摘要:

Using reactive ion etching with CCl2F2/He a selectivity in etch rates between GaAs and AlGaAs of larger than 3000 has been obtained for low dc self‐bias voltages. Under isotropic etch conditions at low‐bias values this selectivity is used for the lateral etching of thin GaAs layers sandwiched between AlGaAs layers. The range of lateral etching is proportional to the square roots of the etch time and the thickness of the etched GaAs layer. Lateral etch widths of 4 &mgr;m for a GaAs layer thickness of 50 nm and larger than 20 &mgr;m for a thickness of 1 &mgr;m are achieved.

ISSN:0021-8979    

DOI:10.1063/1.351639

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We have successfully fabricated epitaxially grown YBa2Cu3O7/PrBa2Cu3O7(YBCO/PBCO) multilayer thin films on SrTiO3and LaAlO3substrates by dc/rf magnetron sputtering. The thicknesses of YBCO and PBCO varied from 1 to 8 unit cells. Satellite peaks in x‐ray diffraction patterns clearly indicate the formation of periodic modulation structures of different wavelengths. At a certain thickness of the YBCO layer, the zero resistance transition temperatureTc0decreased with the increase of the PBCO layer thickness. In contrast,Tc0increased with the increase of the YBCO layer thickness at a constant PBCO layer thickness.

ISSN:0021-8979    

DOI:10.1063/1.351640

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

SmCo5permanent magnets have been irradiated with 19.5 MeV protons at temperatures from about 300 to over 800 K. The results show that SmCo5magnets are very sensitive to irradiation at elevated temperatures. The relative magnetic flux loss has been calculated with a model based on the local heating caused by the incoming particle. The theoretical result agrees well with the experimental data.

ISSN:0021-8979    

DOI:10.1063/1.351641

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The dependence of the excitonic lifetime on the well width in InGaAs/InP (unstrained), InGaAs/GaAs, and InGaAsP/InP strained quantum well heterostructures is investigated by time‐resolved photoluminescence spectroscopy. We show that the main contribution to the lifetime variation comes from the change of the exciton binding energy. In the strained InGaAs/GaAs wells, the widest wells have a shorter lifetime than expected. We attribute this to the onset of plastic relaxation.

ISSN:0021-8979    

DOI:10.1063/1.351642

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The electronic structure of random sequences of superlattice layers is studied within the one‐dimensional Anderson model. We find significant variation of the degree of localization of the band‐tail states with the random stacking sequence. Comparison of the calculated results with existing data on the photoluminescence of disordered superlattices is made.

ISSN:0021-8979    

DOI:10.1063/1.351643

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Heteroepitaxy immediate to thermodynamical equilibrium is investigated for liquid phase epitaxy of Ge0.85Si0.15on Si(111). Below and beyond the critical thickness for strain relaxation, the GeSi layer grows in a two‐dimensional mode. The critical thickness agrees well with mechanical equilibrium considerations. Strain relaxation is found to take place by the confined formation of misfit dislocations directly at the Ge0.85Si0.15/Si interface. We do not observe half‐loop formation at the layer surface. The misfit dislocations (b=1/6⟨112⟩) form regular networks, which are buried under a structurally perfect relaxed GeSi layer virtually free of threading dislocations.

ISSN:0021-8979    

DOI:10.1063/1.351644

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

An attempt is made to study the magneto‐optical absorption for direct band parabolic semiconductors considering thek¯ dependence of the optical matrix element. Thus we have obtained the generalized expressions for the same coefficients which are consistent with the experimental results.

ISSN:0021-8979    

DOI:10.1063/1.351645

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Magnetic levitation and stiffness have been measured in several systems composed of a permanent magnet elastically suspended above a stationary melt‐textured sample of Y‐Ba‐Cu‐O. The levitation force and vertical stiffness have been calculated on the basis of magnetization measurements of the same system, and the calculated results showed excellent agreement with the experimental measurements. Based on the force and magnetization measurements, it is predicted that the same Y‐Ba‐Cu‐O material configured in a geometry suitable for magnetic bearings could produce a levitation pressure of 100–400 kPa at 20 K.

ISSN:0021-8979    

DOI:10.1063/1.351595

出版商:AIP    

年代:1992

数据来源: AIP