摘要:

We present a Raman scattering study of ultrathin SiGe superlattices. The spectra show evidence for the formation of superlattice structures with disordered interfaces. We explain the Raman peak energies in terms of strain and confinement effects and present a simple model for the Raman spectrum, from which we obtain semiquantitative information on the degree of superlattice ordering.

ISSN:0734-211X    

DOI:10.1116/1.584254

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

We calculate the electronic structure of geometrically ideal interfaces between column III metals and silicon. For a single neutral adatom the associated metallic Fermi energy must lie between the energy (0,+), for the removal of an electron, and the energy (0,−), for adding an electron, but is otherwise unrestricted. This circumstance also holds for many uncoupled adatoms and will produce pinning if the (0,+) and (0,−) levels are in the gap and the semiconductor Fermi energy is outside this range. At still larger coverages the occupied (0,+) levels and the (0,−) levels shift and broaden in energy until the gap between them disappears, pinningn‐type andp‐type semiconductors at the same energy. We find that the (0,+) level for a single aluminum adatom is in the silicon gap and that the (0,−) level is in the conduction band. In addition, the (0,+) level moves towards the valence band maximum as the metal coverage is increased.

ISSN:0734-211X    

DOI:10.1116/1.584256

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

We have studied the interface formation of Ni overlayers on cubic SiC(100) by photoemission spectroscopy with synchrotron radiation in the energy rangehν=40–140 eV. At room temperature deposition, Ni initially reacts with SiC and forms NiSi. At a nominal coverage of ∼20 Å Ni, the overlayer is metallic and the valence band spectra are identical to that of bulk Ni. The Ni/SiC(100) system is thermally stable up to ∼600 °C. The Ni overlayer reacts with the substrate to form Ni2Si at ∼800 °C. The reacted layer is inhomogeneous and consists of a mixture of SiC and Ni2Si. The reaction of Ni with SiC is quite different than that of Ni with the (111) surface of bulk Si. Ni reacts with Si(111) at 400 °C to form an epitaxial overlayer of the more Si‐rich silicide NiSi2.

ISSN:0734-211X    

DOI:10.1116/1.584257

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

Soft x‐ray photoelectron spectroscopy has been used to compare the chemistry of Al/InP(110) and Al/GaSe interfaces at room and low (<120 K) temperatures. For Al/InP(110) at low temperature it was found that the reacted feature of the In 4dspectrum has a coverage dependent binding energy. This is a result of the altered growth mode of the reacted In atoms on the low‐temperature surface. The spectral weight of the reacted feature is shown to be equivalent at the two temperatures, but escape depth effects imply that some reduction in reactivity has occurred. The behavior of the Al/GaSe interface is quite different. At low temperature no evidence for reaction was found within the equivalent coverage range. These results are discussed within the cluster‐initiated exchange reaction model.

ISSN:0734-211X    

DOI:10.1116/1.584258

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

The room temperature formation of the Cs/InP interface has been studied with soft x‐ray core level photoemission spectroscopy. The line shape analysis of the Cs 4dcore level indicates that at submonolayer coverages Cs is bonded at both In and P sites. This is deduced from a large (1 to 0.55 eV) coverage‐dependent splitting of the Cs 4dinto two doublets. The broadening at coverages close to a monolayer is consistent with the growth of an out registry overlayer as observed before for the Cs/GaAs interface. The energy shift of the substrate core level spectra indicates that the interface Fermi level stabilizes at about 0.8 eV above the valence band maximum which corresponds to relatively large (small) band bending forn‐type (p‐type) InP(110). This result is unexpected due to the small work function of Cs. The line shape and intensity analysis of the spectra indicates the formation of a laterally uniform overlayer and the lack of any noticeable chemical reaction.

ISSN:0734-211X    

DOI:10.1116/1.584259

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

We introduce a technique of RHEED ‘‘rocking patterns’’ for measuring rod intensity profiles and show that a simple kinematic interpretation may be used to deduce bulk structural parameters for a thin film. This method is used to identify a pseudohexagonal ‘‘1×1’’ epitaxial layer in the Ni/Si(111) system that is a precursor to single phase B‐type (twinned) or A‐type (untwinned) NiSi2. This material is a highly defective NiSi2overlayer which we call NiSi2(A/B). The possible influence of the reconstructed Si(111) 7×7 substrate in generating the NiSi2(A/B) structure is described.

ISSN:0734-211X    

DOI:10.1116/1.584260

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

We present a theoretical study of the dynamics of photoexcited carriers in GaAs/GaAlAs quantum‐well structures. Both the effects of lattice heating and of the energy exchange between electrons and holes on the carrier relaxation are included. The dynamics of the nonequilibrium optical phonons is described by a kinetic equation for phonon wave packets that properly incorporates the effect of carrier confinement on the nonthermal lattice modes. The modifications of the phonons due to the layered lattice structure are not considered here. For the carriers, Fermi–Dirac distribution functions are used and the electron–hole interaction is included explicitly. Results of this approach are presented for different layer thicknesses and are compared with the results of a previous calculation by one of us for bulk GaAs to assess the effect of quantum confinement on the carrier cooling. Confinement in quantum–well structures is found to increase the carrier cooling rate as compared to bulk GaAs. The cooling rate also increases as the well gets narrower, in agreement with recent experimental observations.

ISSN:0734-211X    

DOI:10.1116/1.584261

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

We have carried out pseudopotential calculations of the electronic structure of a Si4Ge4(001) superlattice grown on a Si substrate. We show that a model in which the microscopic potential and the bond lengths in the Ge layer are bulklike can account for the transition energies and oscillator strengths of the optical spectra reported for this structure in the literature. This is achieved without invoking a breakdown of the translational symmetry and indirect transitions.

ISSN:0734-211X    

DOI:10.1116/1.584262

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

II–VI multilayer structures are eminently suitable for various optoelectronic devices covering from the infrared to the ultraviolet spectral range. We present a theoretical study of the band lineups at interfaces involving ZnS, ZnSe, ZnTe, CdTe, and HgTe based on the ‘‘model solid’’ theory. We also experimentally investigate the strains and band offsets in ZnSe/ZnSxSe1−xstrained‐layer superlattices, using Raman and photoluminescence spectroscopy. The conduction‐band offset at such interfaces is found to be small. Theoretical predictions for other interfaces include a large type‐II offset in ZnSe/ZnTe, and a small average valence‐band discontinuity in ZnTe/CdTe.

ISSN:0734-211X    

DOI:10.1116/1.584263

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

The ZnSe–ZnTe superlattices have attracted considerable attention as possible blue/green light emitters. Although these superlattices have been successfully fabricated and show intense photoluminescence, there are many basic issues about this system which still remain unresolved. The most important of them is the value of the valence band offset between ZnSe and ZnTe. We have studied the band structure of ZnSe–ZnTe superlattices. Our calculations are based on second orderk⋅ptheory and include the effects of strain and spin‐orbit splitting on the superlattice band structure. We have investigated the dependence of the superlattice band gap on the valence band offset. Based on the assumption that the photoluminescence from the superlattice corresponds to a bound exciton at a Te1isoelectronic center in ZnSe, we have fit the experimental photoluminescence data withk⋅ptheory to obtain the best value of the valence band offset. The value we find is 0.97±0.10 eV. Alternatively, assuming that the photoluminescence was due to band‐to‐band transitions we obtain a valence band offset of 1.20±0.13 eV. We have also calculated the superlattice band gap as a function of the constituent material layer thicknesses for the first valence band offset quoted. We expect these results to be important in gaining an understanding of the value of the valence band offset, and the nature of the photoluminescence from this system.

ISSN:0734-211X    

DOI:10.1116/1.584220

出版商:American Vacuum Society    

年代:1988

数据来源: AIP