摘要:

A wet thermal oxidation method is proposed to passivate the electrochemically etched porous silicon. Bright and stable photoluminescence is achieved by wet oxidation at relatively low temperatures of 400–500 °C. The Fourier transform infrared absorption shows that the formation of SiH(O3), SiH(SiO2), SiH2(O2) bonds may be responsible to the stabilization of luminescence under the laser illumination. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361226

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Etch‐induced surface modifications, utilizing an electron cyclotron resonance source, have been studied as a function of controllable etch parameters. InGaP was etched with BCl3at a constant substrate temperature (100 °C) and bias voltage (−145 V) using microwave powers varying between 250 and 1000 W. The surface morphology, residual etch damage, and surface stoichiometry were strongly influenced by changes in ion flux. The etch‐induced lattice damage and surface smoothness increased as the ion energy was elevated. Low ion flux etching resulted in an In‐enriched P‐depleted surface suggesting nonuniform desorption of InClxwhich gave rise to the surface roughness observed at the low microwave powers. The smooth surfaces, achieved at the higher microwave power levels, were attributed to either efficient sputter‐assisted desorption of the InClxetch products or to InClxdesorption via plasma‐induced surface heating. Results of this study demonstrate that etching at microwave powers between 500 and 750 W induce low residual damage and smooth surfaces while maintaining a reasonable etch rate for device processing. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361227

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Deposition of thin diamond films on silicon (Si) substrates and in a reactor with fused silica walls can lead to the incorporation of Si impurities. In the present work, impurities in the bulk of the films were analyzed quantitatively using complementary diagnostic techniques (elastic recoil detection, electron microprobe analysis and secondary ion mass spectrometry), while surface analysis was achieved with x‐ray photoelectron spectroscopy. The Si contamination level in the bulk reaches up to 0.16 at. %. We show that the presence of Si impurities correlates with the fluorescence background that accompanies the 1332 cm−1diamond peak in the Raman spectra. Experiments were performed to distinguish between the Si originating from the wall and from the Si substrate. The effect of O2added to the process gases is also investigated. The diamond films were prepared in a recently developed plasma reactor using a novel configuration of surface‐wave‐sustained discharge: the reactor operation is akin to that of the well‐known plasma‐ball systems. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361228

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The electroluminescence and photoluminescence light‐emitting devices based on poly(p‐phenylene vinylene) (PPV), with emitting layers of different thicknesses, were examined. It was shown that microcavity effects occur in thin PPV single‐layer sandwich structures (ITO/PPV/Al, Au/PPV/Al) in both electroluminescent and photoluminescent emission. Microcavity effects were demonstrated for a range of different PPV layer thicknesses down to 40 nm. We have successfully prepared resonant‐cavity single‐layer light‐emitting diodes with enhanced external quantum efficiencies of up to 0.1% photons/electron, with aluminum as the electron injecting and gold as the hole injecting electrode. Less pronounced microcavity effects were observed on devices with ITO as the hole injecting contact, due to the low reflectivity of the ITO‐glass interface. These findings were confirmed by theoretical simulations based on an optical transfer matrix formalism. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361229

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We describe a 9 &mgr;m AlGaAs/GaAs asymmetric quantum well infrared photodetector with voltage tunable spectral bandwidth. A very narrow spectral response of 9.2 meV (0.6 &mgr;m) full width half maximum is observed for an applied electric field of 28 kV/cm. The linewidth quadruples when the bias polarity is reversed, with very little shift in the peak detection wavelength. This structure is based on a conventional intersubband photodetector modified by using AlGaAs barriers that are graded in Al content and by adding a thin AlGaAs confinement layer on one side of the well. The asymmetry in the barriers is shown to give rise to the dependence of the spectral linewidth on applied bias. As well, a series of unusually well‐resolved and intense bound‐to‐continuum transitions are observed at low bias, that may indicate that the unique barrier shape also leads to enhanced electron interference effects at the well/barrier interfaces.

ISSN:0021-8979    

DOI:10.1063/1.361230

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We study picosecond carrier transport dynamics induced by 200 fs 1.55 &mgr;m optical pulses in charge injection transistor structures. We propose and demonstrate a new optoelectronic method for exploring the interactions of hot majority carriers and cold minority carriers, as well as the optical control of real space transfer in these devices. The minority holes photogenerated in the channel produce substantial cooling of the hot‐electron majority carriers and lead to the reduction of the real space transfer. The new method also provides a direct measure of the minority carrier lifetime in the transistor channel. These effects are demonstrated in InGaAs‐channel devices with both InAlAs and InP barriers. The similarities in the device characteristics are explained in terms of the interaction of photogenerated minority holes with majority electrons in the channel leading to a photoconductor‐like drain current and to a reduction in the real space transfer collector current. The differences are attributed to the different conduction and valence band energy offsets between the wide band gap barrier and the low band gap collector and channel layers. Furthermore, the InAlAs‐barrier device shows a capability of serving as a practical photodetector with the measured, system‐limited recovery speed of ∼5 ps. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361231

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We consider a model system consisting of an infinitely long magnetic dipole line placed symmetrically above an infinitely long superconducting strip. Using the Meissner effect of superconductors, we derive analytical expressions of the levitation forces acting on the dipole line. At lowest‐order approximation, we discuss the possible application of our model system to estimate the upper limit of the levitation forces in some magnetic bearing systems. In one example, the model correctly calculated the vertical vibration frequency of an experimental superconducting bearing.

ISSN:0021-8979    

DOI:10.1063/1.361232

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Thick piezoelectric lead zirconate titanate (PZT) films (ceramic–ceramic 0–3 composite films), using a new sol‐gel based process, have been produced and used to coaxially coat optical fibers. Coated PZT of up to 200 &mgr;m thick and 10 cm long have been achieved. Using thick PZT coated single mode optical fibers, in‐line phase modulators are designed, built and tested. Theoretical and experimental investigations of such phase modulators are also presented. The measured phase modulation ranges from hundreds of kilohertz to several megahertz. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362661

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A new model for the low frequency (LF) noise in the base current of polysilicon emitter bipolar junction transistors (BJTs) is proposed. This model is based on the carrier number fluctuation approach and satisfactorily accounts for the base current noise characteristics. The base current fluctuations are ascribed to surface and volume noise sources. The surface noise arises from the low frequency fluctuations of the surface generation–recombination base current component due to the dynamic trapping–detrapping of carriers into/from slow states located in the spacer oxide at the periphery of the emitter/base junction. The volume noise results from the intrinsic fluctuations of the diffusion base current due to the carrier number fluctuations in the emitter or at the emitter–base junction. This LF noise model has been applied to BJTs subjected to hot carrier stress after reverse biasing of the base–emitter junction. The evolution of the base current noise characteristics after stress clearly demonstrates that the hot carrier injection leads to a substantial increase of the surface base current noise component whereas the volume noise component as well as the collector current noise is nearly insensitive to the degradation‐induced defects. The application of the model provides an evaluation of the slow and fast trap densities generated as a function of the stress level. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361233

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Epitaxial thin films of Y‐doped SrZrO3have been grown on MgO(001) by pulsed laser deposition. The deposition process has been performed at temperatures of 1000–1200 °C and at an oxygen pressure of 1.5×10−1mbar. The samples are characterized by Rutherford backscattering spectrometry/channeling (RBS/C) and x‐ray diffraction (XRD). We found an epitaxial relationship of SrZrO3(0k0) [101]∥MgO (001) [100]. Good crystalline quality is confirmed by RBS/C minimum yield values of 9% and a FWHM of 0.35° of the XRD rocking curve. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361234

出版商:AIP    

年代:1996

数据来源: AIP