摘要:

The centroid shifts of positron annihilation spectra are reported from the depletion regions of metal‐oxide‐semiconductor (MOS) capacitors at room temperature and at 35 K. The centroid shift measurement can be explained using the variation of the electric field strength and depletion layer thickness as a function of the applied gate bias. An estimate for the relevant MOS quantities is obtained by fitting the centroid shift versus beam energy data with a steady‐state diffusion‐annihilation equation and a derivative‐gaussian positron implantation profile. Inadequacy of the present analysis scheme is evident from the derived quantities and alternate methods are required for better predictions.

ISSN:0021-8979    

DOI:10.1063/1.350540

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We have grown HgTe/CdTe superlattices by molecular beam epitaxy; barrier thicknesses were in the range from 15 to 91 A˚ and the well thickness was maintained at a constant value of 30 A˚. The infrared photoluminescence was investigated by means of Fourier transform infrared spectroscopy in the temperature range from 4.2 to 300 K. All superlattices showed pronounced photoluminescence at temperatures up to 300 K. To gain more detailed insight into the band structure of the HgTe/CdTe superlattices, band structure calculations were performed. The concept of the envelope function approximation was followed. Employing the transfer matrix method, the calculations were completed taking into account an eight bandk⋅pmodel. An important parameter in these calculations is the natural valence band offset (VBO) between the well and barrier materials. As a general trend, the value for the direct gap decreases with increasing VBO. The experimentally determined energies of the band gap are in reasonable agreement with the values obtained by the theoretical calculations. A comparison between theory and experiment shows that the observed transition energies are closer to calculations employing a large offset (350 meV) as opposed to a small VBO (40 meV).

ISSN:0021-8979    

DOI:10.1063/1.351375

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We investigated luminescence characteristics of the (GaP)n(GaAs)natomic layer superlattices grown on the [001] GaAs substrate by pulsed jet epitaxy. In the single monolayer superlattice (n=1), only direct transition was observed at the whole range of measurement temperature and photoexcitation intensity. Both direct &Ggr;‐type and indirectX‐type emissions were observed in the indirect transition multimonolayer superlattices (n=2–4). These transitions were competitive. The direct emission was stronger at room temperature; however, the indirect emission was intense at low temperatures. This could be explained in terms of oscillator strength and thermal distribution of photoexcitation electrons into the &Ggr; andXlevels in the conduction band. Under high excitation, the direct emission increased superlinearly with the excitation intensity, but the indirect emission showed a saturation for its longer radiative recombination lifetime. We also observed the band‐to‐acceptor transition at the lower energy side of the indirect band‐to‐band transition. This acceptor was expected to be incorporated into the GaAs well layer during growth.

ISSN:0021-8979    

DOI:10.1063/1.350491

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We studied the light scattering spectra of three molecular beam epitaxy GaAs samples with Si‐&dgr; doping. A broad feature appears in these spectra which is similar to that attributed by other authors to resonant Raman scattering by electronic intersubband transitions. By studying the dependence of this emission on exciting laser photon energy we believe that this line is really produced by nonequilibrium luminescence at theE0+&Dgr;0gap.

ISSN:0021-8979    

DOI:10.1063/1.350492

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Carbon ion bombardment in the energy range of 20–500 eV, which occurs in reactive ion etching using alkanes, has been performed on InP with a mass‐separated carbon ion beam in an ultrahigh vacuum chamber. The sample structure consisted of an ultrathin, epitaxial InP (40 A˚) layer on InGaAs.Insitupolar‐angle dependent x‐ray photoelectron spectroscopy was used to measure sputtering, deposition on, and damage of the InP layer, and to determine if any damage had propagated to the underlying InGaAs. An investigation of damage removal was also carried out byinsituthermal annealing, and by exposure to ultraviolet radiation and ozone. It was found that carbon ion bombardment led to carbon incorporation and to a gross change in the surface composition of the semiconductor. A complex, heterogeneous In‐P‐C alloy was formed. Sputtering of InP and preferential removal of P were also evident. Further carbon ion bombardment resulted in the deposition of an amorphous carbon residue. The degree of residual damage increased with bombarding energies. At 20 eV, the damage was confined to the 40 A˚ InP layer, but at 100 eV, significant broadening of the As 3dpeak was observed, which suggests that the underlying InGaAs layer was also damaged at this higher energy. Bombardment with 500 eV ions caused severe damage to both the InP and InGaAs layers. Heating of the irradiated samples at 350 °C in vacuum was ineffective in annealing the damage, although a reduction of the surface Fermi level position from 0.95 to 0.75 eV (relative to the valence band maximum) was measured for 20 eV carbon ion bombarded samples. This is attributed to the acceptor behavior of the incorporated carbon. Exposure to ultraviolet light/ozone was also found to be ineffective in removing the carbon residue.

ISSN:0021-8979    

DOI:10.1063/1.350493

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

This work deals with the study of laser‐induced surface vaporization in the presence of an ambient gas, in the conditions where a plasma develops at the gas‐material interface. In the experiment, a pulsed CO2laser is focused onto a titanium target in a cell containing He, Ar, or N2from a few tenths of Torr up to atmospheric pressure. The temporal and spatial distributions of Ti atoms vaporized from the surface are measured by laser‐induced fluorescence spectroscopy. Strong evaporation is observed in helium up to several hundred Torr. In this gas, the Ti atom plume expands according to the propagation of a blast‐wave. On the contrary, a very small quantity of material is vaporized in the presence of Ar or N2, because a highly absorbing breakdown plasma develops in this case, as soon as the surface vaporization threshold is reached, shielding the target from subsequent laser heating. These results corroborate our previous analysis based on the spectroscopic observation of the plasma.

ISSN:0021-8979    

DOI:10.1063/1.350494

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Cadmium telluride (CdTe) and zinc telluride (ZnTe), direct gap semiconductors with room‐temperature band gap energies of 1.45 and 2.25 eV, respectively, form a continuous series of solid solutions (Cd1−xZnxTe). The band gap energy of Cd1−xZnxTe can be tailored in the 1.45–2.25 eV range. Cd1−xZnxTe with band gap energy of 1.65–1.75 eV is suitable as the upper member of a two‐cell tandem structure for the photovoltaic conversion of solar energy. In this work, polycrystalline films of Cd1−xZnxTe have been deposited on glass, CdS/SnO2:F/glass, and Cd1−xZnxS/SnO2:F/glass substrates at 400 °C by the reaction of dimethylcadmium (DMCd), diethlyzinc (DEZn), and diisopropyltellurium (DIPTe) in a hydrogen atmosphere. The composition of Cd1−xZnxTe films determined by wavelength dispersive spectroscopy and x‐ray diffraction has been correlated with the band gap energy deduced from the junction photovoltage spectroscopy and optical transmission. The structural and electrical properties of Cd0.7Zn0.3Te (band gap energy 1.70 eV) films have been evaluated. Thin film Cd0.7Zn0.3Te/CdS and Cd0.7Zn0.3Te/Cd0.7Zn0.3S heterojunctions have been prepared and characterized.

ISSN:0021-8979    

DOI:10.1063/1.350495

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The paper deals with structural, optical, and electrical properties ofa‐SiC:H anda‐SiC:H,F films prepared by rf sputtering of a silicon target in Ar+H2+CH4and Ar+H2+CF4gas mixtures, respectively. The comparison of the physical properties of the two different sets of the samples has been considered and the influence of hydrogen and/or fluorine incorporation is examined and discussed.

ISSN:0021-8979    

DOI:10.1063/1.350496

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Morphologies of Si surfaces treated with aqueous solutions of hydrofluoric acid (HF) and ammonium fluoride (NH4F) have been investigated using surface infrared spectroscopy. We confirm that HF‐treated Si(111) surfaces are terminated with a monohydride (Si—H), dihydride (Si—H2), and trihydride (Si–H3), whereas NH4F‐treated Si(111) surfaces are dominantly terminated with Si—H. For Si(100), treatment in NH4F produces a surface for which the dihydride mode is enhanced compared to HF treatment, suggesting that surface Si—Si bonds on Si(100) are readily cleaved in a NH4F solution to generate a dihydride Si. The effect of varying the HF concentration on the morphology of HF‐treated Si(100) surfaces is investigated. It is demonstrated that 5% HF treatment produces Si(100) surfaces which have a larger density of surface Si—Si bonds than 50% HF or 0.5% HF treatment.

ISSN:0021-8979    

DOI:10.1063/1.350497

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The behavior of the intermetallic A15 compound Nb3Au in the early stage of mechanical milling was studied. By following the degradation of the superconducting transition temperature and the increase of the lattice parameter as a function of milling time, it was found that Nb3Au exhibits atomic (chemical) disorder due to milling. A value for the ballistic jump frequency of the atoms was assessed. The behavior turns out to be very similar to that of Nb3Sn, although for long milling time Nb3Sn amorphizes, whereas Nb3Au transforms from the A15 structure to the bcc structure.

ISSN:0021-8979    

DOI:10.1063/1.350498

出版商:AIP    

年代:1992

数据来源: AIP