摘要:

It is shown that a nonlinear lumped‐circuit transmission line with a bandpass can transmit weak signals and reflect strong signals. Such nonlinear bandpass filters have an absolute limit on the power passed and may prove useful as circuit protectors.

ISSN:0021-8979    

DOI:10.1063/1.344949

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A comprehensive analysis of pulse formation in inductive‐energy pulsed power circuits is presented. The output waveforms, with relevant circuit parameters, are derived for four basic systems, including two new circuit configurations useful for practical applications.

ISSN:0021-8979    

DOI:10.1063/1.344950

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Power loss mechanisms in illuminated and nonilluminated photovoltaic cells are investigated by an ac calorimetric method. In this electrothermal (ET) method, periodic temperature changes, caused by periodic electrical excitation, are sensed as a function of external parameters, e.g., applied voltage. ET signals on crystalline silicon and thin‐film CuInSe2/CdS solar cells are measured as a function of applied voltage. The results are compared to those obtained from an energy balance model. Inherent to the model is the occurrence of injected carrier cooling. The ability of ET measurements to separate different power loss mechanisms is discussed and compared to that of conventional photothermal ones (e.g., photoacoustic).

ISSN:0021-8979    

DOI:10.1063/1.344951

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Epitaxial regrowth is emerging as an important step in the processing and realization of optoelectronic integrated circuits. We have studied the dc and microwave characteristics of regrown In0.53Ga0.47As/In0.52Al0.48As modulation‐doped field effect transistors on InP substrates and have compared these with the characteristics of normally grown devices. The low‐field transport properties of the heterostructures are degraded due to the increased interface roughness caused by processing and regrowth. The dc and microwave characteristics in terms ofgm(399 mS/mm),fT(20 GHz), andfmax(35 GHz) are slightly degraded in the regrown devices compared to the normally grown ones. The density of states at the active heterointerface is not appreciably increased compared to normally grown devices. The low‐frequency 1/fnoise level is higher in the saturation regime in the regrown devices. Our results indicate that there may be increased density of trapping centers in the regrown In0.52Al0.48As buffer layer below the active channel.

ISSN:0021-8979    

DOI:10.1063/1.344952

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

An analytical design method of self‐shielded planar coils is proposed using the three‐dimensional Fourier expansion of the magnetic field generated by planer currents. A numerical example is given for a simple current hoop as a primary coil, and the magnetic fields outside the self‐shielded coil structure are calculated, showing good shield performance.

ISSN:0021-8979    

DOI:10.1063/1.344953

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

This paper reports experimental results on the longitudinal piezoresistive effect ofn‐type metal‐oxide‐semiconductor field‐effect transistors (MOSFETs) with the particular aim of obtaining data appropriate for the computer simulation of silicon sensors. The measurements were performed on MOSFETs of different geometries including short channel devices with a channel length of 2 &mgr;m. The MOSFETs were integrated on (100)‐oriented silicon with current flow parallel to the crystallographic ⟨110⟩ direction. The influence of the piezoresistive effect on the total output characteristic of these devices was studied. The corresponding first‐ and second‐order piezoresistive coefficients were determined in the linear regime of the output characteristic as a function of the transistor geometry as well as of the gate voltage.

ISSN:0021-8979    

DOI:10.1063/1.344954

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Levitation forces between a small permanent magnet and a disk of bulk high‐temperature superconductor at 77 K were measured as a function of vertical separation for disks of composition Y‐Ba‐Cu‐O, Ag/Y‐Ba‐Cu‐O, (Pb,Bi)‐Sr‐Ca‐Cu‐O, and Tl‐Ba‐Ca‐Cu‐O. The forces were highly hysteretic; however, for all samples, on the initial descent of the magnet toward the disk, the force was unique, independent of magnet speed, and varied approximately as the negative exponential of the separation distance. Magnetic stiffness, associated with minor hysteresis loops, was found to be approximately proportional to the levitation force, and nearly independent of magnet configuration and superconductor composition.

ISSN:0021-8979    

DOI:10.1063/1.344927

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Intersubband absorption in GaAs/AlGaAs multiple quantum wells (MQW) is measured using a novel integrated detector‐waveguide structure. The responsivity spectra of MQW infrared photodetectors is demonstrated to follow exactly the intersubband absorption spectra at various temperatures and bias. The blue shift of the bound‐to‐continuum state intersubband absorption peak with lowering of temperature is observed to track the change of the conduction‐band offset. The absorption peak showed only a slight Stark shift since the field in the wells is small in these narrow‐well/thick‐barrier structures and partly screened by the high doping.

ISSN:0021-8979    

DOI:10.1063/1.346075

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

This communication presents a comparative study of polish‐induced effects in ⟨100⟩ GaAs by Raman spectroscopy (strain) and cross‐sectional transmission electron microscopy (dislocation density). It is found that the depth and polish‐time dependence of both the strain and dislocation density obey the same relationship. However, the skin depth evaluated by Raman scattering is a factor of 10 smaller than that determined from transmission electron microscopy.

ISSN:0021-8979    

DOI:10.1063/1.344928

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Y‐Ba‐Cu‐O superconducting thin films on 100 and 110 SrTiO3were deposited under identical conditions by annealing thick layers of sequentiallye‐beam evaporated Cu, Y, and BaF2. A comparison of these films is presented. Using a variation on the same technique, a 135‐&mgr;m‐wide superconducting strip was deposited on 100 SrTiO3by patterning of the first layer (copper) in the multilayer stack. Resistance data for this sample are presented. Superconducting dipoles (50 ×850 &mgr;m) were also patterned on yttria‐stabilized ZrO2by this same technique.

ISSN:0021-8979    

DOI:10.1063/1.344929

出版商:AIP    

年代:1990

数据来源: AIP