摘要:

A method is proposed for a thorough characterization of semiconductor substrates in terms of transport and recombination parameters. The method is based on exploiting the fundamentally simple geometry of a lateral bipolar transistor in low injection. Accurate two‐dimensional numerical solutions of the continuity equation show how the collector current depends on geometry elements and recombination parameters. In addition to the steady‐state analysis, the frequency dependence of the collector current was determined for a more direct assessment of the bulk and surface recombination. The theoretical results were experimentally demonstrated by measuring the surface recombination velocity and bulk lifetime in a silicon wafer.

ISSN:0021-8979    

DOI:10.1063/1.351663

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Low‐frequency (10–60 Hz) electrical noise has been measured for the first time in carbon fibers while they were subjected to tensile stress. The measurements were performed at room temperature. In all the fibers, a minimum in the noise was observed with applied stress. Low‐modulus ex‐PAN (polyacrylonitrile) fibers showed three times the increase in noise at the highest stress compared to the higher modulus fiber. Measurements were also made on vapor grown carbon fibers (VGCFs) both as‐grown and annealed. The highly graphitized VGCF showed the smallest increase in the noise with stress among the fibers studied. Our noise results can be related to the microstructure of the fibers. The fiber microstructure becomes better aligned with applied stress. Therefore, the noise would be expected to decrease. Our results, however, indicate that stress dependent noise in these fibers is caused by a combination of parameters such as fibril alignment and electronic characteristics.

ISSN:0021-8979    

DOI:10.1063/1.351664

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The interface trap density of statesDitof ultrathin SiO2film has been investigated as a function of process variables. The process parameters used were oxidation temperature (1000–1200 °C), oxide thickness (4–10 nm), and annealing condition, including ambient (deuterium, argon, and in vacuum), temperature (500 and 900 °C), and time (10–120 s). Analysis of as‐grown SiO2films showed that theDitdecreases with increasing oxidation temperature and/or oxide thickness. With annealing in argon or in vacuum at 900 °C, theDitdecreases exponentially at the initial stage, then starts to increase linearly with increasing time. Similar behavior was observed for 900 °C deuterium annealing. Deuterium annealing at 500 °C was more effective in the reduction of theDit, whereas argon annealing at the same temperature did not affect the density at all. A possible model for annealing kinetics is proposed to explain the experimental results.

ISSN:0021-8979    

DOI:10.1063/1.351665

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Room‐temperature electrotransmittance has been used in order to investigate the interband excitonic transitions in a 250‐A˚‐thick In0.53Ga0.47As/In0.52Al0.48As single‐quantum‐well system as a function of an externally applied electric field. Parity forbidden transitions, involving conduction‐band states with quantum numbers up ton=5, which become more pronounced at high electric fields were observed. The ground‐state and the forbidden transitions showed a significant red shift due to the quantum confined Stark effect. A comparison with previously reported results on thinner InGaAs/InAlAs quantum wells indicated that the wide‐well sample exhibits the largest shift, as expected from theory. Despite the appreciable Stark shift, the rather large, field‐induced linewidth broadening and the relatively low electric field at which the ground‐state exciton is ionized poses limitations on using this wide‐quantum‐well system for electro‐optic applications.

ISSN:0021-8979    

DOI:10.1063/1.351666

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A technique is developed for the design of input circuits of superconducting quantum interference devices (SQUIDs) including those based on high transition temperature (Tc) superconductors. A multitransformer SQUID circuit is reduced to a single‐loop one with effective values of its loop inductance and applied flux. A numerical model of a multitransformer magnetometer is formed and analyzed. The planar transformer coupling coefficient is evaluated. The multitransformer SQUID structures as a whole are optimized with respect to their performance, taking into account the limits set by fabrication technology. Three gradiometer‐type device designs are discussed. The most complex SQUID treated is a second‐order gradiometer for magnetoencephalography use which needs only a two superconducting films technology to be realized. Designs are based on available high‐Tcsuperconductor technology. Very competitive performance with high energy resolution and magnetic‐field gradient sensitivity is predicted at nitrogen temperature using a multitransformer coupling circuit.

ISSN:0021-8979    

DOI:10.1063/1.351667

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Within the framework of first‐order kinetics the activation energy spectrump(U) for thermal activated flux motion in YBa2Cu3O7−&dgr;single crystals is derived from the time decay of the magnetic polarization &mgr;0M(t). The distribution functionp(U) turns out to be temperature independent, so that the time dependence of &mgr;0M(t,T) can be described by one unique spectrump(U) in the whole temperature range 0 <T<Tc. Concerning the crystal directionsH∥cˆandH⊥cˆ, respectively, a threshold energy in the caseH⊥cˆis noticed which may be related to the Peierls potential, formed by the Cu‐O planes.

ISSN:0021-8979    

DOI:10.1063/1.351668

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The pressure wave propagation method is applied here to the study of charging and discharging processes of polymer films of spatial interest. The irradiation of the materials is performed by a monoenergetic electron beam in the range 5–50 keV. Since the irradiated surface of the sample is free, we extended the model of the induced signals, previously developed, to take into account the total reflection of the pressure at the polymer‐vacuum interface. All the experiments, irradiations and measurements, are operated in a vacuum environment. After the description of the experimental setup, typical signals showing the interfacial effects are discussed. They concern the behavior of the sample‐vacuum interface and charge injection at the target‐sample interface. These experiments, which were carried out both on metallized and nonmetallized samples bonded to the target electrode, allow a direct observation of charge injection at interfaces.

ISSN:0021-8979    

DOI:10.1063/1.351669

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Field ion emission from flat polar surfaces of ferroelectric crystals is predicted. Fast reorientation of the polar axis of such crystals may produce surface electrostatic fields of about 108V cm−1. The induced nonequilibrium charge may be screened by ion emission. The experimental conditions under which various kinds of ion emission may be observed are discussed.

ISSN:0021-8979    

DOI:10.1063/1.351670

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Raman scattering measurements on cubic boron nitride up to 1600 K are reported. The results indicate that at 1600 K the interatomic force constant is only ∼10% weaker than at room temperature and that cubic BN is therefore a good candidate for applications where high‐temperature mechanical strength is required. However, contrary to the behavior found for diamond, where the frequency changes with temperature were very nonlinear, it is found that in boron nitride both the TO and LO shift linearly with temperature at a rate of −0.036 cm−1/K.

ISSN:0021-8979    

DOI:10.1063/1.351671

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

An electroluminescent device was developed in which a single bipolar transport layer is used. High efficiencies can be obtained from this device by judiciously selecting a dopant that enhances the radiant recombination probability of carrier pairs and spaces this recombination zone away from the cathode.

ISSN:0021-8979    

DOI:10.1063/1.351672

出版商:AIP    

年代:1992

数据来源: AIP