Zero-bias Resistance Research Articles

Modeling of electrical characteristics of midwave type II InAs∕GaSb strain layer superlattice diodes

This paper reports the results of modeling of electrical characteristics of midinfrared type II InAs∕GaSb strain layer superlattice (SLS) diode with p-on-n polarity. Bulk based model with the effective band gap of SLS material has been used in modeling of the experimental data. Temperature dependence of zero-bias resistance area product (R0A) and bias dependent dynamic resistance of the diode have been analyzed in detail to investigate dark current contributing mechanisms that are limiting the electrical performance of the diode. R0A of the diode is found to be limited by thermal diffusion currents at higher temperatures and Ohmic shunt resistance contribution limits it at low temperatures ∼82K.

Low-Noise Mid-Wavelength Infrared Avalanche Photodiodes

Mid-wavelength infrared (MWIR) p +–n −–n + avalanche photodiodes (APDs) were fabricated using two materials systems, one with mercury cadmium telluride (HgCdTe) on a silicon (Si) substrate and the other with an indium arsenide/gallium antimonide (InAs/GaSb) strained layer superlattice (SLS). Diode characteristics, avalanche characteristics, and excess noise factors were measured for both sets of devices. Maximum zero-bias resistance times active area (R 0 A) of 3 × 106 Ω cm2 and 1.1 × 106 Ω cm2 and maximum multiplication gains of 1250 at −10 V and 1800 at −20 V were measured for the HgCdTe and the SLS, respectively, at 77 K. Gains reduce to 200 in either case at 120 K. Excess noise factors were almost constant with increasing gain and were measured in the range of 1 to 1.2.

Avalanche Mechanism in p +-n −-n + and p +-n Mid-Wavelength Infrared Hg1−x Cd x Te Diodes on Si Substrates

Hg1−x Cd x Te mid-wavelength infrared (MWIR) p +-n −-n + and p +-n − avalanche photodiodes (APDs) with a cut-off of 4.9 μm at 80 K were fabricated on Si substrates. Diode characteristics, avalanche characteristics, and excess noise characteristics were measured on two devices. Temperature-dependent diode and avalanche characterization was performed. Maximum 3 × 106 Ω cm2 and 9 × 105 Ω cm2 zero-bias resistance times active area (R 0 A) products were measured for the p +-n −-n and p +-n devices at 77 K, respectively. Multiplication gains of 1250 and 410 were measured at −10 and −4 V for the p +-n −-n + and p +-n APDs at 77 K, respectively, in the front-illumination mode with the help of a laser with an incident wavelength of 632 nm. The gains reduce to 200 and 50 at 120 K, respectively. The excess noise factor in all APDs was measured to be in the range of 1 to 1.2.

Electrical and optical properties of bismuth telluride/gallium nitride heterojunction diodes

Semiconducting bismuth telluride has a band gap energy of about 0.15eV at room temperature and is a good material for middle wavelength IR (MWIR) detection [S.K. Mishra, S. Satpathy, O. Jepsen, J. Phys. Condens. Matter, p. 461]. We have grown bismuth telluride thin films on gallium nitride (on sapphire) by pulsed laser deposition at a substrate temperature of 300°C. The structural characteristics and surface morphology of the films were studied by X-ray diffraction and scanning electron microscopy, respectively. The chemical composition of the as-deposited bismuth telluride thin films was determined by X-ray photoelectron spectroscopy and was found to be different from that of the bulk target, changing from stoichiometric Bi2Te3 to bismuth rich. A bismuth rich p-Bi2Te3/n-GaN/Al2O3 heterojunction was fabricated for photovoltaic detection of low energy photons. The wide band gap semiconducting n-GaN layer and the Al2O3 substrate act as a window for IR transmission. A sensitive IR photoresponse of the heterojunction is obtained by back-side illumination. The photocurrent measured is 0.18μA according to the irradiation change in the current–voltage characteristics. The current–voltage characteristics allow us to evaluate the series resistance (Rs), zero-bias resistance (R0) and ideality factors (n) of the junctions. Our results have suggested that bismuth telluride is a potential candidate for photovoltaic mid-infrared detection.

Evaluation of implanted InSb p+n diodes passivated with composite anodic oxide/SiOxstack

This investigation presents detailed characteristics of an implanted planar InSb p+n diode with a junction area scaled down to 20 × 20 μm2. Low-temperature photo-chemical vapor deposition oxide stacked with an optimized thin anodic film, instead of a gate control structure, is used to control the planar surface potential of the implanted p+n diode under the weak inversion condition on the n-type surface and under weak accumulation on the p-type surface. The zero-bias resistance–area product is 7.6 × 104 Ω cm2 at 77 K. To the best of the authors' knowledge, this result represents the best performance of a small-area and implanted planar diode to date. The dark current is controlled by an internal shunt conduction mechanism, which seems to be related to the defects that are produced by the implantation. Low leakage current and high breakdown voltage have proven the feasibility of the composite anodic oxide/SiOx that is stacked as the passivation structure in small-pixel InSb p+n photodiodes for focal plane array applications. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Phase diffusions due to radio-frequency excitations in one-dimensional arrays of superconductor/ insulator/superconductor junctions

The dc response of one-dimensional (1D) arrays of superconductor/insulator/superconductor (SIS) junctions under radio-frequency (RF) irradiation has been experimentally studied. The zero-bias resistance as a function of RF amplitude in the low-frequency regime shows an oscillatory behaviour, and can be explained using the phase fluctuation model for Cooper-pair tunnelling. It follows that an effective classical detector theory is applicable and the oscillation period can be compared with the superconducting gap. The results suggest a primary and direct RF detection scheme using 1D SIS junction arrays.

Simulation and Optimization of Heterojunction Photodetectors Based on Mercury Cadmium Telluride

In the present paper, the performance of n-on-p heterojunction photodetector based on Hg 1-x Cd X Te (MCT) has been analyzed theoretically for operation at 4.2 μm. The energy band diagram, electric field profile, carrier concentration, dark current, dynamic resistance, quantum efficiency and detectivity have been calculated and optimized as a function of different variables such as device thickness, reverse voltage and operating wavelength to optimize the performance of p-n heterojunction photodetector at room temperature. The dependence of the p-n junction position within heterostructure on the bandgap energy profiles and the influence of doping concentration on photodetector parameter have been studied. The dark current-voltage characteristics and dynamic resistance versus voltage characteristics has been simulated. The optical characterization takes into account the quantum efficiency and detectivity of the heterojunction photodetector. Results of our simulated study reveal that under suitable biasing condition, the photodetector offers a dark current, I D ≈10 -11 A, a zero-bias resistance, R≈1.32 x 10 7 Ω, quantum efficiency η ≈ 74% and detectivity D* ≈ 8.3 x 10 10 mHz 1/2 /W.

Electrochemical performance of lanthanum calcium cobalt ferrite cathode interfaced to LAMOX electrolyte

Lanthanum calcium cobalt ferrite (LCCF), a potential cathode composition for the LAMOX electrolyte, is studied on its electrocatalytic performance in oxygen reduction reaction (ORR) using impedance spectroscopy. Nyquist plots of LCCF impedance at 600–800 °C display two arcs, in which the low-frequency arc is constantly larger than the high-frequency arc. When interfaced to the electrolyte containing 20 mol% tungsten, the ORR polarization resistance of LCCF exhibits a strong temperature dependency whose activation energy increases with increasing Co content, 190 (10 mol%)–220 (90 mol%) kJ mol − 1 . Among the cathode compositions, LCCF82 (80 mol% Co) exhibits the best catalytic performance. Its zero-bias ORR resistance is 242.4 at 600 °C, 0.845 Ω cm 2 at 800 °C, along with the capacitance 7.79 (600 °C), 14.93 mF cm − 2 (800 °C). The ORR resistance of LCCF82 decreases with increasing dc bias at 600 and 700 °C, hardly changes at 800 °C. The electrocatalytic activity of LCCF82 is also influenced by the tungsten content of its interfacing electrolyte. The exchange current density of LCCF82 correlates positively with the electrolyte ion conductivity which increases with decreasing tungsten content.

Observation of gate-controlled superconducting proximity effect in microfabricated thin graphite films

We investigated the influence of the oxygen plasma etching on the electron transport in thin graphite films. The semimetallic temperature dependence of zero-bias resistance was observed for samples microfabricated with both Al mask and resist mask, but the possible damage by e-beam irradiation was observed in films with Al mask. In thin graphite films microfabricated by O2 plasma with resist mask, the proximity-induced superconductivity was observed and the critical supercurrent and temperature strongly depend on the gate voltage.

Characterization of high-temperature PbTe p-n junctions prepared by thermal diffusion and by ion implantation

Two types of high-quality PbTe p-n junctions, prepared by thermal diffusion of In4Te3 gas [thermally diffused junction (TDJ)] and by ion implantation [implanted junction (IJ)] of indium (In-IJ) and zinc (Zn-IJ), have been characterized. Capacitance-voltage and current-voltage characteristics have been measured over a temperature range from ∼10to∼180K. The saturation current density J0 in both diode types was ∼10−5A∕cm2 at 80K, while at 180K, J0∼10−1A∕cm2 in TDJ and ∼1A∕cm2 in both IJ diodes. At 80K, the reverse current started to increase markedly at a bias of ∼400mV for TDJ and at ∼550mV for IJ. The ideality factor was about 1.5–2 for both diode types at 80K. Both diode types were linearly graded. The height of the junction barrier, the concentration and the concentration gradient of the impurities, and the temperature dependence of the static dielectric constant have been determined. The zero-bias resistance times area product (R0Ae) at 80K is 850Ωcm2 for TDJ, 250Ωcm2 for In-IJ, and ∼80Ωcm2 for Zn-IJ, while at 180K, R0Ae∼0.38Ωcm2 for TDJ and ∼0.1Ωcm2 for both IJ diodes. The estimated detectivity is D*∼1011cmHz1∕2∕W at T=80K, determined mainly by background radiation, while at T=180K, D* decreases to 5×109–1010cmHz1∕2∕W and is determined by the Johnson noise.

Fabrication and passivation of GaSb photodiodes

A novel Zn diffusion technique in n-GaSb substrate from a low temperature chemical bath deposited ZnS layer has been developed to obtain high breakdown voltages. Junctions formed by this technique have breakdown voltages of ∼18.5V, low reverse leakage current (0.01–0.03A/cm2 at -3V), excellent reverse current saturation and ideality factor of ∼1.3. The high breakdown voltages obtained are due to the co-doping of zinc and sulfur from the ZnS film. Sulfur forms shallow and deep levels that compensate the p-doping of zinc. The non-linear relation of the inverse of the zero-bias resistance area product (1/R0A) versus perimeter to area ratio (P/A) in these diodes indicates surface leakage is the dominant leakage mechanism. CdS has been used to passivate the mesa photodiodes. After passivation, the 1/R0A product reduces from 0.3 to 0.02Ω-1cm-2 for a 150μm diameter device. The 1/R0A product is also independent of the diode dimension confirming effective passivation. ZnS surface passivation on the mesa walls is not effective and is found to increase the leakage current.

Beryllium compensation doping of InAs∕GaSb infrared superlattice photodiodes

Capacitance-voltage measurements in conjunction with dark current measurements on InAs∕GaSb long wavelength infrared superlattice photodiodes grown by molecular-beam epitaxy on GaSb substrates are reported. By varying the beryllium concentration in the InAs layer of the active region, the residually n-type superlattice is compensated to become slightly p type. By adjusting the doping, the dominant dark current mechanism can be varied from diffusion to Zener tunneling. Minimization of the dark current leads to an increase of the zero-bias differential resistance from less than 4to32Ωcm2 for a 100% cutoff of 12.05μm

Low-temperature Schottky barrier tunneling inInSb∕InxAl1−xSbquantum well heterostructures

We report low-temperature $I(V)$ measurements taken on small area surface metal contacts to $\mathrm{In}\mathrm{Sb}∕\mathrm{In}\mathrm{Al}\mathrm{Sb}$ quantum well material in the temperature range $4.5--100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. We obtain Schottky barrier $J(V)$ data under reverse bias and analyze the transport observed by using a tunneling model derived from the three-dimensional density of states, showing close correlation for the majority of devices measured. We consider the ``Rowell'' analysis [Tunneling Phenomena in Solids, edited by E. Burnstein and S. Lundqvist (Plenum, New York, 1969), p. 273] of the zero-bias resistance ${R}_{0}(T)$ and differential conductance $G(V)$ for determining the dominant transport mechanism. Two distinct temperature dependences are observed in the ${R}_{0}(T)$ data, a weak insulatorlike dependence identifying true single-step tunneling and a strong nonlinear dependence, which we attribute to defect assisted multistep tunneling. Effective barrier parameters are extracted by fitting the $G(V)$ data with a Brinkman-Dynes-Rowell model [J. Appl. Phys. 41, 5 (1970)] for carrier tunneling.

In As Sb ∕ Ga Sb heterostructure based mid-wavelength-infrared detector for high temperature operation

The properties of a midinfrared photodetector, based on a lattice matched n-N InAs0.91Sb0.09∕GaSb type-II heterostructure, were investigated. The relatively simple two layer structure shows very promising characteristics for sensitive and dual color infrared detection. I-V characteristics and spectral response were measured at the temperature range of 10–300K. High zero-bias resistance area product R0A of 2.5Ωcm2 was obtained at room temperature. The measured background limited infrared photodetection temperature was 180K corresponding to 4.1μm cutoff. Shot and Johnson noise limited detectivities corresponding to InAsSb absorption were measured to be 1.3×1010 and 4.9×109cmHz1∕2W−1 at 180 and 300K, respectively. An enhanced optical response with gain larger than unity was observed below 120K. Bias tunable dual color detection was demonstrated at all measured temperatures.

Gate-Controlled Superconductivity in a Diffusive Multiwalled Carbon Nanotube

We have investigated electrical transport in a diffusive multiwalled carbon nanotube contacted using superconducting leads made of an Al/Ti sandwich structure. We find proximity-induced superconductivity with measured critical currents up to I(cm)=1.3 nA, tunable by the gate voltage down to 10 pA. The supercurrent branch displays a finite zero bias resistance which varies as R(0) proportional to I(cm){-alpha} with alpha=0.74. Using IV characteristics of junctions with phase diffusion, a good agreement is obtained with the Josephson coupling energy in the long, diffusive junction model of A. D. Zaikin and G. F. Zharkov [Sov. J. Low Temp. Phys. 7, 184 (1981)].

247 nm solar-blind ultraviolet p-i-n photodetector

We describe solar-blind p-i-n photodetectors based on short period superlattices of AlN∕Al0.08Ga0.92N. The devices are grown using gas source molecular beam epitaxy with ammonia on transparent sapphire substrates. The cutoff wavelength for the device is 247nm. For diodes with 150μm diameter mesas and sidewall surfaces passivated in oxygen plasma, we obtain extremely low dark leakage current of ∼3pA∕cm2 and high zero-bias resistance of ∼6×1014Ω. At 10V reverse bias the observed responsivity is 62mA∕W.

Contribution of dislocations to 1/ f noise in mercury cadmium telluride infrared photovoltaic detectors

Contribution of dislocations to 1/ f noise has been investigated by analysing the temperature dependence of the noise, dark current and zero-bias resistance–area product of mercury cadmium telluride (HgCdTe) diodes. It is shown that irrespective of the type of diode, i.e. n-on-p or p-on-n, dislocation contribution to 1/ f noise can be described by i n = 1 × 10 −2 I sh and i n = 6 × 10 −4 I sh for planar and mesa configurations respectively, where, I sh is the current conducted through the dislocations in the base of the diode. A physical model, consistent with the shunt resistance behaviour of dislocations, has been proposed to understand the role of dislocations in enhancing 1/ f noise of these diodes.

In situ resistance measurements of epitaxial cobalt silicide nanowires on Si(110)

We have performed in situ resistance measurements for individual epitaxial CoSi2 nanowires (NWs) (approximately 60 nm wide and 5μm long) formed on a Si(110) surface. Two- and four-point probe measurements were done with a multitip scanning tunneling microscope at room temperature. The NWs were well isolated from the substrate by a Schottky barrier with zero-bias resistance of 107Ω. The resistivity of the NWs was 30μΩcm, which is similar to that for high-quality epitaxial films. The NW resistance was essentially unchanged after exposure to air.

Resistance measurements of metallic silicide nanowires on a Si substrate with a four-tip scanning tunneling microscope

We have measured electrical resistance of individual epitaxial CoSi2 nanowires (NWs) formed on a Si(110) surface in situ in ultrahigh vacuum, by two-, three-, and four-point probe methods using a multi-tip scanning tunneling microscope at room temperature. The NWs were electrically isolated from the substrate by a Schottky barrier in-between with zero-bias resistance of approximately 107 Ω. Contact resistance between a W tip and a NW was as small as several tens Ω. The resistivity of the NWs was ca. 30 μΩcm, which is similar to that of high-quality epitaxial CoSi2 films. The oxidation of the NW surface had negligible influence on the resistance, meaning marginal carrier scattering at the NW surface. [DOI: 10.1380/ejssnt.2005.362]

Phase slips in superconducting films with constrictions

A system of two coplanar superconducting films seamlessly connected by a bridge is studied. We observe two distinct resistive transitions as the temperature is reduced. The first one, occurring in the films, shows some properties of the Berezinskii-Kosterlitz-Thouless (BKT) transition. The second apparent transition (which is in fact a crossover) is related to freezing out of thermally activated phase slips (TAPS) localized on the bridge. We also propose a powerful indirect experimental method allowing an extraction of the sample's zero-bias resistance from high-current-bias measurements. Using direct and indirect measurements, we determined the resistance $R(T)$ of the bridges within a range of {\em eleven orders of magnitude}. Over such broad range, the resistance follows a simple relation $R(T)=R_N \text{exp} [-(c/t)(1-t)^{3/2}]$, where $c=\Delta F(0) / kT_c$ is the normalized free energy of a phase slip at zero temperature, $t=T/T_c$ is normalized temperature, and $R_N$ is the normal resistance of the bridge.