摘要:

A metastable SiGe-on-insulator structure is realized by a high-dose74Ge+ion implantation in the overlayer of silicon-on-insulator followed by solid phase epitaxial regrowth. Studies of the optical properties of the germanium-implanted and post-implantation annealed layers with 18&percent; peak germanium concentration were carried out using photoluminescence (PL) spectroscopy. The electrical integrity of the strained layer was qualitatively inferred from the pseudo-mosfet characterization technique. The PL results show that the broadband (BB) emission related to germanium implantation damage can be completely eliminated by post-implantation thermal treatment. PL spectra and measured transconductance of the sample heat-treated at 500 °C indicate conclusively that a defect-free strained SiGe layer has been formed. However, samples heat-treated at higher temperatures show degradation in the charge carrier lifetime, a new BB emission with 0.816 eV peak energy and an emergence of defect related emission at 0.870 eV for samples annealed at and above 900 °C. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121536

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Iron doping of InP andGaInAsP(&lgr;g=1.05 &mgr;m)layers grown by metalorganic molecular beam epitaxy was studied using elemental source material in combination with a conventional effusion cell. This study was aimed at the creation of semi-insulating optical waveguides under growth conditions compatible with selective area growth. Secondary ion mass spectroscopy measurements revealed a reproducible and homogeneous incorporation behavior of the iron dopant in the materials investigated. Resistivities in excess of109 &OHgr; cmwere obtained for both compositions at medium doping levels. GaInAsP/InP waveguide structures grown at485 °C—the minimum temperature necessary for selective deposition—exhibited averaged resistivities of5×107 &OHgr; cmin combination with optical losses of2.5±0.5 dB/cm.©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121537

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report on the results of the measurements of the low-frequency nitride/gallium aluminum nitride (GaN/GaAlN) heterojunctions grown on sapphire substrates. The noise spectra have the form of the1/fnoise with the Hooge parameter of approximately10−2.The effects of band-to-band and impurity illumination on the low-frequency noise show that the nature of the1/fnoise in GaN might be a result of the occupancy fluctuations of the tail states near the band edges. This mechanism of the1/fnoise is similar to that in GaAs and Si. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121538

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Small amounts of As residual pressure were found to affect the structure of cubic GaN growing surfaces in molecular beam epitaxy growth, i.e., modification of surface reconstruction structures, stabilization of reconstructed flat surfaces at high substrate temperatures, and preferential growth of the cubic phase. These As surfactant effects are discussed in relation to the atomic arrangement of the As-passivated surface of GaN. It was shown that the quality of cubic GaN epilayers can be improved by utilizing a small amount of As residual pressure. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121539

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have examined levitation forces of field cooled (2.3 T) and zero field cooledYBa2Cu3O7−&dgr;superconductors opposed by a SmCo magnet. We have achieved unusually large levitation forces (140 N) and pressures(44.6 N/cm2)in field cooled measurements. 5–10 subsequent cycles, of approach and retreat of the magnet, result in a 10–20&percent; decrease in force, which then stabilizes. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121540

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Fabrication of all-refractoryNb/Al–AlOx–Tisuperconducting tunnel junctions using selective titanium etching process (STEP) is described. Results including anodization properties of Ti, and junction’sI–Vcharacteristics and subgap currents measured in the temperature range of 0.4–9.2 K are presented. The junctions show fairly high quality with respect to their stability and reproducibility. Possible utilization of these junctions as superconductor–insulator–normal metal type devices operating around 100 mK and above for ultrasensitive microbolometer and electronic microrefrigerator applications is discussed. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121541

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report on the growth of superconducting Nb-dopedSrTiO3thin films onLaAlO3substrates by pulsed laser deposition. We find optimum Nb doping and high mobility for growth near 870 °C and chamber pressures below3×10−4Pa (2×10−6Torr). The transport properties were measured from 300 K to 150 mK. The most highly doped samples display metallic behavior, and are superconducting below 350 mK, with transition temperatures similar to those of bulk single crystals. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121542

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Directly coupled dc superconducting quantum interference device (SQUID) magnetometers onLaAlO3substrates were fabricated using ramp-edge superconductor/normal-metal/superconductor junctions, where Ag-dopedYBa2Cu3O7−xwas used for the electrode andPrBa2Cu3O7−xfor the normal-metal barrier. A flux noise of8×10−6 &Fgr;0 Hz−1/2at 10 kHz measured with a dc bias current was achieved at 75 K, which corresponded to a field sensitivity of400 fTHz−1/2for a magnetometer with a pick-up loop area of8.5 mm×7.5 mm.Most significantly, the noise floor increased at lower frequencies with a frequency dependence slightly less than1/f.The field noise of the SQUID magnetometers increased by only 25&percent; after cycling the devices from zero field to 500 mG. In a static earth’s magnetic field background, the field noise of the SQUID magnetometers increased by less than a factor of 2. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121543

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have fabricated a nanometer-scale transistor that operates by using a gate field to modulate the transmission of electrons through a lateral metal/oxide tunnel barrier. Our initial devices have a 30-nm-wide lateralNb/NbOxtunnel junction on top of a planarAl2O3/Alburied gate. We observe effective modulation of the source–drain current with gate bias at room temperature with negligible gate leakage current. We identify the materials issues that currently limit the device performance, and we offer direction for future device improvements.

ISSN:0003-6951    

DOI:10.1063/1.121544

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We obtain femtosecond (200 fs) time resolution using a scanning tunneling microscope on surface plasmon polaritons (SPPs) generated by two 100 fs laser beams in total internal reflection geometry. The tunneling gap dependence of the signal clearly indicates the tunneling origin of the signal and suggests that nanometer spatial resolution can be obtained together with femtosecond temporal resolution. This fast response, in contrast to the picosecond decay time of SPPs revealed by differential reflectivity measurements, can be attributed to a coherent superposition of SPPs rectified at the tunneling junction. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121545

出版商:AIP    

年代:1998

数据来源: AIP