Using high-temperature annealing of thin gold nanofilms deposited onto the (001) surface of doped p-GaAs crystal with an ultrathin oxide layer, the nanoclusters of gold (Au2Ga alloy) are fabricated. The gold clusters have the wedge shapes with rectangular bases elongated in [110] direction at GaAs(001) surface. This assertion is confirmed by the data of diagnostics of Au/p-GaAs(001) structures. Anisotropic plasmons localized on equally oriented wedge-shaped Au (Au2Ga) clusters are investigated with the optical reflectance anisotropy spectroscopy and spectroscopy of polarized light reflection. It is shown that the spectral peak at the energy about 0.9 eV in the near infrared range is associated with plasmons polarized along the longest sides of clusters in crystallographic direction [110]. Another peak—at the energy of 1.8 eV—is due to plasmons having polarization in direction [11̅0] .

Wedge-shaped nanoclusters of gold (Au2Ga) are fabricated by high-temperature annealing of a gold nanofilm deposited onto (001) surface of p-doped GaAs crystal with a very thin overlayer of natural oxide. The data of diagnostics confirm the presence in prepared Au/p-GaAs(001) structures of the wedge-shaped Au-intermetallic nanoclusters elongated in [110] direction at GaAs surface. A crystallographic model of the wedge-shaped Au (Au2Ga) nanoclusters conditioned by GaAs(001) surface is discussed in relation with their physicochemical nature. Anisotropic plasmons localized on equally oriented Au-based nanoclusters are detected optically with the reflectance anisotropy spectroscopy and investigated thoroughly with the spectroscopy of polarized light reflection. It is proved experimentally and theoretically that the inhomogeneously broadened infrared spectral peak at the energy about 1.1 eV is associated with plasmons polarized along the wedge-shaped clusters in [110] crystal direction. Another peak - at the energy approximately of 1.8 eV - is due to plasmons having orthogonal polarization in direction [110].

This work demonstrates how to create the structures Au/GaAs with perfect on-surface gold nanoclusters. In doing so, used is covering the GaAs substrate with chemically stable atomic monolayers of sulphur to prevent subsequently a chemical reaction of Au with GaAs. The structures Au/S/GaAs with monolayers of chemisorbed sulphur atoms are fabricated, characterized and studied by polarized reflection spectroscopy. The anisotropy of on-surface gold nanoclusters is established, and the anisotropic plasmons localized in Au clusters are investigated using the spectra of polarized reflection and interpreted theoretically.

The principal role of chemical passivation of GaAs surface in the formation on it of oriented anisotropic nanoclusters of gold is discussed. The nanoclusters are fabricated by thermal annealing of a gold film deposited onto GaAs(001) surface passivated as a preliminary by a monolayer of nitrogen or sulfur atoms. These atoms, bonded chemically to gallium atoms of the crystal surface, form a crystal lattice and prevent the chemical interaction of Au with GaAs. As a result of annealing, the arrays of anisotropic (elongated) nanoclusters of chemically pure Au oriented preferably in crystal [11̅0] direction are formed on passivated GaAs(001) surface. The presence of strong anisotropy and orientation of Au clusters on passivated GaAs surfaces is established by the methods of probe diagnostics and of optical reflectance anisotropy spectroscopy and polarized reflection spectroscopy. Using an optical model of plasmonic polarizability of elongated Au spheroids, it is shown that the spectral features observed in polarized reflection originate from anisotropic plasmons of Au nanoclusters polarized mainly in direction [11̅0] of crystal.

•Electric field on sulfur-passivated n- and p-GaP(001) surfaces is probed by RAS and SXPS;•Sulfur passivation of n-GaP(001) surface causes decrease in the surface electric field;•Passivation of p-GaP(001) surface increases surface electric field dramatically;•Surface electric field change is related to the modification of the surface dipole;•The dipoles modify band potentials only in the immediate vicinity of the surface.

The surface electric field in GaP(0 0 1) passivated with aqueous and alcoholic sulfide solutions is studied by reflectance anisotropy spectroscopy using data on the surface chemical and electronic structure obtained by synchrotron-radiation X-ray photoelectron spectroscopy. Treatment of n-GaP(0 0 1) surface with a sulfide solution decreases the surface electric field depending on sulfide solution composition. In particular, passivation with the solution of ammonium sulfide in 2-propyl alcohol turns the total surface electric field almost to zero, while passivation with the aqueous ammonium sulfide solution reduces the surface electric field in a lesser extent. On the other hand, sulfide treatment of p-GaP(0 0 1) surface enhances the surface electric field dramatically and this enhancement is nearly independent of the sulfide solution composition. Such changes in the surface electric field can be related to the modification of the dipole associated with chemical bonds in the passivating layer.

The principal role of chemical passivation of GaAs surface in the formation on it of oriented anisotropic nanoclusters of gold is discussed. The nanoclusters are fabricated by thermal annealing of a gold film deposited onto GaAs(001) surface passivated as a preliminary by a monolayer of nitrogen or sulfur atoms. These atoms, bonded chemically to gallium atoms of the crystal surface, form a crystal lattice and prevent the chemical interaction of Au with GaAs. As a result of annealing, the arrays of anisotropic (elongated) nanoclusters of chemically pure Au oriented preferably in crystal [110] direction are formed on passivated GaAs(001) surface. The presence of strong anisotropy and orientation of Au clusters on passivated GaAs surfaces is established by the methods of probe diagnostics and of optical reflectance anisotropy spectroscopy and polarized reflection spectroscopy. Using an optical model of plasmonic polarizability of elongated Au spheroids, it is shown that the spectral features observed in polarized reflection originate from anisotropic plasmons of Au nanoclusters polarized mainly in direction [110] of crystal. Keywords: semiconductor surface, nitride passivation, gold nanoclusters, anisotropic plasmons, polarized reflectance.

Herein, the formation of Au nanoclusters on nitridized GaAs(001) surface is described, as well as the structure diagnostics and spectroscopic studies which reveal a strong anisotropy of the plasmons localized on the clusters. Principal aspects of the work are the following. Technologically, structures of Au/N/GaAs are fabricated with a monolayer of nitrogen atoms chemisorbed preliminary onto GaAs substrate to prevent its reaction with subsequently deposited Au film. Annealing of the structures Au/N/GaAs results in the appearance of anisotropic nanoclusters of chemically clean gold on GaAs surface. Experimentally, the existence of in‐surface anisotropy of Au clusters is verified with the atomic force microscopy and it is investigated with the resonant optical spectroscopies of anisotropy reflectance and polarized reflection. All the methods are applied jointly for the detailed study of anisotropic plasmons revealed in gold nanocluster arrays. Theoretically, the plasmon‐conditioned features observed in optical polarized spectra are interpreted using an optical model of in‐surface anisotropic plasmons in Au nanospheroids. As a result, the macroscopic anisotropy and orientation of gold nanoclusters and their plasmons relative to the crystallographic axes of GaAs substrate are unambiguously established and reliably specified.

A principal role of chemical passivation of GaAs surface in the formation of oriented anisotropic on-surface nanoclusters of gold is discussed. The gold nanoclusters are fabricated by thermal annealing of the gold film deposited onto GaAs(001) surface passivated preliminary by an atomic monolayer of nitrogen or sulphur. These atoms forming a crystal lattice are bonded chemically to gallium atoms of the crystal surface to prevent chemical interaction of Au with GaAs. Annealing Au on passivated GaAs(001) surface results in formation of arrays of anisotropic (elongated) nanolusters of chemically pure Au oriented preferably in crystal direction. The presence of strong anisotropy and orientation of Au clusters on passivated GaAs surfaces is established by the methods of probe diagnostics and the optical techniques of reflectance anisotropy spectroscopy and polarized reflection spectroscopy. Within an optical model of plasmon polarizability of elongated Au spheroids, it is shown that the spectral features observed in polarized reflection originate from anisotropic plasmons polarized in Au nanoclusters predominantly in direction on GaAs(001) surface.

The effect of chemical passivation in solutions of ammonium sulfide (NH4)(2)S on the optical and electronic properties of the surface n-InP (001) is studied. It is shown that treatment in a 4% aqueous solution of (NH4)(2)S leads to a twofold decrease in the surface field and charges localized in this region. Treatment in a 4% alcohol solution (NH4)(2)S leads to a decrease in these parameters by a factor of 3, and, moreover, the barrier photovoltage decreases by a factor of 3.

The effect of chemical passivation in solutions of ammonium sulfide (NH4)2S on the optical and electronic properties of the n-InP (001) surface has been studied. It has been shown that treatment in a 4% aqueous solution of (NH4)2S leads to a decrease of surface band bending and localized charges in near-surface region in the 2 times. Processing in a 4% alcoholic solution of (NH4)2S leads to a decrease in these parameters in 3 times, and moreover, the barrier photovoltage and also reduces in three times.

The Schottky nanostructures Au/GaAs with Au nanoclusters are prepared by annealing of thin gold films deposited on nitridized GaAs(001) surface. The nanostructures are diagnosed nanoscopically and investigated by optical reflection anisotropy spectroscopy. The Au nanoclusters arrays of two types are found to be formed respectively under and over GaAs surface. The energies of local plasmons of the arrays are detected at 1.6 and 2.15 eV, respectively. The latter plasmons possess in-surface anisotropy which causes in optical anisotropy spectra the intensive resonant feature at energy about 2 eV. The plasmon anisotropy is studied comprehensively, and the results are interpreted theoretically.

Efficiency of in situ AlGaAs and GaP and ex situ nitride surface passivation of p+ GaAs nanowires was studied. The efficiency was estimated by comparing of the photoluminescence intensity of the passivated nanowires with the unpassivated nanowire. The AlGaAs and nitride passivation lead to the increasing of the PL intensity by three orders of magnitude while the GaP passivation increases PL intensity only by one order. Photodegradation of the passivated NWs under intensive laser illumination was observed. AlGaAs, GaP and nitride passivated NWs photodegrade after one-minute exposure under laser power densities of 500, 300 and 30 kW/cm2, respectively.

A procedure is developed for controlled creation of Au nanoclusters by annealing of a gold film deposited onto GaAs(0 0 1) crystal surface. The nanoclusters of Au are formed at GaAs surfaces covered by either a natural oxide layer or a monolayer of gallium nitride. Surface morphology of the Au/GaAs structures with Au nanoclusters is characterized by scanning probe diagnostics and localized plasmons of the nanoclusters are investigated by optical reflection spectroscopy. In annealing Au film dissimilar gold nanoclusters are found to occur on oxidized or nitridized GaAs(0 0 1) surface via chemical transformation or recrystallization of Au film, respectively. Gold nanoclusters of the two types cause resonant peaks in optical reflectance spectra at the energies of 1.6 eV and 2.15 eV. Using the data of optical spectroscopy and their theoretical analysis we assign the former peak to localized plasmons of prolate Au nanoclusters buried into GaAs crystal near its surface. Another peak at 2.15 eV is attributed to plasmons of oblate Au nanoislands appearing on nitride overlayer which prevents any chemical contact of Au with GaAs bulk. The asserted existence of Au nanoclusters in the bulk of GaAs crystal near its oxidized surface is expected to be helpful in elucidating the nature and structure of Ohmic Au-GaAs contacts.

The structures Au/GaAs(001) with gold nanoclusters are created by annealing of Au films deposited onto GaAs surface. The samples are diagnosed stepwise by scanning probe microscopy. Using reflectance anisotropy spectroscopy, Au clusters are established to possess plasmons with the in-surface anisotropy. The measured anisotropy spectrum consists of a resonant feature near the energy of 2 eV typical of local plasmons of Au clusters. The results are explained theoretically, and the new spectral feature is assigned to anisotropic plasmons of Au nanoclusters located on GaAs surface.

In semiconductors under tightly-focused photocarrier excitation, the lateral variation of carrier concentration induces a lateral variation of photovoltage. In chemically-passivated p-type GaAs films at 300 K, we show experimentally and theoretically that the photovoltage lateral dependence is able to block the photoelectron diffusion, thus reducing the effective charge diffusion constant by a factor of ≈5 with respect to surface-free conditions and producing a self-trapping of photoelectrons. This effect is not present for surface-free and for oxidized samples, for which the photovoltage magnitude is strongly reduced. The photovoltage lateral variation also induces a coupling between charge and spin diffusion. Because of this coupling, the effective spin diffusion constant is significantly larger than the effective charge one.

Gold nanoclusters of two different kinds are found to occur on annealing of thin Au films deposited on either oxidized or nitridized GaAs(001) surfaces. The morphology of Au/GaAs interfaces is characterized, and the gold nanoclusters are established to cause two resonant peaks in optical reflectance spectra at the energies of 1.6 eV and 2.15 eV. Using the data of reflection spectroscopy and theoretical analysis, we assign the latter peak to localized plasmons of Au nanoislands located on Au/GaAs surface. The former peak is attributed to plasmons of prolate Au nanoclusters buried in GaAs crystal just near its surface. As well, plasmonic anisotropy of Au nanoclusters formed on nitridized GaAs surfaces is detected using reflectance anisotropy spectroscopy.

The electronic properties of semiconductor AIIIBV nanowires (NWs) due to their high surface/volume ratio can be effectively controlled by NW strain and surface electronic states. We study the effect of applied tension on the conductivity of wurtzite InxGa1-xAs (x ∼ 0.8) NWs. Experimentally, conductive atomic force microscopy is used to measure the I-V curves of vertically standing NWs covered by native oxide. To apply tension, the microscope probe touching the NW side is shifted laterally to produce a tensile strain in the NW. The NW strain significantly increases the forward current in the measured I-V curves. When the strain reaches 4%, the I-V curve becomes almost linear, and the forward current increases by 3 orders of magnitude. In the latter case, the tensile strain is supposed to shift the conduction band minima below the Fermi level, whose position, in turn, is fixed by surface states. Consequently, the surface conductivity channel appears. The observed effects confirm that the excess surface arsenic is responsible for the Fermi level pinning at oxidized surfaces of III-As NWs.

Modification of the surface chemical composition and electronic structure of the native-oxide-covered p-GaP(001) surface by treatment with sulfide solution is studied by high-resolution synchrotron photoemission spectroscopy (SXPS) and reflectance anisotropy spectroscopy (RAS). Treatment of the p-GaP(001) surface with a solution of ammonium sulfide in 2-propanol causes removal of the native oxide layer and formation of a passivating layer consisting mainly of gallium sulfides and sulfates. The latter species are formed due to oxidation of sulfides with hydroxyl groups existing in the solution. After such a treatment the downward surface band bending of about 0.5 eV remains essentially unaffected, while the electronic work function increases by 0.6 eV indicating modification of the surface dipole. As a result, the valence band maximum at the surface shifts to 5.6 eV. In reflectance anisotropy spectra the surface dipole modification produces an essential increase of the anisotropy signal in the spectral region of the direct optical transition point E-1 indicating considerable increase of the near-surface electric field. This dipole-induced near-surface electric field remains essentially unchanged on air exposure of the sulfur-treated p-GaP(001) surface for at least 6 months.

Fermi level pinning at the oxidized (110) surfaces of III-As nanowires (GaAs, InAs, InGaAs, AlGaAs) is studied. Using scanning gradient Kelvin probe microscopy, we show that the Fermi level at oxidized cleavage surfaces of ternary AlxGa1−xAs (0 ≤ x ≤ 0.45) and GaxIn1−xAs (0 ≤ x ≤ 1) alloys is pinned at the same position of 4.8 ± 0.1 eV with regard to the vacuum level. The finding implies a unified mechanism of the Fermi level pinning for such surfaces. Further investigation, performed by Raman scattering and photoluminescence spectroscopy, shows that photooxidation of the AlxGa1−xAs and GaxIn1−xAs nanowires leads to the accumulation of an excess of arsenic on their crystal surfaces which is accompanied by a strong decrease of the band-edge photoluminescence intensity. We conclude that the surface excess arsenic in crystalline or amorphous forms is responsible for the Fermi level pinning at oxidized (110) surfaces of III-As nanowires.