摘要:

Reflectance anisotropy spectroscopy (RAS) in combination with reflection high‐energy electron diffraction (RHEED) was used to studyinsituthe 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 thec(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).

ISSN:0734-211X    

DOI:10.1116/1.589064

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

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 (∼6.4×1012atoms cm−2) in agreement with previous studies of the site occupancy of Si δ layers.

ISSN:0734-211X    

DOI:10.1116/1.589065

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Using reflectance‐difference spectroscopy, we determine surface‐induced optical anisotropy (SIOA) spectra of clean, hydrogenated, and oxidized (113) and vicinal (001) Si surfaces to obtain a better understanding of the origin of the optical response of surfaces and interfaces. Hydrogenation was performed either by etching in dilute HF or by exposing clean surfaces to atomic hydrogen. Hydrogenated and oxidized vicinal surfaces show energy‐derivativelike spectra that roughly scale with offcut angle, indicating step‐induced behavior, and exhibiting features near 3.4 and 4.2 eV, the threshold energies of the (E1,E0′) andE2interband critical points of bulk Si, respectively. The appearance of derivativelike line shapes indicates that bulk threshold energies become dichroic near the surface due to the surface‐induced modification of the potential, as supported by model calculations. However, direct integration yields dielectric functions somewhat different from bulk values, indicating that the surface affects the near‐surface dielectric function. SIOA spectra for clean surfaces are qualitatively different, exhibiting dielectric‐functionlike line shapes that appear to originate primarily from terraces, although indications of smaller derivativelike contributions are also found.

ISSN:0734-211X    

DOI:10.1116/1.589066

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Using anabinitio, nonlocal pseudopotential method, we have calculated the reflectance anisotropy spectrum for a particular model of the GaAs(001)c(4×4) reconstructed surface. Excellent agreement with experiment was obtained, supporting the chosen model. The reflectance anisotropy was found to originate from optical transitions between bulk like valence band states and surface states in the conduction band. The nature and distribution of the electronic states involved is discussed.

ISSN:0734-211X    

DOI:10.1116/1.589067

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Discrete dipole calculations of the double cell type have been used to study the anisotropic reflection at normal incidence of stepped Si(001̄) 2×1‐type surfaces. OnlyDB‐type steps have been used. The maximum of the anisotropy turns out to be in a direction rotated with respect to the principal axes, and the anisotropy itself depends strongly on terrace width. Further the crossed polarizer configuration is interesting for experimental work since it has no offset.

ISSN:0734-211X    

DOI:10.1116/1.589068

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Using the optical methods of reflection anisotropy spectroscopy, surface photovoltage spectroscopy, and contactless electroreflectance, we have conducted anexsituinvestigation of (a) the InP/In0.53Ga0.47As(001) heterojunction interface as a function of InP overlayer thickness (50–1000 nm) and (b) the surfaces ofn‐ andp‐doped In0.53Ga0.47As(001). All samples were fabricated by organometallic vapor phase epitaxy. The results from these optical probes make it possible to form a comprehensive quantitative picture of the InP/InGaAs heterojunction, including conduction and valence band offsets of 275 and 325 meV, respectively, as well as the (001) surface of InGaAs (surface Fermi level=200 mV from the conduction band edge).

ISSN:0734-211X    

DOI:10.1116/1.589069

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Silicon wafer bonding is achieved by joining two particle‐free silicon wafers and annealing to elevated temperatures (∼1100 °C). We have used multiple internal transmission infrared absorption spectroscopy to probe the interface between the wafers upon initial joining and also during subsequent annealing steps. For atomically flat hydrophobic wafers (H passivated), we observe a pronounced shift in the Si–H stretching frequency due to the physical interaction (van der Waals attraction) that occurs when the surfaces come into intimate contact. The hydrogen eventually disappears at high temperatures (1000 °C) and Si–Si bonds are formed between the two surfaces. For hydrophilic wafers (oxide passivated), we initially observe three to five monolayers of water at the interface (providing the initial attraction through H bonding), as well as the presence of hydroxyl groups that terminate the oxide at low temperature. Upon moderate heating (<400 °C), the water trapped at the interface dissociates and leads to the formation of additional oxide. Between 400 and 800 °C, the hydroxyl groups disappear, resulting in a corresponding increase in oxideandthe formation of Si–O–Si bridging linkages across the two surfaces.

ISSN:0734-211X    

DOI:10.1116/1.589070

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Strain, dislocations, and electrically active defects at and near the interface of Si/SiO2and Si/GaP heterostructures are analyzed by optical second‐harmonic spectroscopy. For plasma oxides deposited on Si(001) and Si(111), time‐dependent second‐harmonic experiments reveal that near‐interface oxide defects trap charge by the tunneling of photoexcited electrons from the Si conduction band. The space‐charge field‐induced second‐harmonic transients are resonantly enhanced by two‐photonE1transitions in silicon. In GaP epilayers grown on Si(001) the bulk dipole‐allowed electro‐optical effect is suppressed by the formation of antiphase domains. In contrast, in GaP films grown on Si(111) and vicinal Si(001) the density of antiphase domains is considerably reduced yielding an enhancement of the second‐order nonlinear optical response by two orders of magnitude.

ISSN:0734-211X    

DOI:10.1116/1.589071

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Imaging of topography, locally induced photoluminescence and Fermi‐level pinning in adjacent ordered and disordered domains on a cleaved GaInP sample is performed using a near‐field scanning optical microscope and scanning capacitance microscope at room temperature in air. Highly localized photoluminescence spectra obtained by the near‐field scanning optical microscope on these domains show spectral peaks at 680 nm (ordered) and 648 nm (disordered) GaInP. The near‐field scanning optical microscope and scanning capacitance microscope data confirm previously published data, indicating that the electronic surface structure of ordered GaInP is significantly different from that of disordered GaInP. Both approaches indicate that the Fermi‐level at the surface of ordered GaInP is pinned, while the Fermi‐level at the surface of disordered GaInP is not pinned. The size, structure, and position of the ordered and disordered domains observed by the near‐field scanning optical microscope and scanning capacitance microscope agree with those obtained by cathodoluminescence and Kelvin probe force microscopy.

ISSN:0734-211X    

DOI:10.1116/1.589072

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Applications of x‐ray magnetic circular dichroism (XMCD) to the study of magnetic materials are described. XMCD spectra can be used to quantitatively determine magnetic properties on an element‐specific basis. These spectra are also sensitive to the chemical state and environment of the element being probed. The dichroism effect can also be used to produce images of microscopic magnetic structures and domains. Third generation synchrotron light sources are well suited to these experiments. Current and planned facilities at the Advanced Light Source, the first of the new light sources in the U.S., are described, focusing on a new facility with specialized undulators which will directly produce high flux, high brightness beams of circularly polarized x‐rays. With new beamlines which have been optimized for either spectroscopy or microscopy, this facility will provide the capability to provide detailed information about magnetic materials.

ISSN:0734-211X    

DOI:10.1116/1.589073

出版商:American Vacuum Society    

年代:1996

数据来源: AIP