摘要:

In this letter, we report the surface‐mode stimulated emission from optically pumped Ga0.11In0.89N at room temperature. The GaInN was deposited on the intermediate layer of GaN grown on the AlN buffer layer over sapphire substrate using horizontal metalorganic vapor phase epitaxy method. The peak wavelength and the full width at half‐maximum of surface‐mode stimulated emission was 406 nm and 25.6 meV, respectively, and the threshold of excitation power density was about 0.52 MW/cm2. ©1995 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.114778

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Highly conductingp‐type ZnSe and ZnSSe were fabricated by simple N2gas doping during molecular beam epitaxial growth without the use of any activation method, such as discharge and cracking.p‐type conduction in the N2‐gas doped ZnSe is produced by a shallow N acceptor state, which is obtained only when the dopant N2pressure is higher than 10−5Torr. When the N2pressure was varied from 3.2×10−5to 1×10−4Torr, the net acceptor concentration of N2‐gas doped ZnSe and ZnS0.06Se0.94films ranged from 3×1015to 2×1017cm−3and from 1×1016to 2.5×1017cm−3, respectively. Light emitting diodes with a N2‐gas dopedp‐cladding layer were fabricated and tested. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114779

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Ohmic contacts to heavily C‐doped AlGaAs were made using PdGeTiPt that had specific contact resistancesRc, as low as 1.7×10−6&OHgr; cm2when annealed at 600 °C. The less heavily doped samples annealed at temperatures between 350 and 500 °C were non‐Ohmic, andRcdecreased with increasing annealing temperature between 500 and 600 °C. For the more heavily doped samples,Rcdecreased with increasing annealing temperature.Rcincreased for all samples at annealing temperatures above 600 °C.Rcrose quickly by 102when the samples were reannealed at 300 °C for 20 h, but remained unchanged with further reannealing for up to 100 h. This behavior is consistent with partial compensation generated by the rapid out‐diffusion of Ga at low annealing temperatures and the subsequent in‐diffusion of Ge into the Ga vacancies left behind. The lowerRcobtained with the 600 °C anneal can be explained by an increased As out‐diffusion and the subsequent in‐diffusion of Ge into the As vacancies at the higher annealing temperatures. Interfacial reactions and elemental diffusion of the contacts investigated via transmission electron microscopy and elemental depth profiles obtained by Auger electron spectroscopy are also consistent with this mode. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114780

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Germanium surface segregation in Si/Ge/Si(100) heteroepitaxial structures has been studied by quantitative Auger electron spectroscopy (AES) and reflection high energy electron diffraction (RHEED). Ge segregation was measured for 1–4 ML Ge, for slow Si growth rates (3×10−4nm/s) at moderate deposition temperature (520 °C). A layer growth model is used to infer segregation probabilities between 90% and 98%, increasing with Ge layer thickness, especially between 1 and 2 ML. Using this model, the Ge profile in the cap layer is calculated. Surface roughness is just noticeable at 4 ML, and is incorporated into the model in an illustrative manner. A two‐state model is used to determine the segregation energy, 0.24±0.02 eV, for 2–3 ML. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114781

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We present structural and electronic data which indicate that the dominant defects in GaAs grown at low temperatures (LT GaAs) by molecular beam epitaxy (MBE) are As antisites (AsGa) and Ga vacancies (VGa), with negligible amounts of As interstitials (Asi). We show that the change of lattice parameter correlates with the concentration of AsGa, and that AsGaalone can account for the lattice expansion. We also show that the total concentration of AsGahas a characteristic second power dependence on the concentration of AsGain the positive charge state for the material grown at different temperatures. This can be understood provided thatVGadefects are the acceptors responsible for the carrier compensation. Our results are consistent with most experimental results and the theoretical expectation from the calculation of defect formation energies. We find that the conclusion may also be true in As‐rich bulk GaAs. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114782

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Experiments on a model of rapid single flux quantum (RSFQ) flip‐flop cell, based on high‐Tc(HTS) Josephson junctions show that it can operate as a voltage divider at frequency up to 400 GHz. The junctions were formed in YBaCuO film, deposited on novel Y–ZrO2bicrystals with two asymmetric 32° grain boundaries, about 10 &mgr;m apart, and allow a new design of RSFQ logic based on a single HTS layer. Small inductances (&bartil;10 pH) were made as narrow, submicron size slits. The junction widths were between 4 and 10 &mgr;m and for ten junctions located close to the tested circuits, the linear critical current densities atT=4.4 K were 10.7 &mgr;A/&mgr;m±50% for one grain boundary and 8.3 &mgr;A/&mgr;m±50% for the other one.IcRnwas about 1 mV±50%. A current density of half the expected value meant that the test circuit did not act as an ideal flip–flop down to the lowest frequency. As a voltage divider it gave a half value division up to 0.82 mV atT=4.4 K and to 0.4 mV at 30 K. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114783

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Photoresponse signals with widths as short as 1.5 ps are observed from epitaxial YBa2Cu3O7−&dgr; thin films using electro‐optic sampling techniques. Voltage transients less than 2 ps wide are seen in 100‐ and 200‐nm films exposed to 150‐fs laser pulses and cooled to 79 K. At low bias currents, the amplitude of the fast response varies linearly with the bias current, suggesting a kinetic inductive mechanism. A negative transient about 15‐ps long is also seen that may provide evidence for nonequilibrium recombination of excited quasiparticles into Cooper pairs. At high bias currents or large laser fluences, a fast tail with a decay time of about 10 ps appears in the response followed by a slow, resistive bolometric component due to sample heating. Nonequilibrium aspects of the photoresponse and the origin of the fast tail are discussed. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114784

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Distinctive microstructures of textured YBa2Cu3Ox(123) superconductors were examined by scanning electron microscopy and metallurgical microscopy. The samples were synthesized under a residual thermal gradient by using a modified melt textured growth on a Y2BaCuO5(211) substrate. Also, the unidirectional solidification by a zone‐melting method was performed to fabricate 123 superconducting bars up to 12 cm long placed on the 211 substrate in the horizontal arrangement, with a growth rateR=0.5 mm/h and a temperature gradient ofG=20 °C/cm (G/R=400 °C h/cm2). A ramping temperature of 1 °C/h (GR) was applied in both syntheses. Typical defects running parallel to (001) planes associated with 211 trapped particles were observed (so‐called platelet structure). Besides these, unusual defects were observed running parallel to (100) and (010) planes in textured 123+Pt superconductors, and interpreted as the result of an instability of the planar front in the presence of fine 211 particles. A theoretical model of planar interface stability confirms a strong dependence of stability region on the size of 211 particles in the melt. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114785

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The resistive transition in epitaxialc‐axis‐oriented HgBa2CaCu2O6+&dgr;(Hg‐1212) thin filmsTc∼122 K) in magnetic fields up to 9 T have been investigated. A considerably larger broadening of the resistive transition is observed for magnetic fields perpendicular to theabplane than for fields parallel to theabplane. Over the measured range of magnetic fields, the resistivity exponentially approaches zero as a function of decreasing temperature, suggesting a thermally activated flux creep behavior. The anisotropic characteristics of Hg‐1212 are compared with other high‐temperature cuprate superconductors and found to be less than for the Bi or Tl two‐layer systems, but still considerably larger than forYBa2Cu3O7−&dgr;. This can be qualitatively explained on the basis of the differences in the insulator spacing layer thickness between the adjacentCuO2layers in these cuprates. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114786

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Thick films of the high‐temperature superconductor Tl1Ba2Ca2Cu3Oywith high current densityJchave been deposited on polycrystalline Ag substrates by a spin‐coating method. The spin‐coated precursor films were annealed in a two‐zone Tl reaction furnace. Film thicknesses ranged from 10 to 30 &mgr;m, leading to good total current capabilities. The films have highly‐texturedc‐orientation as evidenced by rocking curves with FWHM of 4° for the (006) peak. Scanning electron micrographs revealed a dense, plate‐like layered structure and almost no reaction between the film and the Ag substrate. Values ofJc(77 K) up to 2.5×104A/cm2in zero field and more than 1000 A/cm2in a 1 tesla field (H∥caxis). ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114787

出版商:AIP    

年代:1995

数据来源: AIP