摘要:

We present a mean‐field model for the mixed state of superconducting microbridges with low pinning forces which accounts for theI–Vcharacteristics measured on superconducting flux flow transistors (SFFTs) as well as the improvement of the performances of these devices when they include several microbridges. From the model it turns out that the vortex motion is not mostly driven by the bias current as is assumed in classical flux flow descriptions but by a diffusion process. Moreover, it is shown that due to the magnetic coupling between bridges, the critical current of a device withnbridges is larger thanntimes the critical current of a single bridge. Expressions for this increase in the critical current and the current gain of these devices are given. The model also accounts for the dynamic resistance modulation of SFFTs when an external magnetic field is applied. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360385

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The degradation and annealing properties of 1 MeV electron‐irradiatedn+pdiffused junction InP solar cells are reported in detail. The solar cells were characterized through current–voltage measurements under simulated solar illumination at 1 sun, AM0. The radiation‐induced defect spectra were characterized through deep level transient spectroscopy. At fluences up to 1015cm−2, cell degradation was primarily due to a decrease in the short‐circuit currentIscwhich occurred during the introduction of the hole trap, H4. Most of this degradation could be removed by minority‐carrier injection annealing of the H4 defect at temperatures as low as 225 K. At higher irradiation fluences, up to 1016cm−2, cell degradation was dominated by a decrease in both the open‐circuit voltageVocand the fill factor. This degradation was caused by a large radiation‐induced recombination current and by carrier removal which was associated with the introduction of the hole trap H5 and the electron traps EA, EC, and ED. Most of the effects of the recombination current and some of the carrier removal were removed by concurrent injection and thermal annealing between 373 and 400 K where the residual H4 defect concentration and the H5 defect were removed. Essentially full cell recovery was achieved after subsequent annealing between 450 and 500 K where the electron traps also showed a partial annealing stage. Thermal annealing without illumination in the range of 350–500 K showed the same defect annealing stages suggesting that the cell recovery in this temperature range is due solely to thermal annealing. The data are summarized to give a model for the radiation‐induced degradation and annealing of these InP solar cells. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360386

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Simultaneous near field scanning optical and atomic force microscopy with a microfabricated photocantilever reveal both optical and topographical distributions. The cantilever tip changes the evanescent field into scattering light, and this scattering light is detected with a photodiode fabricated in the tip of the cantilever. The cantilever deflection signal leads to atomic force images. The resolution for imaging the evanescent field variation was 20 nm (&lgr;/30). The near field optical and atomic force images indicate that the same point of the cantilever tip generates both optical and atomic force signals. This method is a new approach to optical and topographical microscopy with nanometer resolution. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360387

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We present a physical model to study the interface states in p‐n heterostructures at different ambient temperatures. Field‐assisted emission of such states is considered as the source for the linear increase in charge concentration at the p‐n interface with the applied reverse voltage. The high frequency capacitance‐voltage technique is used to study the charging and discharging of interface states in an MBE‐made sample at different temperatures and different biases. The experimental results show good agreement with the prediction of our model. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360725

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We study the formation and dynamics of normal domains in Rutherford‐type superconducting cables. We use an effective circuit model to account for the electric current redistribution process between the multifilamentary strands in the presence of a normal zone. We obtain and integrate numerically the diffusion equations for the temperature and the current‐density distributions in the cable. Our simulations show the formation of stable normal domains propagating along the cable. We derive an analytical expression for the threshold currentIdabove which the propagating normal domains exist. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360388

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have observed by experiment that the oxide growth rate on porous silicon is reduced to a minimum when the surface is treated with a proper amount of HF vapor. Fourier transform infrared spectroscopy and x‐ray photoelectron spectroscopy observations of the treated surface suggest that the oxide growth rate is closely related to the amount of the surface fluorides. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360389

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The properties of deep traps in undoped, Si‐, S‐, Se‐, and Te‐doped In0.5 Ga0.5 P layers grown on GaAs substrates by liquid phase epitaxy are investigated by deep level transient spectroscopy, thermally stimulated capacitance, and Hall measurements. Only one kind of deep trap is observed in undoped layer. Among the doped layers, it is only in the S‐doped layer that the deep trap concentration is increased and the persistent photoconductivity is observed. Furthermore, the deep trap properties in undoped and S‐doped layers are nearly the same. Considering the amount of residual S atom in the undoped layer, it is suggested that the deep trap in the undoped layer may result from the residual S impurity. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360390

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A new tunable source of the far‐infrared radiation based on intersubband electronic Raman scattering in semiconductor quantum wells is proposed. The gain and threshold of the proposed Raman oscillator are estimated and compared with the intersubband laser. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360391

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have recently succeeded in preparingb‐axis oriented YBa2Cu3Oythin films by laser metalorganic chemical vapor deposition and special thermal treatments. Theb‐axis orientation means that the CuO chain in the basal plane is perpendicular to the film surface, while thea‐axis orientation is parallel to the film surface. When oxygen is introduced after complete oxygen depletion aroundy≊6, we always obtaina‐axis oriented films. On the other hand,b‐axis oriented films can be obtained if the film whosec‐axis is parallel to the film surface is refilled with oxygen after medium oxygen reduction close to the orthorhombic‐tetragonal phase boundary. These phenomena can be explained by oxygen arrangement in Cu‐O basal planes caused by the stress between the deposited films and the substrates due to the difference in their thermal expansion coefficients. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360392

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The growth rate and the incorporation efficiency of dopants have been studied in the case of chemical vapor deposition of B‐doped polycrystalline diamond films. The deposition rate is found to decrease with the addition of diborane in the gas phase. This is correlated with a modification of the plasma chemistry as observed by emission spectroscopy (decrease in the H/H2, CH/H, and C2/H ratios with the addition of diborane). The concentration of boron incorporated in the films is observed to vary with the square of the boron concentration in the gas phase. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360393

出版商:AIP    

年代:1995

数据来源: AIP