PHASE－LOCKED 2－D JOSEPHSON JUNCTION ARRAYS AS SUBMILLIMETER OSCILLATORS

This letter presents the results of numerical simulations for phase-locked 2-D Josephson junction array oscillator.The simulation result shows that the junctioons of 2-D array can mutually phase-locked in a considerable area if the parameters can be carefully selected.The oscillators are formed with up to 33 identical Nb/AlOx/Nb junctions,and the junctions are connected with Nb microstrip resonators.Optimum structure parameters for ocsillator circuit design can be obtained with these simulation results.     

Fabrication of Josephson tunnel junction with suspended metal mask

 A small area Josephson tunnel junction is fabricated with the suspended metal mask made of ordinary razor blades.The junction overlap is formed by two successive evaporations of superconductor materials at oblique angles.The advantages of this technique are that the fabrication processes can be performed continuously without opening the evaporation chamber and also it is suitable for making a small area tunnel junctions.The Ⅰ-Ⅴ characteristic of a tunnel junction made by this technique has been taken at 4.2K.     

Microwave properties of silicon junction tunnel diodes grown bymolecular beam epitaxy

The bias dependence of the single-port microwave reflection gain of 15 μm-diameter Si Esaki tunnel diodes, grown by molecular beam epitaxy, was studied as a function of frequency. A simple equivalent circuit accurately modeled the data and yielded the forward-bias junction capacitance, which cannot be obtained by conventional low frequency capacitance-voltage techniques. The diodes were highly-doped step p-i-n junctions and exhibited a peak current density of 16 kA/cm ². The microwave reflection gain and cut-off frequency were 12 dB land 1.6 GHz, respectively, with a speed index (slew rate) of 7.1 V/ns     

Some observations from interrupted lifetest of GaInAsP/InP inverted-rib laser diodes

Conventionally, lifetests of semiconductor laser diodes usually involved operating the devices continuously at either constant power output or drive current, with periodic recording of their characteristics. In this paper, some effects arising from interrupted lifetest of 1.3 m GaInAsP-InP inverted-rib laser diodes are reported. This unconventional lifetest method involves constant power biasing at 4 mW/facet and 8 mW/facet respectively at 50°C, followed by a period during which the lifetest is interrupted and the devices left unbiased at room temperature. Subsequently, the devices were put back on constant power biasing at 50°C. Among a number of parameters, pronounced reduction in the threshold current, current for 4 mW/facet and 8 mW/facet were observed, indicating strong recovery effects commencing from the time when the life-test was interrupted. Redistribution of mobile defects in the cladding layer is postulated to be the cause of the degradation recovery, and the data supports the occurrence of an aging-current dependent defect annihilation mechanism. Such recovery effects have so far been observed to occur only in the GaInAsP-InP inverted-rib devices.     

Numerical simulation of tunnel diodes for multi‐junction solar cells

This work presents efforts to simulate numerically the current voltage (IV) curve of a III–V based Esaki tunnel diode. Using a tunneling model, which takes into account the full nonlocality of the barrier, a good agreement between measured and simulated IV curves of a GaAs tunnel diode was achieved. The influence of a series resistance effect as well as the importance of trap assisted tunneling (TAT) could be shown. In addition, we present a two‐dimensional model of a III–V multi‐junction solar cell including the numerical model of the investigated Esaki tunnel diode. Copyright © 2008 John Wiley & Sons, Ltd.     

Surface aspects of the thermal degradation of GaAs p-n junction lasers and tunnel diodes

Owing to the similarity of the junction widths and doping levels in epitaxially formed GaAs lasers and conventional tunnel diodes, the gradual degradation of the latter under use might be expected to be intensified in the case of lasers operating under high duty cycle or CW conditions. It was found that the current-voltage characteristics of both the lasers and tunnel diodes underwent considerable thermal degradation even when no bias was applied, and that the degradation was limited to surface or "junction edge" effects. The degradation of the current-voltage characteristic was correlated with degradation in the light output under forward bias. It was concluded that degradation under forward bias was also a surface effect induced by heating rather than by deterioration of the junction in the bulk, as commonly believed. Methods of controlling the degradations are discussed.     

Millimeter-wave point-contact and junction diodes

Millimeter-wave "point-contact" diodes are classed as conventional point-contact diodes (and modifications on them), which depend primarily upon a point-contact metal-semiconductor junction for their rectification properties; or as junction diodes with point-contact geometry, which are small-area millimeter-wave adaptations of the p-n junction diodes, normally made for use at lower frequencies by alloying, diffusion and other techniques. In a general way, techniques used in the fabrication of these various diodes are described; then the uses to which they have been put is detailed, and the best reported performance characteristics in various millimeter-wave applications are compared. Emphasis is put on demonstrated performance, but highly experimental and tentative laboratory results are freely quoted. Included are discussions of 1) conventional point-contact diodes of various semiconductors; 2) diodes having point-contact geometry but exhibiting electrical properties approximating those of alloyed and diffused p-n junctions, diodes made by planar techniques, a "thermoelectric effect hot carrier" diode, point-contact photodetectors and photoemitters; and 3) a millimeter-wave avalanche transit-time oscillator diode. The use of these diodes as millimeter-wave detectors, amplifiers, oscillators, harmonic generators, and modulators is considered.     

Silicon-coupled Josephson junctions and super-Schottky diodes with coplanar electrodes

Superconducting devices with coplanar electrodes have been fabricated using electron-beam lithography to define the smallest feature. The devices each consist of two Pb-In alloy electrodes, 20 µm wide, deposited on a clean, degenerately doped silicon substrate. The two electrodes are separated by a thin (100-300-nm) gap. Electron-beam lithography is used to define the gap, and sputter etching to remove the underlying alloy film. Depending on the width of the gap and the condition of the metal-semiconductor interface, these devices displayed either Josephson or super-Schottky diode behavior. The Josephson devices show a high degree of robustness and hadI_{c}Rproducts in the range 200-800 µV at 4.2 K. The super-Schottky diodes had current sensitivities S in the range 1000-1300 V^-1when measured at 4.2 K.     

Josephson junction millimeter microwave source and homodyne detector

A millimeter and submillimeter microwave source is described in which a point-contact Josephson junction is used as both the emitter and as a homodyne detector of the microwave radiation. The microwave radiation is conveyed from the Josephson junction to the room-temperature environment outside the Dewar of liquid helium by an oversize waveguide. A room-temperature Fabry-Perot resonator refocuses the radiation on the oversize waveguide which returns the radiation to the emitting junction which also serves as a coherent detector with sensitivity 10^-15W/√Hz. The detector is sufficiently sensitive that the emitted power of 10^-12W can be detected with high signal-to-noise ratio. Power required by the junction is of the order 10^-6W from the bias supply. For the experiments reported, the wavelength of the emission could be varied over discrete wavelengths between 1.1 and 2.6 mm by varying the voltage bias across the junction. These wavelengths corresponded to the resonant frequencies of a cavity tightly coupled to the Josephson junction, and the frequencies can be changed by modifying the geometry of the cavity.     

High-frequency silicon-aluminum alloy junction diodes

Silicon-aluminum alloy junction diodes have been made that have rectifying properties up to frequencies of 500 megacycles per second. Recovery times from storage effects are of the order of 0.1 microsecond.     

Non-linear analysis of an S-I-S Josephson junction

The simplest model of an S-I-S Josephson junction is analysed by simulation in order to understand its switching behaviour. This model is assumed to have a parallel quasi-particle tunnelling current component, which is non.linear and ideal in the BCS sense. Fundamental properties, such as I _min and V _min, which specify hysteretic behaviour, as well as rise and fall times for switching, are calculated as functions of parameters β_c = 2ΠI _m0 R _n ² C/Φ₀ and γ = R _L R _n. How an AC Josephson current spoils the stability of a non-zero voltage state is discussed for the first time.     

Disappearance of Fiske steps in Josephson fluxonic diode and Josephson fluxonic bipolar junction transistor

Fiske steps which are normally present in the I-V curve of Josephson junctions disappear if the junction is subjected to a magnetic field which reverses its direction at the center of the device as in Josephson fluxonic diode. Experimental results for small and long Josephson junctions are provided. It is proposed that the reversing magnetic field sets extra conditions at the center of the junction which makes the creation of standing electromagnetic waves impossible.     

Optimization of the double-barrier Josephson junction switching dynamics

The switching dynamics of a double-barrier Josephson junction is analyzed as a function of the microscopic properties of its electrodes. In particular, it is found that the nonstationary behavior of the Josephson phase difference is very sensitive to dissipation mechanisms acting inside the intrinsic shunt. The leading factor that determines the dissipation is the local electron density of states N(E) inside the electrodes. The roles of junction geometry, electrode purity, and interface quality are discussed and how they affect the details of N(E), hence the resulting phase dynamics. The microscopic analyses allow optimization of the performance of double-barrier Josephson junction-based rapid-single-flux-quantum circuits in two ways: 1) decreasing the switching time of Josephson elements and 2) reducing the excess wiring. Such an analysis is facilitated with the aid of a lumped circuit representation which generalizes the nonlinear resistive-shunted-junction model.     

Millimeter wave response of Nb-Pb-Nb planar Josephson junction

The response characteristics of Nb-Pb-Nb planar Josephson junction under millimeter wave radiation is discussed. We could observe the third Shapiro step.     

Niobium oxide-barrier tunnel junction

We describe the fabrication and electrical characteristics of niobium oxide-barrier tunnel junctions having counterelectrodes of either Pb alloys or Nb. The conditions necessary to obtain good tunnel barriers are discussed in detail. These include RF plasma etching of the Nb film before oxidation, the oxidation step itself and, in the case of Nb counterelectrodes, exposure of the oxide to an RF plasma of N2containing traces of hydrocarbon. The single-particle current of Nb/Pb junctions at 4.2 K is close to the value calculated from BCS theory in the voltage range0 < V < 2mV. With Nb counterelectrodes the subgap current is higher, but in the best examples it is comparable to Nb/Pb at voltages below 1 mV. Finally, it is shown that the junctions exhibit outstanding stability during storage, annealing, and thermal cycling between room temperature and 4.2 K.     

Switching response of graded-base PN junction diodes

This paper extends the earlier analysis by Kingston of the switching response of a uniform-base diode to a graded-base diode. It concerns the time required to switch a diode from a forward-biased to a reverse-biased condition. The current transient can be separated into two phases: 1) the constant current phase during which the carrier density at the junction changes gradually from a forward-biased to a reverse-biased condition, and 2) the nonconstant current phase during which the injected carriers stored in the base region gradually disappear. In the present analysis, it is found that in a graded-base diode where the impurity concentration decreases from the emitter junction towards the base contact, the time for the constant current phase is greatly shortened because of favorable initial carrier distribution. The effect is already significant if the impurity concentration changes by a factor from 3 to 1 from the emitter junction to the base contact. To shorten the nonconstant current phase, however, a much larger change of impurity concentration, say of the order from 500 to 1, from the emitter junction to the base contact is needed.     

The SNS Josephson junction with a third terminal

It is shown that a current introduced directly into the N layer of an SNS Josephson junction whose width is much greater than ξNenters the two superconductors dividing in the ratio of the resistances encountered. The device acts as a two-terminal device with an auxiliary current divider.     

Scanning-electron-beam annealing of ion-implanted p-n junction diodes

Scanning-electron-beam annealing of ion-implanted silicon p+-n junctions over a range of beam power and exposure conditions is described. Electrical measurements have shown that electron-beam annealing can produce diode characteristics close to those of similar thermally annealed structures.