Core-level photoemission spectra of the As 3d, Ga 3d and Bi 5d core levels were recorded for the BiGaAs (111)A-(2×2) surface. From the early stages of Bi growth, there are two distinct chemical environments for Bi. Surface Bi is bonded to both As and Ga atoms. The deposition of approximately 1 ML of Bi removes the dangling bonds from the surface As and Ga atoms, which are associated with the (2×2) vacancy-buckling structure. Annealing to 350°C reverses this process and surface dangling bonds for Ga reappear. When the Bi had fully desorbed at 425°C, photoemission and LEED results showed that the surface recovers the (2×2) vacancy structure but with a larger degree of surface disorder than that found before the deposition of Bi.

We describe a study of samples grown by molecular-beam epitaxy, designed to examine the limitations to silicon (Si) δ-doping of gallium arsenide (GaAs) at elevated growth temperatures. Samples (Si δ-doped to 1 × 10 13 cm −2 ) were grown at 630°C, during which the growth was paused (for times between 0 and 18 min) after depositing the Si. Total electron sheet densities were measured (using Hall and Shubnikov-de Haas (SdH) effect measurements) to determine the electrically active Si concentration. The free electron concentration showed a reduction from about 8 × 10 12 cm −2 for zero pause time, to 5 × 10 12 cm −2 for 18 min pause time. These results can be explained convincingly using simple models of impurity background in the MBE chamber or surface aggregation. Further experiments to distinguish these mechanisms are discussed.

The circular dichroism of angle-resolved photoelectron spectra was investigated for core-levels from clean and hydrogen exposed GaAs (111) surfaces. It was found that the circular dichroism of Ga-3d and As-3d photoelectrons shows clear dependence on the emission angle of the photoelectrons and the sample surface. It is proposed that the experimental results may be interpreted primarily in terms of the interference of photoelectrons affected by the anisotropic field in the surface layer of GaAs (111).

The (111)B surface of GaAs has been investigated using scanning tunnelling microscopy (STM) and a number of different reconstructions have been found at different surface stoichiometries. In accordance with electron diffraction studies, we find the series (2 × 2), (1 × 1)LT, (√19×√19) and (1 × 1)HT with increasing annealing temperature, corresponding to decreasing surface As concentration. We find the (1 × 1)LT to be a mixture of the local structures of the (2 × 2) and (√19×√19) phases as well as some elements of a (3 × 3) structure. This is behaviour consistent with a system, dominated by the supply of As adatoms to the surface, and may be an example of a continuous phase transition. Above the (1 × 1)LT transition, atomic resolution images of the (√19×√19) surface reveal only a threefold symmetry of the hexagonal structural units, brought about by inequivalent surface bonding. This is responsible for the disorder found in the (√19×√19) reconstruction, since the structure may form in one of two domain rotations. At lower surface As concentration, the (1 × 1)HT surface adopts a random structure containing small domains of a (√7×√7)R19.1° reconstruction.

The interaction of C60 with the (2×2) and (1×1)LT reconstructions of the GaAs(111)B surface has been studied using synchrotron radiation core-level and valence band photoemission. For the (2×2) phase, C60 adsorption produces no change in either the line-shape or the energy position of the Ga3d and As3d core-levels. In contrast, the As3d photoelectron spectrum of the (1×1)LT surface is considerably altered following the deposition of C60. Our results indicate that the character of C60 adsorption may be changed from physisorption to chemisorption via variations in surface reconstruction and stoichiometry.

The (111)B surface of GaAs has been investigated using scanning tunneling microscopy (STM) and a number of different reconstructions have been found at different surface stoichiometries. In accordance with electron diffraction studies, we find the series (2 × 2), (1 × 1)LT, (19 × 19) and (1 × 1)HT with increasing annealing temperature, corresponding to decreasing surface As concentration. The (1 × 1)LT is of particular interest, since it only occurs in a narrow temperature window between the two more established reconstructions, the (2 × 2) and the (19 × 19). We find the (1 × 1)LT to take the form of a mixture of the local structures of both the (2 × 2) and (19 × 19) phases, rather than having a distinct structure. This is behaviour consistent with a kinetically limited system, dominated by the supply of As adatoms to the surface, and may be an example of a continuous phase transition. Above the (1 × 1)LT transition, atomic resolution images of the (19 × 19) surface reveal only a three-fold symmetry of the hexagonal structural units, brought about by inequivalent surface bonding due to the 23.4° rotation of the surface unit cell relative to the substrate. This is responsible for the disorder found in the (19 × 19) reconstruction, since the structure may form in one of two domains. At lower surface As concentration, the (1 × 1)HT surface adopts a structure combining small domains of a (7 × 7)R 19.1° structure and random disorder. There is no apparent similarity between the (1 × 1)LT and (1 × 1)HT structures, which may be due to our measurements being conducted at room temperature and without an As flux to control the surface As concentration.

The surface structures resulting from the deposition of Sb on the GaAs(111)B-(2 × 2) surface at room temperature followed by annealing, have been studied by high-resolution soft X-ray photoemission (SXPS) and low energy electron diffraction (LEED). For depositions at room temperature with no subsequent anneal and for annealing temperatures up to 300°C, Sb islands are formed between which the As trimer-based (2 × 2) substrate reconstruction of the clean GaAs surface is observed. Annealing to temperatures between 350 and 475°C leads to the creation of Sb chain pairs coexisting with regions of Sb trimers. At 500°C an ordered surface is produced, associated with Sb trimers and an As vacancy.

N-type ZnSe thin films have been grown by MBE on GaAs (001) surfaces and capped with an amorphous selenium layer. The Se cap was thermally desorbed under ultrahigh vacuum to recover the (2 × 1) and c(2 × 2) reconstructed surfaces. Selected metal contact formation was monitored using core and valence level photoelectron emission spectroscopy by in-situ exposure of the surface to heated sources of Au, Ag and Pb. In each case, lineshape analysis of emission spectra indicated a low level of interfacial mixing and provided an insight into the metal layer growth model. Both Au and Ag were found to grow in closely spaced islands of approximately equal height. The morphology of Au and Ag layers was confirmed by cross-sectional transmission electron microscopy. Monitoring of core and valence level emission peak positions allowed the determination of the metal-n-ZnSe Schottky barrier height, for a sufficiently thick metallic layer. Measurements on this wide-gap semiconductor, even at 300 K, were influenced by the presence of a surface photovoltage, which could be identified and subtracted for a fully-formed metallic layer. The n-type ZnSe Schottky barrier heights inferred from the relative Fermi level shifts (ΦBN(Au) = 1.74 eV, ΦBN(Ag) = 1.47 eV and ΦBN(Pb) = 1.25 eV), were found to scale with the metal work function for these three unreactive interfaces.

We present the first in-situ spot profile analysis low energy electron diffraction (SPA-LEED) study of the MBE growth of sub-monolayer coverages (0 to 1 ML) of Si on GaAs(001). Changes in the surface reconstructions from c(4 × 4) via mixed c(4 × 4)/(1 × 2), (1 × 2)/(2 × 1), (1 × 2)/asymmetric (3 × 1) and asymmetric (3 × 1) to a (3 × 1) increasing Si coverage have been monitored. Results are subsequently compared with recent in-situ reflection high energy electron diffraction (RHEED) and scanning tunnelling microscopy (STM) measurements. The continuous splitting between the 13- and 23-order diffraction spots up to the completion of the symmetric (3 × 1) reconstruction has been examin detail. Domain sizes for each reconstruction have been quantified from the spot profiles.

The techniques of reflectance anisotropy spectroscopy (RAS) also termed reflectance difference spectroscopy (RDS) and reflection high-energy electron diffraction (RHEED) have been employed to characterise the growth of submonolayer coverages (0.005 to 1.000 monolayer (ML)) of Be deposited onto the GaAs(001)-c(4 × 4) and (2 × 4)-β surfaces. The following series of surface reconstructions evolved with increasing Be coverages from 0 to 1 ML: GaAs(001)-c(4 × 4) → c(4 × 4)(1 × 2) → c(4 × 4)(1 × 3) → (1 × 2)(1 × 3) → (1 × 3) → (1 × 2); and, GaAs(001)-(2 × 4)-β → (2 × 4)(1 × 3) → (2 × 1)(1 × 3) → (1 × 2). The fact that unique, but highly reproducible, RAS signatures were obtained for each of these surface phases demonstrates the applicability of a combined RAS/RHEED system for monitoring sub-monolayer heteroepitaxial growth with a surface sensitivity of the order of 1100th of a monolayer.

The alkali-metal/III–V semiconductor interface is a model system with which to study overlayer metallization and Schottky barrier development. Until now, typically the cleaved (110) surfaces of the semiconductor have been utilized in this respect, though in this work we have used the Ga-vacancy (2 × 2) reconstructed surface of GaAs(111)A as the starting surface. This surface is known to exhibit many similarities with the cleaved (110) surface, due to the separation of empty and filled dangling bonds onto the Ga and As surface atoms respectively. We have found through using soft X-ray photoemission from both core-level and valence-band features that the interface is remarkably unreactive, with almost no change in the Ga 3d lineshape with Na deposition at low temperatures. With regard to the growth-mode, work-function variation and band-bending however, the behaviour is close to that found for the cleaved surface. The onset of the Na LVV Auger transition only occurs after metallization begins and is consistent with ionic bonding to the substrate, though the substrate core-level development points to a reduced charge transfer with respect to the (110) surface.

The (2 × 4) reconstruction of the (001) surface of GaAs has been studied using scanning tunnelling microscopy (STM) and spectroscopy. The images, produced at several biases, show coexisting two dimer and three dimer surface unit cell reconstructions. By examining line profiles across the dimers, we find an asymmetry in the two dimer surface unit cell reconstruction which changes with the sample bias. The images of the three dimer surface unit cell reconstruction are also shown to be different at different biases. A spectroscopic spectrum is presented which gives insight into the origin and characteristics of negative and positive bias tunnelling. Our results are compared to theoretical studies of the expected appearance of STM images under different bias conditions and the implications of the findings are discussed.

Reflectance anisotropy spectroscopy (RAS) in combination with reflection high-energy electron diffraction (RHEED) was used to study in situ the initial steps of molecular beam epitaxial growth of InAs on GaAs(001). Due to the large lattice mismatch InAs is known to grow in Stranski–Krastanov mode leading to the formation of quantum dots after the transition from two- to three-dimensional growth mode. In this article the precise determination of the growth mode transition and the subsequent development of the islands have been of particular interest. During the growth of the two-dimensional InAs layer, the RHEED-pattern changed from the c(4×4) of the clean GaAs to a (1×3) surface reconstruction. Accordingly, the RAS-spectra, taken every 0.2 ML, indicate changes of the As-dimer configuration. At 1.8 ML (spotty RHEED-pattern) a saturation of the intensity of the dimer related RAS-signal around 2.6 eV was found. The relaxation of the InAs layer and the formation of the quantum dots was followed by time-resolved RAS at 2.6 and 4 eV. It is shown here, that the time constant of this process, the thickness of the InAs wetting layer and the equilibrium morphology of the islands are strongly temperature dependent. The remaining equilibrium InAs wetting layer thickness at the surface was estimated to be about 1 ML (0.8 ML at 625 K and 1.2 ML at 725 K).

As-terminated Si surfaces are model semiconductor interface systems with a wide range of technological applications. We have studied As-terminated Si (001) surfaces with scanning tunneling microscopy which reveals that it is possible to produce a well ordered surface. Some characteristic types of defects do occur on this surface, however, which are found to be of particular interest. These include antiphase domain boundaries, step edges, and long, atomically straight trenches running perpendicular to the dimer rows across the surface. The nature and origin of these defects are discussed.

Reflectance anisotropy spectroscopy (RAS) has been employed to characterize the overlayer growth of GaAs onto sub to one monolayer coverages of Si δ layers deposited on the GaAs(001)-c(4×4) surface. The low growth temperature (400 °C), required to avoid spreading of the dopant away from the δ plane, has meant that the study of a RAS feature related to the linear electro-optic (LEO) effect is complicated by disordering at the GaAs surface. This disordering is induced not only by the growth temperature, but also by the presence of the Si δ layer itself. Variable thickness studies indicate that the LEO-induced signal is dependent on the field profile in the surface layer. It has been observed that the intensity of the LEO feature, as a function of Si coverage, reaches a maximum at ∼0.01 ML (∼6.4×1012 atoms cm−2) in agreement with previous studies of the site occupancy of Si δ layers.

The alkali-metal/III–V semiconductor interface is a model system with which to study overlayer metallization and Schottky barrier development. Until now, typically the cleaved (110) surfaces of the semiconductor have been utilized in this respect, though in this work we have used the Ga-vacancy (2 × 2) reconstructed surface of GaAs(111)A as the starting surface. This surface is known to exhibit many similarities with the cleaved (110) surface, due to the separation of empty and filled dangling bonds onto the Ga and As surface atoms respectively. We have found through using soft X-ray photoemission from both core-level and valence-band features that the interface is remarkably unreactive, with almost no change in the Ga 3d lineshape with Na deposition at low temperatures. With regard to the growth-mode, work-function variation and band-bending however, the behaviour is close to that found for the cleaved surface. The onset of the Na LVV Auger transition only occurs after metallization begins and is consistent with ionic bonding to the substrate, though the substrate core-level development points to a reduced charge transfer with respect to the (110) surface.

The surface structures resulting from the deposition of various coverages of Sb on the GaAs(111)B-(2×2) surface at room temperature, followed by annealing in the 100–375 °C temperature range, have been investigated using scanning tunneling microscopy. At low annealing temperatures Sb islands are observed displaying no ordered atomic structure, between which the As trimer based (2×2) reconstruction of the clean GaAs surface is visible. Annealing above 250 °C causes the formation of Sb trimers which are distinguishable from the remaining As trimers via contrast differences in filled- and empty-state images. Annealing at still higher temperatures leads to the creation of Sb chain pairs oriented along the substrate 〈110〉 directions, coexisting with regions of Sb trimer based reconstruction between the chain pairs. The local periodicity of the patterns of Sb trimers between the chain pairs is dependent on the separation between chain pairs.

We present scanning tunneling microscopy data illustrating the evolution of the decapped GaAs(001) surface following annealing in stages from 450 to 540 °C. After annealing at 450 °C a (2×4) reconstruction is formed by kinked rows of two As dimer unit cells. Following annealing in the 475–500 °C range small isolated regions of (4×2) reconstruction are visible, with a considerable increase in disorder of the remaining (2×4) reconstructed areas. Annealing at higher temperatures causes the (4×2) structure to become increasingly dominant. We have noted significant differences in the surface morphology as a function of annealing time. Our images of the (4×2) surface are similar to those recently reported by other groups but we propose a new structural model.

Summary form only given. InGaAs/GaAs strained-layer quantum well structures grown on non-(001) oriented substrates are of fundamental interest for a variety of nonlinear optical elements. We have studied the low-temperature photoluminescence of InGaAs/GaAs (111)B single quantum well structures with 25% Indium mole fraction. The combination of band-gap narrowing and screening of the internal fields leads to complex-carrier-induced nonlinearities in this piezoelectric system.