摘要:

The adsorption and dissociation ofH2Son GaAs(100) has been studied using high-resolution electron energy loss spectroscopy, thermal desorption spectroscopy, and isotope exchange techniques. The dissociative adsorption ofH2Sat 100 K produces only H–As species with a vibrational frequency of2072 cm−1.Upon warming to 200 K, the vibration of H–As clearly shifts to2105 cm−1,corresponding to a free H–As species. In addition, the formation of H–Ga(1887 cm−1) is also observed upon thermal annealing. In coadsorption studies ofH2Sand D atoms, three main desorption features ofH2Swere observed at 135, 200, and 375 K, respectively. The peaks at 135 and 375 K can be attributed to the desorption of molecularly adsorbedH2Sand the recombinative desorption of adsorbed H and HS, respectively. In addition to the 375 K peak, the desorption feature at 200 K also undergoes isotope exchange between coadsorbed D atoms andH2S.These observations strongly suggest that the dissociative adsorption ofH2Son GaAs(100) involves an intermediate of Ga–HS—H–As. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122559

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Capacitance–voltage characteristics were studied at various temperatures for Schottky barriers formed onn-GaAs/low-temperature-grown(LT)-GaAs/n-GaAssandwich structures. Charge accumulation at deep traps in the LT-GaAs layer was observed. At room temperature, theC–Vcharacteristics were found to be step-like with a wide plateau originated from emission of electrons accumulated in the LT-GaAs layer. At the temperature below 100 K, the electron emission from the LT-GaAs layer was completely suppressed. At intermediate temperatures (150–200 K), an effect of charge bistability was observed, which manifested itself as a hysteresis in the capacitance under sweeping the reverse dc bias. We suppose that the phenomenon takes place when the sweeping rate is higher than the electron emission rate but lower than the electron capture rate by the deep traps in the LT-GaAs layer. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122593

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The optical properties of lattice-matched GaAsSb/InGaAs/InP heterostructures with a varying InGaAs layer thickness (0–900 Å) were investigated. These structures display strong low temperature type II luminescence, the energy of which varies with the InGaAs layer thickness and ranges from 0.453 to 0.63 eV. The type II luminescence was used to determine directly and accurately the conduction band offset of these structures. The values obtained herein are 0.36 and 0.18 eV at 4.2 K for the GaAsSb/InGaAs and GaAsSb/InP heterojunctions, respectively, with the GaAsSb conduction band higher in energy. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122594

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Depth profiling measurements of photoluminescence on GaN epitaxial films grown onc-plane sapphire with metalorganic chemical vapor deposition have been performed. Dry etching technique of reactive ion etching is used with reactive gas ofCCl2F2/H2/Arunder an operation power of 200 W. Before and after each etching, reflectivity and photoluminescence spectra are measured. Film thickness is determined from both the scanning electron microscopy and the interference oscillations of the reflectivity spectra. An excellent steady etching rate of 19.2 nm/min is established. The photoluminescence measurements show that both the near-band-edge and the yellow luminescence remain fairly constant until the film thickness of about 700 nm, and a large drop is obtained in the ratio of near-band-edge to yellow emission intensity under about 300 nm. Analysis shows that the yellow luminescence emitters are mostly confined within the near interface region, and supports the origin of yellow luminescence to be due to native defects instead of impurities. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122595

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have investigated the atomic-scale morphology and composition of the GaSb-on-InAs heterojunction with cross-sectional scanning tunneling microscopy, and find a new “white-noise” component in the wave-vector-dependent roughness spectrum under epitaxial growth conditions routinely employed for type-II quantum well and interband cascade lasers. This phenomenon is associated with random substitutional defects at the interface whose concentration exceeds that due to bulk cross incorporation. We propose these defects originate from the thermodynamically favored but incomplete replacement of As by Sb at the InAs surface during anion exchange. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122596

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We discuss trends in residual stress as a function of film thickness, growth temperature, and substrate orientation for GaN/AlN/6H–SiC heterostructures. Films are mostly compressive for samples less than about 0.7 &mgr;m thick, are tensile up to about 2 &mgr;m, then abruptly become less tensile with stress values near 1 kbar thereafter. We interpret this as a successive relief of lattice mismatch and thermal stresses culminating in a catastrophic relief by unknown mechanisms at moderate thicknesses. These data indicate that relaxation processes in these heterostructures are not as well understood as previously supposed. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122597

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Results of photoluminescence (PL) study of the self-organized InGaAs/GaAs quantum dots (QDs) in a field-effect structure grown by metalorganic vapor phase epitaxy are presented. It has been found that the PL from the QDs strongly depends on the bias voltage. No PL from the QDs ground state can be observed from the reverse biased structure, whereas the PL signal recovers in the forward biased structure. It is proposed that the bias dependence of the PL signal results from the QDs electron occupancy changes driven by the electric field within the structure. Due to a long thermalization time, the photogenerated electrons are swept out of the QDs by the electric field before radiative recombination. The electrically modulated PL (e-m PL), making use of the bias dependence of PL signal, is proposed as a tool for QD investigation. The e-m PL spectra atT=300andT=4.2 Kare analyzed and discussed. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122598

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

In this letter, the noise performance of NbN-based phonon-cooled hot electron bolometric quasioptical mixers is investigated in the 0.55–1.1 THz frequency range. The best results of the double-sideband (DSB) noise temperature are: 500 K at 640 GHz, 600 K at 750 GHz, 850 K at 910 GHz, and 1250 K at 1.1 THz. The water vapor in the signal path causes significant contribution to the measured receiver noise temperature around 1.1 THz. The devices are made from 3-nm-thick NbN film on high-resistivity Si and integrated with a planar spiral antenna on the same substrate. The in-plane dimensions of the bolometer strip are typically 0.2×2 &mgr;m. The amount of local oscillator power absorbed in the bolometer is less than 100 nW. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122599

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A superconductor frequency divider based on rapid single flux quantum (RSFQ) logic has been demonstrated to operate from dc to 750 GHz with an error rate less than the measurement limit (25 MHz). This high operating frequency is made possible by the use of small (0.25 &mgr;m2), high critical current density Josephson junctions along with an optimized design having parameter margins of ±30&percent;. Simulations based on the Werthamer model are in reasonable agreement with the data and give a SFQ pulse width of 1 ps and a maximum power dissipation of 1.5 &mgr;W. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122600

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We reveal the intrinsic Josephson effect in aLa2−xSrxCuO4(LSCO) high-Tcsuperconductor. Nb counterelectrodes are deposited on top of mesas, which are formed on surfaces either parallel or perpendicular to theabplane of LSCO single crystals. Nb/LSCO interfaces behave as SNS Josephson junctions. For the junctions parallel to theabplane, we observe many branches in the current–voltage characteristics due to intrinsic Josephson effects. The voltage gaps between the branches are typically 0.1 mV, which is much smaller than the superconducting energy gap 2&Dgr;≅11 mV expected for LSCO from Bardeen–Cooper–Schrieffer theory. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122601

出版商:AIP    

年代:1998

数据来源: AIP