摘要:

Carrier transport and collection was investigated in strained Si1−xGex/Si(100) double quantum wells (QWs) separated by a Si barrier. Steady‐state photoluminescence (PL) revealed a clear spectral dominance switch of PL between the two QWs as the Si barrier was systematically varied. Time‐of‐flight luminescence spectroscopy was used to estimate the mean drift velocity of carriers in terms of the luminescence rise time difference between the two QWs. Carrier collection efficiency was found to be dependent on the well width, which was obtained from the luminescence intensity difference.

ISSN:0734-211X    

DOI:10.1116/1.587072

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Photoluminescence (PL) observation at room temperature is reported in strained Si1−xGex/Si multiple quantum wells (MQWs) grown by gas source Si molecular beam epitaxy. It was found that QW PL is enhanced when MQWs are arranged so that photogenerated carriers are trapped efficiently to QWs without significant loss. This was achieved by locating MQWs over the penetration depth of the excitation light. QW PL was found to develop with a power exponent of 1.8 for lower excitation. QW PL was observed at room temperature for MQW samples withxup to 0.69.

ISSN:0734-211X    

DOI:10.1116/1.587073

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

A novel way of integrating epitaxial Si and carbon (C) doping capabilities within an existing solid‐source III–V molecular beam epitaxy system by means of electron‐beam evaporation is reported. By significantly increasing the Si evaporation rate over conventional effusion cells, this technique offers apracticalway of growing high Si content (III–V)–Si alloys and superlattices. The use of GaAs–Si alloys with adjustable lattice constants for GaAs on Si growth with improved crystalline quality over previous methods is also demonstrated. Both uniform layer and delta‐doped C in GaAs (p‐type concentration up to the mid 1019/cm3range) are demonstrated with carrier mobility comparable to other doping sources. These extended capabilities should find wide applications ranging from material synthesis to III–V devices and technology.

ISSN:0734-211X    

DOI:10.1116/1.587074

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

The dependence on the substrate temperature and the flux rates of the behavior of impinging elemental Si and Ge fluxes on a SiO2surface, including SiO2etching and the deposition of polycrystalline Si and SiGe films, was investigated by using the solid source molecular beam epitaxy (MBE). Flux rates of the source beams and a substrate temperature were in the range of 1 to 5×1013atoms/cm2 s and 710–810 °C, respectively. Under these experimental conditions, the Ge flux was not individually effective to etch the SiO2, but contributed to etching the oxide layer with an accompanying Si flux. The critical flux of Si for SiO2etching at 740 °C was determined to be about 1×1013atoms/cm2 s.

ISSN:0734-211X    

DOI:10.1116/1.587075

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

A technique for atomic layer‐by‐layer epitaxy of cuprate superconductors and other complex oxides has been developed at Varian. The samples are engineered by stacking molecular layers of different compounds to assemble multilayers and superlattices, by adding or omitting atomic monolayers to create novel compounds, and by doping within specified atomic monolayers. Apart from manufacturing trilayer Josephson junctions withIcRn≳5 mV, this technique enables one to address fundamental issues such as the dimensionality of HTSC state, existence of long‐range proximity effects, occurrence of resonant tunneling etc., as well as to synthesize novel metastable HTSC compounds.

ISSN:0734-211X    

DOI:10.1116/1.587076

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

The stability of the atomic flux from effusion cells is essential for the application of molecular‐beam epitaxy (MBE) to new materials systems. In particular, the possible effects of oxygen background pressure on source stability have been a concern to those applying MBE to the growth of oxides, such as the highTcsuperconductors. We have studied the effects of oxygen exposure on the sublimation of the alkaline earth elements Mg, Ca, Sr, and Ba from effusion cells, using deposition rate measurements and quadrupole mass spectrometry. Sublimation of Mg, Ca, and Sr is suppressed exponentially by oxygen with a characteristic pressure comparable to the source equilibrium vapor pressure. Ba sublimation is increased linearly by oxygen background. A surprising finding is that immediately after an exposure to oxygen, Mg, Ca, or Sr flux from an effusion cell is increased over a period of several minutes. We suggest an explanation for this phenomenon in terms of changes in the emissivity of oxide coated source material. The implication is that the stability of these sources isbetterat moderate oxygen pressures than at low oxygen pressures.

ISSN:0734-211X    

DOI:10.1116/1.587036

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

The morphology of molecular‐beam epitaxy (MBE) grown GaAs/NiAl/GaAs structures using scanning tunneling microscopy (STM) was investigated. Improving the flatness of the NiAl layer is achieved by improving the wettability of NiAl on GaAs by using a Ni template and increasing the island density by low‐temperature growth. This method gives a continuous, flat NiAl film with a mean roughness of one monolayer. A GaAs overlayer with a roughness of two monolayers or less is obtainable by using low‐temperature migration enhanced epitaxy (MEE).

ISSN:0734-211X    

DOI:10.1116/1.587037

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

The first observation of lattice images of stabilized α‐Sn grown at 150 °C by high‐resolution transmission electron microscopy is reported here. A structure of CdTe/α‐Sn/InSb has been grown on an InSb buffer layer, which was grown on an InSb(100) substrate by molecular beam epitaxy at 220 °C. During the growth, cross doping was carefully avoided. In addition, by the energy‐dispersive x‐ray spectroscopy, it was found that the interdiffusion of In and Te, which usually occurs across the interface of CdTe/InSb, is prevented by the α‐Sn layer inserted at the interface.

ISSN:0734-211X    

DOI:10.1116/1.587038

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Wurtzitic single‐crystal GaN and polycrystalline (columnar) InGaN have been grown on the Si(111) face in an electron cyclotron resonance plasma‐assisted molecular beam epitaxy process. Reflection high‐energy electron diffraction shows registry of the nitride basal‐plane triangular lattice with respect to the Si(111) substrate triangular network. Plan‐view transmission electron microscopy images reveal crystalline or polycrystalline GaN structure depending on growth temperature. High‐resolution x‐ray rocking curves of the (0002) peak were as narrow as 30 min for a 0.6‐μm GaN film grown on a thin AlN buffer layer at 750 °C.

ISSN:0734-211X    

DOI:10.1116/1.587039

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Carbon‐doped GaAs films have been grown by molecular‐beam epitaxy using carbon tetrabromide as the carbon source. The films were doped up to 1.3 × 1020cm−3with mobilities which compare favorably to beryllium‐doped films. Secondary‐ion mass spectrometry measurements made on these films indicate sharp transitions and negligible memory effects as well as near unity doping incorporation. Room temperature photoluminescence intensities were equivalent to comparably beryllium‐doped films at 5.0 × 1019cm−3. Photoluminescence intensities and hole concentrations were found to be dependent on both arsenic to gallium flux ratios and substrate temperature. Annealing studies on a film doped with carbon at 4.6 × 1019cm−3indicate good thermal stability of the carbon in the arsenic lattice site.

ISSN:0734-211X    

DOI:10.1116/1.587040

出版商:American Vacuum Society    

年代:1994

数据来源: AIP