摘要:

The subband electronic structure of Si&dgr;-doped GaAs grown by metal organic vapor phase epitaxy was investigated using magnetotransport measurements. The work focused on the effect of illumination. We found that illumination leads to a slight increase of the quasi-two dimensional electron gas density in the well. This increase does not depend on the illumination intensity. The illumination-generated electron density weakly increases with an increase in the Si&dgr;-doping concentration. We also experimentally confirmed that illumination only slightly alters the electron densities of the occupied subbands and the illumination-generated electrons populate one previously empty subband. Only a fraction of the illumination-generated electrons persist but the newly occupied subband under illumination remains populated in the dark after removal of the illumination. The experimental results suggest that the DX centers are unlikely to be populated in our Si&dgr;-doped GaAs regardless of the doping concentration. The weak and partially persistent photoconductivity effect observed in Si&dgr;-doped GaAs may arise from ionization of other Si localized states.©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119317

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report a double-slit experiment of hot electrons in a semiconductor under a magnetic field. The pitch of the double slit buried in the semiconductor is 40 nm and the electron energy is of the order of 100 meV. By applying a magnetic field, the change in current that passes through the slits is observed at the segmented collector. The measured current shows a clear minimum aroundB=0 T, with this behavior agreeing with a theoretical calculation based on double-slit interference. Quantitative estimation is consistent with this order of current variation. We think that these results show evidence of the observation of hot electron interference by a double slit in a semiconductor. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119318

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

High quality 15-period strain-compensated InAsP/InGaP electroabsorption (EA) modulator structures have been grown by atmospheric pressure metal–organic vapor epitaxy. The incorporation of large compressive strain (∼1.7&percent;) in the InAsP wells and tensile strain (∼−1.8&percent;) in the InGaP barriers necessitated the growth of a few InP monolayers between the wells and barriers. The high structural quality of such samples has been demonstrated by (cross-sectional transmission electron microscopy analysis to be free of misfit dislocations and thickness undulations. The detection of a sharp and abrupt room-temperature exciton peak both in the photoconductivity and photoluminescence measurements further confirmed their excellent optical quality. 100 &mgr;m cavity length EA modulators fabricated in these structures exhibited excellent performances namely, an extinction ratio higher than 20 dB for 2.5 V drive voltage, a 3 dB bandwidth over 20 GHz, and low coupling losses to fiber (less than 2.5 dB per facet). ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119319

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A low resistance Pd/Sb/Zn/Pd Ohmic contact based on the solid phase regrowth principle has been investigated top-InP. Contact resistivity as low as∼2×10−6 &OHgr; cm2has been obtained for samples annealed at 500 °C for 1 min. The Ohmic behavior can be rationalized by the formation of a heavily doped surface layer or a heterojunction. The InSb phase responsible for the observed low resistivity is identified using the x-ray diffraction technique. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119320

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Indirect &Ggr;-L scattering within the well, and real space carrier transfer to the barrierX1cstates are shown to significantly affect the carrier dynamics inIn0.48Ga0.52P/In0.5Al0.5Pmultiple quantum wells. When carriers transfer to the indirect states occurs, the carrier dynamics is modified by the slow return of the carriers from the low mobility states to the well. As a result, the absorption recovery time increases by almost an order of magnitude. Carrier transfer to the indirect states also increases the carrier lifetime to values characteristic of indirect recombination. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119275

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The resonant tunneling of electrons through a 20 nm scale InAs quantum dot bound by a pair of very thin AlAs barriers is studied. A well-resolved composite peak resulting from the ground1sstates was observed at 4.2 K in current–voltage characteristics. By investigating the effects of inplane magnetic fields, the shape of the wave function and the spatial extent of the first two electronic states are clarified. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119276

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new metallization scheme has been developed to form Ohmic contacts ton-GaN. Contacts were fabricated by sputtering the intermetallic compound,PtIn2on metal–organic vapor phase epitaxy grownn-GaN(n∼5×1017 cm−3)with some of the contacts subjected to rapid thermal annealing. Contacts in the as-deposited state exhibited nearly Ohmic behavior with a specific contact resistance of1.2×10−2 &OHgr; cm2. Contacts subjected to rapid thermal annealing at 800 °C for 1 min exhibited linear current–voltage characteristics and had specific contact resistances less than1×10−3 &OHgr; cm2. Auger depth profiling and glancing angle x-ray diffraction were used to examine the interfacial reactions of thePtIn2/n-GaNcontacts. Consistent with estimated phase diagram information, the results from Auger depth profiling and glancing angle x-ray diffraction indicated the formation of(InxGa1−x)Nat the contact interface, which could be responsible for the Ohmic behavior ofPtIn2contacts. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119277

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present an electrostatic model to determine the surface charge density and confinement potential in etched AlGaAs/GaAs quantum wires. In far-infrared transmission experiments we have determined the resonance frequencies of the dynamic eigenmodes of the quantum wire, which gives an independent determination of the confinement potential. We find good agreement with the modeled potential, which shows that this model gives a very good description of the electronic system. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119278

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report on progress in the development of high current density NbN/AlN/NbN tunnel junctions for applications as submillimeter wave superconductor-insulator-superconductor mixers. A very high current density up to 54kA/cm2, roughly an order of magnitude larger than any reported results for all-NbN tunnel junctions, was achieved in the junctions with about 1 nm thick AlN barriers. The magnetic field and temperature dependence of critical supercurrents were measured to investigate the Josephson tunneling behavior of critical supercurrents in the high-Jcjunctions. The junctions showed high-quality junction characteristics with a large gap voltage of 5 mV and sharp quasiparticle current rise (&Dgr;Vg=0.1mV). TheRsg/RNratio was about 5 with aVmvalue of 14 mV measured at 4.2 K. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119279

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Bulk melt texturedYBa2Cu3O7−&dgr;samples with single grains of about 24 mm diameter were obtained by use ofSmBa2Cu3O7−xseed crystals. The maximum trapped fieldB0in the gap between two samples was investigated as function of temperature.B0increased from 1 T at 77 K to 8.5 T at 51.5 K, which is the highest trapped field achieved in nonirradiated samples. At low temperatures, cracking of the samples was observed under magnetic pressure. In this temperature range, the trapped field is limited by the mechanical strength of the samples, for which a value of 25 MPa was estimated. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119280

出版商:AIP    

年代:1997

数据来源: AIP