摘要:

High concentrations of electrically active phosphorus have been grown in Si epitaxial layers at 750 °C and below in an atmospheric pressure deposition system using PH3and SiCl2H2in H2. PH3remarkably enhances the silicon deposition rate in the range 550–750 °C in contrast to previously reported doping studies using SiH4. Chemical concentrations as high as 2.5×1020 cm−3with an electrical activity of 1×1020 cm−3were obtained in layers that were free of defects by transmission electron microscopy. The doping level can be modulated between 1×1019and 5×1016 cm−3indicating that there are no complications due to dopant retention on sample or reactor wall surfaces. Emitter‐base diodes formed in the epitaxial layers exhibited ideal forward and low‐leakage reverse characteristics.

ISSN:0003-6951    

DOI:10.1063/1.105066

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The selective removal of epitaxial Si0.7Ge0.3from {100} silicon using an aqueous based etch is reported. An etch consisting of HNO3:H2O:HF(0.5%), 40:20:5 at 22 °C, removes Si0.7Ge0.3at a rate of 207 A˚/min, and removes {100} Si at a rate of 16 A˚/min. This corresponds to a selectivity of 1321 where the selectivity is defined as the ratio of the Si0.7Ge0.3to {100} Si etch rates. This etch leaves the surface smooth and free from pitting or trenching as observed by optical microscopy. The results obtained are consistent with a germanium enhanced oxidation mechanism of the Si0.7Ge0.3alloy during semiconductor removal.

ISSN:0003-6951    

DOI:10.1063/1.105067

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We present results on the picosecond dynamics of spin relaxation and thermalization of excitons in GaAs quantum wells. The spin relaxation time constant is ≊50 ps for resonant excitation and less than 10 ps for nonresonant excitation, considerably shorter than those for free electrons in the bulk. Photoexcited cold, nonthermal excitons thermalize in ≊50 ps at 10 K and less than 10 ps at 35 K. Exciton‐acoustic phonon energy exchange rates are determined from these measurements.

ISSN:0003-6951    

DOI:10.1063/1.105068

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The highest mobility InSb epilayer grown to date by organometallic vapor phase epitaxy has been achieved by utilizing high‐purity organometallic sources, choosing a reactor geometry to reproducibly control the source concentrations above the substrate, and using a high‐ integrity reactor system. On ap‐type InSb substrate, an unintentionally doped layer had a 77 Kn‐type carrier concentration and mobility of 1.4×1015cm−3and 2.53×105cm2/V s. Growths on GaAs substrates were greatly affected by the lattice mismatch and had 77 K carrier concentrations similar to the InSb case but with mobilities of (5.0–9.0)×104cm2/V s. The crystal quality, morphology, and cyclotron resonance characteristics are reported and found to be comparable to state‐of‐the‐art molecular beam epitaxy layers.

ISSN:0003-6951    

DOI:10.1063/1.105069

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Detailed studies of infrared absorption in nominally undoped and boron‐doped, free‐standing diamond thin films are reported. Difference measurements reveal absorption at 1300 cm−1(0.16 eV) due to boron‐induced single phonon, vibronic excitations. A relatively sharp peak at about 2420 cm−1(0.30 eV), a stronger, broader band centered at 3060 cm−1(0.38 eV), and a weak, broad peak at 4200 cm−1(0.52 eV), are identified as electronic transitions, with or without phonon assistance, of the boron acceptor. These results provide important confirmation of the hitherto presumed substitutional nature of boron doping and recent suggestions concerning electronic transport mechanisms in diamond thin films.

ISSN:0003-6951    

DOI:10.1063/1.105070

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

In this letter a relation is derived between hot isostatic pressing (HIP) temperature, the initial oxygen concentration of sintered Y‐Ba‐Cu‐O powder, the relative density, the oxygen pressure, and the oxygen concentration during HIP densification. The maximum attainable relative density is calculated as a function of HIP pressure. It turns out that degassing oxygen during HIP densification processing has considerable effects on densification maps. Using corrected and modified densification maps a recipe for manufacturing highly dense YBa2Cu3O7−xis presented.

ISSN:0003-6951    

DOI:10.1063/1.105071

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The Mo¨ssbauer effect of the 37.2 keV &ggr; transition of121Sb has been employed to study the electronic configuration of Sb ions in BaBi1−xSbxO3withx=0.2, 0.4, and 0.5. A single resonance absorption line is observed. The isomer shift changes slightly with Sb content and falls in the region corresponding to an Sb(V) valence state. The isomer shift of 7.6 mm/s is significantly depressed (∼1 mm/s) relative to its value in a typical Sb(V)O6chromophore and indicates a high degree of covalency, corresponding to significant 5sm5pnhybridization.

ISSN:0003-6951    

DOI:10.1063/1.105072

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A simple processing technique for preparation ofc‐axis‐oriented Bi‐Pb‐Sr‐Ca‐Cu‐O thin films is reported. ∼3000‐A˚‐thick superconductor films on silver substrate have been obtained by heavy cold rolling and partial melt processing of the superconductor‐silver composite structure. The films are highly textured due to the interface‐induced, layer‐like growth of the superconducting phase, and are essentially free of weak links. They exhibitedTc∼80 K andJc(4.2 K) ∼104–105A/cm2. This technique, which does not require epitaxial growth from single‐crystal substrates, may be suitable for high‐speed, low‐cost production of large‐area thin films, and points to other novel thin‐film processing possibilities.

ISSN:0003-6951    

DOI:10.1063/1.105047

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Using inverse photoemission, the uppermost minority spindband of Fe on GaAs(110) is found to move down by 0.9 eV for the first layer. This indicates a nearly complete collapse of the ferromagnetic exchange splitting at the interface. The decrease happens over a range of about 100 A˚, which parallels the reported decrease of the magnetization for epitaxial Fe films on GaAs

ISSN:0003-6951    

DOI:10.1063/1.105048

出版商:AIP    

年代:1991

数据来源: AIP