Прецизійний терморегульований комплекс кріогенної апаратури для дослідження вольт-амперних характеристик тунельних контактів надпровідних матеріалів

Characteristics of Pt Schottky contacts on hydrogen peroxide-treated n-type ZnO(0001) layers

An analytical solution for the current-voltage characteristics of a metal-semiconductor contact with a Mott barrier is derived with allowance made for the space charge of carriers in the n+-i junction. The main assumption used in solving the Poisson equation is that the bulk doping of the i layer is ignored. The dependences of the electric current on the voltage are calculated for the characteristic cases of the thermionic emission and diffusion mechanisms of charge transfer. In contrast to the classical Mott result, the inclusion of the space charge of carriers in the calculation limits the increase in the electric current at a forward bias and decreases the nonlinearity of the current-voltage characteristics.

The structure and current-voltage characteristics (CVCs) of copper-tungsten electric contacts deposited using a Plasma Focus facility are studied. It is shown that the reduced contact resistance is ∼0.4 × 10−6 Ω cm2 at 300 K and ∼0.4 × 10−7 Ω cm2 at 80 K, which meets the highest requirements for ohmic contacts in electrical installations and semiconductor electronics. The formation of microcracks on the surface of tungsten exposed to high-speed plasma streams has no significant impact on the contact resistance. Under the effect of high pressure, a melt of copper penetrates deep into tungsten along the cracks, solidifies, and thereby forms zones of high conductivity. The soldering of electric contacts with tin solder leads to CVC deviation from linearity at 80 K. A probable cause of this is the formation of SnO2-copper Schottky barriers on the surface of Cu-W contacts.

Damage in silicon induced by dry etching processes is found to affect the kinetics of formation and the current-voltage characteristics of Pd2Si contacts formed in the 225–275 °C range. We show in this work that low-energy ion-beam etching (IBE) with Ar+ ions in the energy range 0.4–1.4 keV modifies the diffusivity controlling the silicide formation process. For the energy range and beam parameters studied, the diffusivity is found to increase approximately linearly with the IBE energy, while the activation energy of the silicide formation process does not change significantly. Although the depth of the damaged layer, prior to silicide formation, is not greater than 200 or 300 Å as detected by the Rutherford backscattering technique, the damage detected by the current-voltage characteristics of the Pd2Si/Si system is not removed by the silicide growth, particularly in the case of n-type silicon. A comparison of current-voltage characteristics for reactive-ion etched silicon and ion-beam etched Si demonstrates that the damage incurred in reactive-ion etching is also not consumed by low-temperature Pd2Si formation.

Summary form only given. Current-voltage characteristics of the tunnel contact of a STM-tip and an H-terminated n-Si(111) surface have been studied under optical excitation. We have used the abrupt increase of the reverse tunnel current and its strong dependence on the light illumination of the tunnel contact to realise an optical governed point transistor. The observed dependencies of the STM tunnel contact demonstrate new possibilities for using the STM-tip-tunnel separation-semiconductor structure as an optical controlled nanosize Auger-transistor.

The current-voltage (I–V) characteristics of contacts to CdTe are studied at 300 and 77 K. The contacts were obtained by chemical deposition of Au on the (111) surface of polycrystalline p-CdTe after etching in bromine methanol and after passivation in (NH4)2Sx. It is shown that passivation of the surface noticeably linearizes the I–V characteristics at 300 K and only slightly at 77 K. The measurements of the low-temperature photoconductivity of the samples showed that the passivation of the surface in (NH4)2Sx decreases the surface-state density at the metal-semiconductor interface.

A Schottky-barrier (SB) metal/semiconductor contact (MSC) is considered. A model contact characterized by the normal distribution of the SB height and the corresponding distribution of the series resistance over the contact area is investigated numerically. A general approach to the analysis of inhomogeneous and homogeneous contacts is demonstrated. The approach is based on the concept of the nonlinear dependence of the barrier height (effective height in the case considered) on the bias voltage. An analytic approximation corresponding to the known empirical expression is obtained for the current-voltage characteristic of the contact. The model considered is applied to interpret experimental current and temperature dependences of the 1/f-noise level in SB contacts.

We investigate the $I(V)$ characteristics (current versus bias voltage) of side-gated quantum-point contacts, defined in $\mathrm{GaAs}∕{\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ heterostructures. These point contacts are operated in the closed-channel regime, that is, at fixed gate voltages below zero-bias pinch-off for conductance. Our analysis is based on a single scaling factor, extracted from the experimental $I(V)$ characteristics. For both polarities, this scaling factor transforms the change of bias voltage into a change of electron energy. The latter is determined with respect to the top of the potential barrier of the contact. Such a built-in energy-voltage calibration allows us to distinguish between the different contributions to the electron transport across the pinched-off contact due to thermal activation or quantum tunneling. The first involves the height of the barrier, and the latter also its length. In the model that we are using the channel length remains the only adjustable parameter since the barrier height can be experimentally determined. For short $(\ensuremath{\sim}0.06\phantom{\rule{0.3em}{0ex}}\mathrm{\ensuremath{\mu}}\mathrm{m})$ contacts, the $I(V)$-derived lengths agree rather well with those estimated from the geometrical layout, whereas nominally long $(\ensuremath{\sim}1.2\phantom{\rule{0.3em}{0ex}}\mathrm{\ensuremath{\mu}}\mathrm{m})$ contacts are typically found to consist of very short $(\ensuremath{\sim}0.2\phantom{\rule{0.3em}{0ex}}\mathrm{\ensuremath{\mu}}\mathrm{m})$ barriers. We have mapped the height of the barrier as a function of the gate voltage, and found that its behavior differs strongly from that extrapolated using conventional bias spectroscopy in the open-channel regime above conductance pinch-off.

A new and simple-to-use method to obtain homogeneous Schottky barrier heights from effective barrier heights and ideality factors that are determined from current-voltage (I-V) characteristics of metal-semiconductor contacts is presented. This approach is justified by a theory of metal-semiconductor interfaces with laterally inhomogeneous distributions of barrier heights. Effective barrier heights and ideality factors were determined from I-V characteristics of Si and GaN Schottky contacts and a linear reduction of the effective barrier heights with increasing ideality factors was always observed. These findings are explained by numerical simulations of inhomogeneous Schottky contacts which are based on theoretical results by Tung [Phys. Rev. B 45, 13509 (1992)]. The homogeneous barrier heights of metal-semiconductor contacts are obtained by a linear extrapolation of the effective barrier heights to nif ≅ 1.01, the value of the ideality factor characteristic for image-force lowering of Schottky barriers only.

In present study five synthesized organic semiconductor compounds have been used for fabrication of the planar metal / organic semiconductor / metal structures. Both top electrode and bottom electrode configurations were used. Current-voltage (I-V) characteristics of the samples were investigated. Effect of the hysteresis of the I-V characteristics was observed for all the investigated samples. However, strength of the hysteresis was dependent on the organic semiconductor used. Study of I-V characteristics of the top contact Al/AT-RB-1/Al structures revealed, that in (0 – 500) V voltages range average current of the samples measured in air is only slightly higher than current measured in nitrogen ambient. Deposition of the ultra-thin diamond like carbon interlayer resulted in both decrease of the hysteresis of I-V characteristics of top contact Al/AT-RB-1/Al samples. However, decreased current and decreased slope of the I-V characteristics of the samples with diamond like carbon interlayer was observed as well. I-V characteristic hysteresis effect was less pronounced in the case of the bottom contact metal/organic semiconductor/metal samples. I-V characteristics of the bottom contact samples were dependent on electrode metal used. DOI: http://dx.doi.org/10.5755/j01.ms.19.1.3816

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Effect of the asymmetry of the redox molecule (RM) coupling to the working electrodes on the Coulomb blockade and the operation of molecular transistor is considered under ambient conditions for the case of the non-adiabatic tunneling through the electrochemical contact having a one-level RM. The expressions for the tunnel current, the positions of the peaks of the tunnel current/overpotential dependencies, and their full widths at the half maximum are obtained for arbitrary values of the parameter d describing the coupling asymmetry of the tunneling contact and the effect of d on the different characteristics of the tunneling contact is studied. The tunnel current/overpotential and the differential conductance/bias voltage dependencies are calculated and interpreted. In particular, it is shown that the effect of the Coulomb blockade on the tunnel current and the differential conductance has a number of new features in the case of the large coupling asymmetry. It is also shown that, for rather large values of the solvent reorganization energy, the coupling asymmetry enhanced strongly amplification and rectification of the tunnel current in the most of the regions of the parameter space specifying the tunneling contact. The regions of the parameter space where both strong amplification and strong rectification take place are also revealed. The obtained results allow us to prove the possibility of the realization of the effective electrochemical transistor based on the one-level RM.

Surface electronic properties of GaN nanowires have been investigated using scanning probe microscopy and correlated with metal/nanowire contact characteristics. Surface current map of the nanowire was observed to be highly nonuniform, resulting from a large variation in surface barrier of the nanowire, on the order of a few tenths of an eV. The surface barrier non‐uniformity, which most likely determines the formation of an ohmic or Schottky contact, is increased dramatically with the nanowire surface deformation. Current–voltage characteristics and scanning gate microscopy of the nanowires also indicate significant carrier trapping at the nanowire and silicon dioxide surface. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Vacuum condensed Al-CdS-Al structures have been studied under unidirectional voltage pulse excitation. The current-voltage characteristics show negative resistance in the low-voltage region. The results are explained in terms of the build-up process of barrier field at the cathode owing to reapplication of the time increasing voltage, superposed on the decay of space charge in the barrier region accumulated during application of the previous voltage pulse. The voltage corresponding to the minimum in the current-voltage characteristics has been used to evaluate the lifetime of positive space charge trapped in the surface states at the metal semiconductor contact interface. This is in the range of a few milliseconds. The results depend upon the contact characteristics and are affected by the external dc biasing of the cathode barrier.

Auger electron spectroscopy (AES) is used to investigate the effect that high temperature annealing has on GaN and metal contacts to p-GaN. Current-voltage characteristics are used to determine the Schottky barrier heights and ideality factors of Pt-Au and Ni-Au contacts to p-GaN, and the effect of temperature on the contact characteristics is also examined.