Junction Electrical Characteristics Research Articles

Effect of Helium Ion Irradiation on the Tunneling Behavior in Niobium/Aluminum–Aluminum Oxide/Niobium Josephson Junctions

The study of the effects of high-energy particle irradiation on trilayer Josephson junctions has allowed us to investigate the influence of defects and interfacial intermixing on the junction electrical characteristics. In this paper, we investigated the influence of 2-MeV helium ion irradiation with doses up to 5.25 × 1016/cm2 on the tunneling behavior of Nb/Al-AlOx/Nb Josephson junctions. The modeling of the irradiation-induced chemical changes, combined with transmission-electron-microscopy characterization, indicates that over 2 nm of atomic intermixing occurs at all interfaces. Surprisingly, the quality of the tunneling characteristics is not significantly degraded, although some properties were affected: 1) The onset of the quasi-particle current characteristic of the electrodes' sum gap, Δ1 + Δ2, decreased from 2.8 to 2.6 mV; 2) the temperature onset of the Josephson current dropped from 9.2 K to 9.0 K; and 3) the normal resistance, Rn, increased by <; ~ 20%. The dependence of the Josephson current on the magnetic field was not significantly altered. Modeling using proximity theory indicated that the irradiation-induced changes in the current-voltage (I -V) characteristics are likely due to an increased drop in the order parameter near the barrier interface as a result of a reduced mean free path in the Al proximity layer from Nb and O contamination.

Thermal Stability of Nickel Silicide and Shallow Junction Electrical Characteristics with Carbon Ion Implantation

In this work, we investigated the impact of carbon ion implantation on the thermal stability of nickel silicide film and nickel-silicide-contact n+/p shallow junctions. A higher carbon ion implantation dose can prevent the nickel silicide film from agglomeration and phase transformation. However, good thermal stability does not necessarily lead to excellent junction current–voltage characteristics owing to the diffusion of nickel atoms. When the carbon ion implantation dose increases to 5×1015 cm-2, many crystal defects are created. Then, numerous nickel atoms diffuse along these defects into the junction depletion region during the silicide formation process, resulting in poor junction characteristics. The trade-off between thermal stability and junction electrical characteristics is discussed in this paper. Finally, two methods are suggested to solve the serious leakage current problem.

Oligoazomethine-doped planar tunnel junctions: Correlating molecular structure with junction electrical characteristics

We have investigated electrical properties of planar aluminum/aluminum oxide/silver tunnel junctions modified with phenyl-based azomethine oligomers. Normalized differential conductance, NDC (NDC=σV/σV=0, where σ=dI/dV), of the junctions increases with oligomer length. At a bias of 2 V, azomethines with three phenyl rings exhibit NDCs that are on average more than an order of magnitude greater than those of unmodified oxide junctions. Differential conductances of junctions modified with azomethines increase more rapidly with temperature than those of plain oxide junctions. Our results are consistent with a model in which both increased conjugated length of the sandwiched organic layer and a molecule/metal interface lead to a lowering of the barrier profile outside the aluminum oxide tunnel region.

GaN PN junction issues and developments

Critical nitride-based p- n junction issues relating to wide bandgap bipolar device performance include minority carrier lifetime, defect related current characteristics and ohmic contact properties. Recent developments in p-GaN deposition processes resulted in GaN p- i- n UV photodetectors with improved deep UV responsivity, visible light rejection and shunt resistance characteristics. From the device data, the electron diffusion length in p-GaN doped at 1·10 18 cm −3 was estimated to be 790 Å, and the minority carrier lifetime in the p-GaN was estimated to be 24 ps to 0.24 ns. Improved junction electrical characteristics were achieved using MBE deposition on GaN buffers grown by MOCVD. NiAu ohmic contacts were also made to p-GaN with specific contact resistances less than 10 −4 Ω·cm 2.

Unexpected geometrical anodization effect in the fabrication of Nb/Al-oxide/Nb junctions

In our research on the fabrication of Nb/Al-oxide/Nb mixer elements, we have discovered an unexpected effect which is attributable to the geometry of the mixer. We have found that the electrical quality of anodically sealed junctions fabricated in our laboratory depends strongly on the geometry of the base electrode. For example, it is possible to design a series array of junctions using two geometries of base electrode features and obtain poor junction electrical characteristics with one type of base feature and excellent characteristics with the other. The role of Nb film stress, junction size and placement on the base electrode feature, wiring interconnection process and anodization conditions in this effect have been studied.

Transmission Electron Microscopy Microstructure Characterization of YBCO/SrRuO3/YBCO Josephson Junctions

Abstract: The microstructure of YBCO/SrRuO3/YBCO junctions in the edge geometry have been studied by high resolution electron microscopy. Various defects in the YBCO and SrRuO3 films are observed and analyzed. The most striking defects in the c-axis-oriented YBCO film are a-axis particles, which cause bending and interruption of lattice planes as well as high steps and cracks in the subsequent layers. The SrRuO3 layer in the ramp-edge junction region consists of small domains with slightly different orientations. This leads to the formation of steps on its surface and large variation in SrRuO3 thickness. Mechanisms for forming this defective layer are suggested based on the growth mode and the crystal structure of SrRuO3. We find evidence for strain fields at the SrRuO3/YBCO interface. The oxygen deficiency in YBCO caused by this interface strain may to a large part be responsible for the excess resistivity of this junction. In addition to the defective SrRuO3 layer, the occurrence of various defects in the junction area, including Y2O3 and a-axis YBCO particles, seem to be the cause for the wide scatter in the junction electrical characteristics. The formation of steps and large thickness variation in the barrier layer may be the reason for the rather large critical thickness of the SrRuO3 superconductor-normal-superconductor (SNS) junction. In addition to the junction interfaces, the microstructure of SrRuO3/LaAlO3 and SrRuO3/SrTiO3 interfaces have also been studied.

Determination and observation of electronic defect levels in CuInSe2 crystals and thin films

The effects of heat and surface treatments used in the fabrication of CuInSe2 (CIS) single-crystal and thin-film solar cells are investigated, and the associated dominant defect states are identified using high-resolution photoluminescence (PL) and deep-level transient spectroscopy (DLTS) measurements. The results are correlated with junction electrical characteristics, and comparisons between thin films and single crystals are established. For the first time, direct evidence for several major defect types (Cu vacancies, Cu at In sites, and In at Cu sites) responsible for the majority-carrier type of the CIS is presented based upon spectroscopic atomic imaging of the n- and p-type semiconductor surfaces. Radiative recombination levels of extrinsic origin resulting from the surface processing (including polishing, etching, and annealing) were detected in the near surface region of the CIS single crystals, but not in the thin-film material having the same composition. The energy locations and depth of these states are responsible for the formation of an interfacial layer that is confirmed from frequency-dependent capacitance–voltage (C–V) data. The DLTS measurements on single-crystal and thin-film heterostructure {i.e., [Cd,Zn]S/CIS} devices (of nearly identical chemical compositions) have also confirmed the presence of a dominant trap level in the 270-meV region above the valance band. However, the trap density is some two orders of magnitude lower in the thin-film device, giving evidence that this processing-related defect level is responsible for the inferior performance of the single-crystal solar cells.

OMCVD-grown InP/GaInAs heterojunction bipolar transistors

We report the growth and fabrication of the first InP/ GaInAs heterojunction bipolar transistor by OMCVD. Fabricated transistors exhibited near-ideal emitter-base junction electrical characteristics over ten orders of magnitude, enabling us to obtain transistor current gains as high as 5000 at current densities as low as 1000 A cm−2. This is the highest current gain reported for this material system.

Solar Energy Conversion: The Solar Cell

Part 1 Energy needs - energy sources: consumption conventional sources of energy alternative energy sources nuclear fusion solar energy temperature differences thermodynamics ocean temperature-difference generators solar-thermal solar-electric references. Part 2 The sun and sunlight: sunlight geometrical effects weather light collection lens systems mirrors optical materials maximum optical concentration references. Part 3 Semiconductors: crystal structure quantum mechanics and energy bands electrons and holes currents recombination and carrier lifetime junctions references. Part 4 Light-semiconductor interaction: reflection light interaction preliminary material selection absorption reflection and absorption references. Part 5 Basic theoretical performance: local electric fields PN junction electrical characteristics heterojunction electrical characteristics electrical characteristics of schottky junctions open circuit voltage and short circuit current optimum power conditions references. Part 6 Solar cell configuration and performance: optical orientation device design - minority carrier collection device design - saturation current device design - series resistance solar cell performance - discussion references. Part 7 Advanced approaches: temperature effects heat flow within a solar cell optical concentration - photocurrent performance under concentration references. Part 8 Advanced approaches - II: second stage solar power systems third generation solar cell systems miscellaneous approaches references. Part 9 Polycrystalline and amorphous solar cells: polycrystalline solar cells cadmium sulfide/copper sulfide copper indium selenide (CIS) polycrystalline silicon thin film cadmium telluride other possibilities for polycrystalline solar cells final comments on polycrystalline solar cells amorphous material based solar cells amorphous silicon concluding remarks references. Part 10 Concluding thoughts: economics electrical energy storage the system final words references.