摘要:

Using Hellmann–Feynman molecular dynamics, one can calculate the atomic motion, equilibrium geometries, and electronic states for clusters of atoms on semiconductor surfaces. Here we report studies that were motivated by the scanning tunneling microscopy and spectroscopy observations of Feenstra and co‐workers. Although the geometries and electronic structures vary from one simulation to another, we typically find states in or near the upper part of the band gap for Sb, Bi, Au, and Sn on GaAs(110). The character of these states is rather complicated and geometry dependent, but they tend to be largely associated with the cluster and the surface Ga atoms. That is, they can be roughly viewed as split off from the Ga‐derived conduction bands by the perturbation resulting from the semiconductor–cluster bonding.

ISSN:0734-211X    

DOI:10.1116/1.584962

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

In general, techniques that monitor theinsitugrowth of semiconductor materials with electron diffraction [such as reflection high energy electron diffraction (RHEED)] provide no quantitative information about surface stoichiometry. However, sophisticated materials problems, such as heteroepitaxial systems, require such information. Here we demonstrate that the use of characteristic absences in the fractional order diffraction features in RHEED patterns provide detailed quantitative information for the molecular beam epitaxial growth of materials such as GaAs. It is expected that this approach will lead to the improvement of growth for such interface‐sensitive systems as resonant tunneling devices.

ISSN:0734-211X    

DOI:10.1116/1.584940

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

We have used x‐ray photoelectron spectroscopy to measure the valence band offsetinsitufor strained Si/Ge (100) heterojunctions and for AlSb/ZnTe (100) heterojunctions grown by molecular‐beam epitaxy. For the Si/Ge system, Si 2pand Ge 3dcore level to valence band edge binding energies and Si 2pto Ge 3dcore level energy separations were measured as functions of strain, and strain configurations in all samples were determined using x‐ray diffraction. Our measurements yield valence band offset values of 0.83±0.11 eV and 0.22±0.13 eV for Ge on Si (100) and Si on Ge (100), respectively. If we assume that the offset between the weighted averages of the light‐hole, heavy‐hole, and spin‐orbit valence bands in Si and Ge is independent of strain, we obtain a discontinuity in the average valence band edge of 0.49±0.13 eV. For the AlSb/ZnTe (100) heterojunction system, we obtain a value of −0.42±0.07 eV for the valence band offset. Our data also suggest that an intermediate compound, containing Al and Te, is formed at the AlSb/ZnTe (100) interface.

ISSN:0734-211X    

DOI:10.1116/1.584941

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

The long standing problem of determining band offsets at semiconductor interfaces is readdressed. We show that the valence‐band discontinuity can be extracted from a knowledge of the local density of states across the interface. This method can also be used to determine the band offsets in superlattice structures. The concept of band offsets in short period superlattices is examined. It is shown that this is intimately connected with the localization of bands in one or other of the superlattice constituents.

ISSN:0734-211X    

DOI:10.1116/1.584942

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

In optical experiments with laterally patterned modulation‐doped GaAs/AlGaAs quantum wells, we observe spatially separate confinement of electrons and holes to one‐dimensional quantum wires. We determine the one‐dimensional subband spacing and Fermi energy from inelastic light scattering and photoluminescence spectra. From these measurements we directly determine the one‐dimensional electron density.

ISSN:0734-211X    

DOI:10.1116/1.584943

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

We demonstrate that a quasi‐one‐dimensional quantum wire can, in principle, be produced at the crossing point of heterointerfaces. We show that the intersection of two accumulation layers, which are formed along separate heterointerfaces, realizes an ‘‘accumulation wire.’’ Our theoretical analysis yields potential distributions which possess confined electronic states in the vicinity of the point of intersection. In our design, confinement in the quantum wire is solely provided by the inherent electric fields associated with heterointerfaces without the need for additional lithography. In other words, our proposal of the quantum wire compares to previous designs in the same manner in which a quasi‐two‐dimensional (2D) system in an accumulation (or inversion) layer compares to a quasi‐2D system in a quantum well.

ISSN:0734-211X    

DOI:10.1116/1.584944

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

We have calculated the absorption strengths for intersubband transitions inn‐type Si1−xGex/Si superlattices. These transitions can be used for the detection of long‐wavelength infrared radiation. A significant advantage in Si1−xGex/Si superlattice detectors is the ability to detect normally incident light; in Ga1−xAlxAs/GaAs superlattices intersubband absorption is possible only if the incident light contains a polarization component in the growth direction of the superlattice. We present detailed calculations of absorption coefficients, and peak absorption wavelengths for [100], [111], and [110] Si1−xGex/Si superlattices. Peak absorption strengths of about 2000–6000 cm−1were obtained for typical sheet doping concentrations (≊1012cm−2). Absorption comparable to that in Ga1−xAlxAs/GaAs superlattice detectors, compatibility with existing Si technology, and the ability to detect normally incident light make these devices promising for future applications.

ISSN:0734-211X    

DOI:10.1116/1.584945

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

Using the double‐modulation extension of reflectance‐difference spectroscopy, we obtain surface dielectric anisotropy spectra under steady‐state conditions for several reconstructions encountered in molecular beam epitaxy on (001) GaAs and follow their evolution with temperature. The changes observed with temperature are gradual, generally not exhibiting distinct boundaries. Marked changes in anisotropy are observed during thermal desorption of the native oxide, indicating that the process is not simple but involves surface roughening.

ISSN:0734-211X    

DOI:10.1116/1.584946

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

The adsorption characteristics of bismuth and antimony on III–V(110) substrates have been studied as a function of overlayer coverage and deposition conditions using low energy electron diffraction (LEED). We examine the different roles of chemical bonding and atomic size for determining surface ordering phenomena and epitaxy in these systems. LEED and Auger data were collected for monolayer range film thicknesses prepared on GaAs, InP, GaSb, InAs, and InSb substrates cleavedinsitu. BothIVand diffraction spot profiles were measured. Our results indicate that significant differences exist between the structure and surface chemical bonding of antimony and bismuth to III–V materials which were not revealed from previous studies using GaAs alone.

ISSN:0734-211X    

DOI:10.1116/1.584947

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

The excitation intensity and temperature dependences of the photoluminescence (PL) from Ga0.52In0.48P grown by organometallic vapor phase epitaxy on GaAs substrates have been investigated as a function of the epilayer growth temperature and the substrate misorientation from (100). The energy band gap is dependent on substrate temperature during growth but is effectively independent of substrate misorientation. A strong excitation intensity dependence of the PL is found to be a function of both substrate orientation and growth temperature. We postulate that the strong dependence of PL emission energy on excitation intensity in some samples may result from the sizes, shapes, and orientations of ordered domains.

ISSN:0734-211X    

DOI:10.1116/1.584948

出版商:American Vacuum Society    

年代:1990

数据来源: AIP