrically anisotropic structure owing to the formation of Sb chains, which are derived either from the pseudomorphic growth or from the double-layer structure of the Sb crystal lattice, respectively. The substrate-stabilized multilayers show a strong optical anisotropy of approx...

The growth of thin Sb layers on GaAs(100) was studied in ultra high vacuum by means of Raman scattering and spectroscopic ellipsometry. Clean (100) surfaces were prepared by heating As-passivated MBE-grown GaAs substrates. The Raman spectra taken after stepwise Sb deposition show that the overlayer grows in an amorphous structure up to coverages between 20 and 30 monolayers (ML). For larger coverages the E g and A 1g phonon modes of crystalline Sb are detected indicating the crystallisation of the overlayer. After the crystallisation, the LO phonon mode of the GaAs substrate is substantially broadened. The structural transition of the Sb is also reflected in changes in the imaginary part of the dielectric function ϵ(ω) obtained by ellipsometry. Both the LO broadening and the changes in ϵ(ω) can be interpreted by a transition to a metallic Sb overlayer. Crystalline overlayers below 20 ML thickness showing a metallic like dielectric function can be obtained by annealing amorphous Sb overlayers to approximately 180°C.

MBE-grown samples capped with a protective Sb layer were used to study clean (100) surfaces in UHV. By thermal desorption of the Sb cap layer GaSb surfaces exhibiting c(2 X 6) reconstruction were prepared, then studied by reflectance anisotropy spectroscopy, low energy electron diffraction and Auger electron spectroscopy. The results of this experimental analysis allowed us to determine for the first time the surface related optical anisotropy of the c(2 X 6) reconstruction of GaSb(100) in the range 1.5-5.5 eV, Reflectance anisotropy spectroscopy features related to optical transitions of surface Sb dimers are identified and discussed. Moreover, the appearance of an optical anisotropy related to the linear electro-optic effect at the E(1) bulk critical point shows the existence of band bending at GaSb decapped surfaces.

This year's International Conference on Metal-Organic Vapour Phase Epitaxy (ICMOVPE) will be held in Berlin from 3rd to 7th of June. Specialists from all over the world will present the latest advances in science, technology, and applications of MOVPE and related growth techniques. The eleventh meeting of this well-known conference series will take place in the Ludwig-Erhard-Haus, that was designed by the famous British architect Nicholas Grimshaw. Besides serving as a conference centre the building houses the Berlin Chamber of Commerce. It may thus be the appropriate place to symbolise that MOVPE has become a success story not only from the scientific point of view but also from the economic one.

The growth of indium‐layers in the monolayer regime on As‐rich (2×4)/c(2×8)‐ and Ga‐rich (4×2)/c(8×2)‐GaAs(100) surfaces has been investigated by scanning tunneling microscopy (STM), low‐energy electron diffraction (LEED), Auger electron spectroscopy (AES) and reflectance anisotropy spectroscopy (RAS). Clean (2×4)‐ and (4×2)‐reconstructed surfaces were prepared in UHV by thermal desorption of a protective arsenic layer deposited on top of GaAs(100) surfaces grown in a molecular beam epitaxy (MBE)‐system. For the (2×4) reconstruction, the STM images show As‐dimer rows consisting mostly of two dimers per unit cell in the outermost layer. Besides a large number of kinks in the dimer rows, a surface roughness corresponding to about three bilayer steps (8.4 A) is observed due to multiple layer nucleation during MBE growth. After deposition of indium and subsequent annealing to approximately 450 °C a well ordered reconstruction with c(8×2)‐symmetry is established. The STM images show a pattern consisting of kin...