摘要:

A detailed study of near‐gap photoluminescence (PL) from strained Si1−xGexalloy layers (x=0.01–0.05) and Si/Si0.95Ge0.05multi‐quantum‐wells (MQWs) has failed to show either free‐ or dopant‐bound excitons in as‐molecular‐beam‐epitaxy‐prepared epitaxial layers. Low‐temperature PL was, however, successfully induced in these same heterostructures by the selective introduction of relatively shallow radiation‐damage bound‐exciton centers,I1andG(137 and 186 meV deep, respectively). TheI1center, in particular, produced broadened spectra which are shown clearly to emanate from the epitaxial layers, with separate and distinguishable components originating from both the Si and the Si1−xGex(x=0.01–0.05) layers. This is among the first such reports of luminescence verifiably originating from within a Si/Si1−xGexmultiple heterostructure. Importantly, we find that this defect‐induced PL is not significantly diminished (or even significantly influenced) by the addition of multiple heterointerfaces, thus leading to the conclusion that heterointerface quality may be good. This indicates that these heterointerfaces are not the source of the competing nonradiative recombination which likely prevents the observation of near‐gap PL, which is instead possibly due to bulk defects.

ISSN:0734-211X    

DOI:10.1116/1.585708

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The electronic structure of the materials being measured has a strong effect on the spectroscopy of the interface between them measured by ballistic electron emission microscopy (BEEM). Specific calculations for CoSi2/Si(111) and NiSi2/Si(111) based on the calculated band structures of the materials illustrate some of the observable effects due to band structures, particularly of the overlayer. The BEEM spectra for CoSi2/Si(111) show a delayed onset due to a mismatch of the states near the conduction band minimum in the Si. The spectra for NiSi2/Si(111) show structure due to a decrease in the density of states in the NiSi2at ∼1.8 eV above the Fermi level.

ISSN:0734-211X    

DOI:10.1116/1.585709

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

A semiclassical screening theory for semiconductors is used to treat the image potential throughout a one‐dimensional metal‐vacuum‐semiconductor junction in the absence of surface states. The image interaction due to induced surface charge at the semiconductor‐vacuum interface produces an effective band bending in the semiconductor interior, whose influence on electron tunneling through the junction is investigated. In particular, we examine the effect of this extra potential on STM measurements of the apparent tunneling barrier at unpinned semiconductor surfaces, and considern‐type, H‐terminated Si(111) as a specific example. In the instance where tip‐induced band bending may be neglected, we find the role of the image potential in metal‐vacuum semiconductor tunneling to be qualitatively similar to its role in metal‐vacuum‐metal tunneling: The experimentally determined barrier height—obtained from the logarithmic derivative of the tunneling current with respect to tip–sample separation—deviates little from the electron affinity of the semiconductor, while the theoretical barrier height exhibits a stronger dependence on the vacuum gap width. The origin of this behavior appears to lie in the fact that while the image interaction in the semiconductor may be long range, the image induced tunneling barrier is not.

ISSN:0734-211X    

DOI:10.1116/1.585710

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

We report on a calculation of transport in InAs/GaSb/AlSb‐based interband tunnel structures using a realistic band structure model. The results are compared with calculations using a two‐band model which includes only the lowest conduction band and the light‐hole band. We find that for device structures containing GaSb quantum wells, the inclusion of heavy‐hole states can introduce additional transmission resonances and substantial hole‐mixing effects. These effects are found to have a significant influence on the current–voltage characteristics of interband devices.

ISSN:0734-211X    

DOI:10.1116/1.585711

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

We have investigated the first in a series of compositionally graded quasi‐insulator/semiconductor heterojunction (HJ) capacitors, intended to provide low interface state densities, low dc leakage currents, and high effective surface barriers. Molecular‐beam epitaxy (MBE) was used to grow compositionally graded InxAl1−xAs quasi‐insulators withx≤0.52 deposited on semiconducting In0.53Ga0.47As layers lattice matched ton+‐InP substrates. Interface states derived from electric field and temperature‐dependent capacitance‐voltage measurements have densities in the order of ≊1011/cm2 eV and have time constant distributions which are strongly dependent on compositional gradient. The surface barrier height also depends on the compositional gradient and the leakage current is decreased by three orders of magnitude from 10−6to 10−9A for a reverse bias of 1 V. Heterojunction insulated gate field‐effect transistors (HIGFETs) with an intrinsic transconductancegm=125 mS/mm were obtained on a 5‐μm‐long gate structure.

ISSN:0734-211X    

DOI:10.1116/1.585712

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

First‐principles total‐energy calculations are used to study the structure of As overlayers deposited on a stepped Si(100) surface. It is predicted that deposition of As at low substrate temperatures allows the As to grow directly on top of the Si surface, while growth at high temperatures results in a rearrangement of the surface as if the As replaced the original top Si layer. This result explains the sublattice orientation dilemma in GaAs‐on‐Si epitaxy.

ISSN:0734-211X    

DOI:10.1116/1.585714

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Surface composition is known to influence cation and anion incorporation rates during III–V molecular‐beam epitaxy (MBE). [See, for example, Van Hove and Cohen, Appl. Phys. Lett.47, 726 (1985).] Thus, incorporation rates are expected to vary at heterointerfaces. The details of how incorporation rates vary in time during heterointerface formation are of interest because they completely determine resulting compositional profiles and/or layer thicknesses. In this study desorption mass spectrometry is used to determine the time dependence of incorporation rates during MBE growth of III–V heterostructures, with an emphasis on the heterointerface formation process. Under many conditions incorporation rates are found to vary in a nonsteplike manner, resulting in nonsteplike compositional profiles. Three different heterointerfaces are investigated: AlGaAs on GaAs, GaInAs on GaAs, and GaAsSb on GaAs. At growth temperatures for which significant Ga desorption occurs, AlGaAs on GaAs interfaces are found to be enriched in Al content relative to adjacent AlGaAs. In addition, transients are observed in the Ga desorption rate which suggest the occurrence of an Al–Ga displacement reaction. When Sb desorption is significant, GaAsSb on GaAs interfaces are found to be enriched in Sb content relative to adjacent GaAsSb. And when In desorption is significant, GaInAs on GaAs interfaces are found to be enriched in In content relative to adjacent GaInAs. The latter result is verified by x‐ray and photoluminescence measurements on separately grown, narrow, single GaInAs/GaAs quantum wells. Compositional grading for each system investigated is found to occur over a distance of about two to four monolayers. These results are shown to be consistent with a model which assumes simple first order desorption behavior and which incorporates strain‐dependent activation energies for desorption.

ISSN:0734-211X    

DOI:10.1116/1.585715

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

FeSi2films grown in ultrahigh vacuum on Si (111) substrates by solid phase epitaxy (SPE) have been characterized by severalinsituandexsitustructural techniques: reflection high‐energy electron diffraction (RHEED), x‐ray diffraction (XRD), and Rutherford backscattering (RBS). The results on a film a few hundred angstroms thick confirm that the FeSi2which forms in these conditions is the semiconducting β phase and that an epitaxial growth takes place with the (202) and/or (220) FeSi2planes parallel to the Si (111) planes. The lattice mismatch measurements in films as thin as 100 Å indicate that the films are little or no elastically strained, at least at a FeSi2growth temperature of 600 °C.

ISSN:0734-211X    

DOI:10.1116/1.585716

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

We have studied the growth of Fe and Co films on ZnSe(001) epilayers and GaAs(001) bulk substrates with electron forward scattering in the form of Auger electron diffraction (AED), and with x‐ray photoelectron spectroscopy (XPS) and reflection high energy electron diffraction to determine the mode of film growth and the formation of the interface. The coverage dependence of the AED forward scattering peaks is modeled and compared with the experimental data obtained for these overlayer systems. We find that the growth of Fe on ZnSe(001) at 175 °C proceeds in a predominantly layer‐by‐layer fashion, while a more three‐dimensional growth mode occurs on the oxide‐desorbed GaAs(001) substrate for both Fe and Co overlayers. Deposition of Co on the ZnSe(001) epilayers results in poorly ordered multicrystalline growth. The XPS data show that the metal/ZnSe interface is less reactive than the corresponding interface with the GaAs(001) substrate.

ISSN:0734-211X    

DOI:10.1116/1.585717

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The spontaneous change of growth orientation during the molecular beam epitaxy of In0.5Ga0.5P/GaAs superlattices is investigated as a function of the growth temperature by cross‐sectional transmission electron microscopy. It is observed that there exists a critical temperature above which a change in growth orientation from 〈100〉 to 〈311〉 occurs and is characterized by the evolution of V‐shaped grooves with {311} facets. Further increase in the temperature enhances the evolution of the {311} facets. It is found that the formation of the V‐shaped grooves is along the [01̄1] direction and that the most critical stage for the change in orientation is the interruption after the growth of the GaAs layer with P2flux. Based on these observations the atomic arrangement on a stable (311) surface resulting from the spontaneous change of the growth orientation is discussed.

ISSN:0734-211X    

DOI:10.1116/1.585718

出版商:American Vacuum Society    

年代:1991

数据来源: AIP