摘要:

This paper studies the effects of gate voltage on heat generation and transport in a metal–semiconductor field effect transistor made of gallium arsenide (GaAs) with a gate length of 0.2 &mgr;m. Based on the interactions between electrons, optical phonons, and acoustic phonons in GaAs, a self‐consistent model consisting of hydrodynamic equations for electrons and phonons is developed. Concurrent study of the electrical and thermal behavior of the device shows that under a source‐to‐drain bias at 3 V and zero gate bias, the maximum electron temperature rise in this device is higher than 1000 K whereas the lattice temperature rise is of the order of 10 K, thereby exhibiting nonequilibrium characteristics. As the gate voltage is decreased from 0 to −2 V the maximum electron temperature increases due to generation of higher electric fields whereas the maximum lattice temperature reduces due to lower power dissipation. The nonequilibrium hot‐electron effect can reduce the drain current by 15% and must be included in the analysis. More importantly, it is found that the electron temperature rise is nearly independent of the thermal package conductance whereas the lattice temperature rise depends strongly on it. In addition, an increase of lattice temperature by 100 K can reduce the drain current by 25%. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359082

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Switchable polarization can be suppressed in Pb(Zr,Ti)O3thin films by optical, thermal, electrical, and reducing processes. The optical suppression effect occurs by biasing the ferroelectric near the switching threshold and illuminating the material with band gap light; the thermal suppression effect occurs by biasing the ferroelectric near the switching threshold and heating the material to ≊100 °C. The electrically induced suppression effect, known as electrical fatigue, occurs by subjecting the ferroelectric capacitor to repeated polarization reversals. We find that the suppressed polarization in these three cases can be restored to essentially its initial polarization value by creating electronic charge carriers in the ferroelectric. This strongly suggests that all three forms of degradation largely involve locking domains by electronic charge trapping at domain boundaries. The fourth form of polarization suppression, a reducing treatment, was obtained by annealing the crystallized PZT films at 400 °C in nitrogen. The suppressed polarization could not be restored by injecting electronic charge into the reduced films, indicating that the mechanism for polarization suppression is different. In this case, it appears as though ionic defects, such as oxygen vacancies, are responsible for locking the domains, and hence, suppressing the polarization. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359083

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Low‐noise dc superconducting quantum interference devices (SQUIDs) were fabricated by thin film deposition of Bi2Sr2Ca Cu2O8+x(BSCCO) on bicrystalline substrates of SrTiO3with misorientation angles &THgr; from 24° to 45°. An optimized dc SQUID design (&bgr;L=1) was developed for &THgr;=24°. Therein the SQUID inductance was varied between 7 and 80 pH. Fabricated dc SQUIDs operated at 77 K as well as high‐quality YBa2Cu3O7−y(YBCO) SQUIDs, especially the 1/f and white noise levels were in the lowest range of data reported so far for YBCO SQUIDs and are two orders of magnitude better than noise data published this far for BSCCO SQUIDs at 77 K. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359084

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We observe electrically asymmetrical source‐drain characteristics in in‐plane‐gated transistors with shaped channels, and investigate them for different geometries. We give a qualitative explanation of the asymmetry, which is supported by voltage contrast scanning electron micrographs and the measured interaction between two neighboring channels. These shaped channels show a much higher dc voltage gain than conventional in‐plane‐gated transistors. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359085

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

During the process of pulsed laser deposition of thin film materials, the impingement of the laser ablated particles onto the substrate increases the substrate temperature. In this work, the energy exchange between the ablated particles and the substrate is analyzed. The substrate temperature rise is studied via a transient two dimensional heat transfer model. In particular, the temperature evolution of silicon and quartz substrates induced by the deposition of carbon and copper films are examined. The effects of experimental conditions on the maximum substrate temperature rise are discussed. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359086

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The magnetic properties of ∼2500‐A˚‐thick Co films evaporated in various oxygen pressures have been studied. Our results show that as the saturation magnetization is reduced, the coercive force in the perpendicular direction (Hc⊥) increases to a maximum (1.6 kOe); this change is consistent with results of previous investigations. The sign of the effective perpendicular anisotropy field (Hk eff=2K/Ms−4&pgr;Ms), as determined by ferromagnetic resonance (FMR), is always negative (<−4 kOe), indicating that the anisotropy field (2K/Ms) does not overcome the demagnetizing field (4&pgr;Ms). Our FMR results also confirm that films having anHc⊥value larger than that in‐plane coercive force (Hc∥ ) do not always demonstrate a value ofHk eff≳0. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359087

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Infrared absorption spectra of molecular beam epitaxial grown GaInAsSb alloys, GaInAsSbp‐i‐nandp‐nphotodiode structures are reported. It is found that the absorption edge of theN‐type GaInAsSb has a blue shift compared with that of the unintentionally doped GaInAsSb, which is thought to be the Moss–Burstein shift. On the other hand, the absorption edges of thep‐i‐nandp‐nphotodiode structures have red shifts compared to the respective layers, which results from the built‐in field induced Franz–Keldysh effect. By using the WKB method, we have calculated the absorption spectra for photons of energy less than the energy gap. The theoretically predicted red shift is in good agreement with the experimental results. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.359088

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The measurements of internal photoemission and photovoltage within the temperature range of 7–300 K have been performed for unannealed and annealed Au/n‐Si and Au/n‐GaAs samples. From the internal photoemission measurements, it was observed that annealing at different temperatures does not affect the relativity of interfacial Fermi‐level pinning to either the conduction band (for Au/GaAs) or the valence band (for Au/Si) but leads to a significant change of the Schottky barrier height. On the other hand, the photovoltage measurements show that the current transport at the metal/semiconductor interfaces is seriously affected by annealing. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359089

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Room‐temperature photoreflectance (PR) and photoluminescence (PL) spectra in heavilyn‐doped GaAs were compared. It was found that for highly degenerate semiconductors the critical energy measured by the PR equals to the peak energy of the PL spectrum. When Fermi level lies below the conduction‐band minimum, the PR spectra revealed the band‐gap energy as well as the energyEmaxat which the electron concentration per unit energy in the donor band becomes maximum, and this maximum was observed to merge in the conduction‐band at about 3×1017cm−3electron concentration. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359090

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

X‐ray diffraction was performedinsituduring annealing of a Co/Ti/Si(001) multilayer, which produced an epitaxial CoSi2layer. The results indicate that the Ti layer did not stay intact during the reaction, and thus could not act like a membrane, moderating Co/Si interdiffusion. Strongly textured phases (M) formed prior to CoSi2nucleation, and was unobservable upon completion of the anneal. Nucleation and growth of CoSi2on Si(001) took place in the presence ofM, new Co‐Ti‐(O) phases that were located at the metal/Si interface, and thusMmight play an important role in the perfection of the silicide. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359091

出版商:AIP    

年代:1995

数据来源: AIP