Forward Current Transport Research Articles

Non-Monotonic $\gamma$-Ray Influence on Mo/n-Si Schottky Barrier Structure Properties

The current-voltage characteristics of Mo/n-Si Schottky barrier structure irradiated by γ-rays of 60Co were investigated in the temperature range of 120-330 K. The zero-bias barrier height, ideality factor, and reverse current were found to depend non-monotonously on the cumulative dose. The samples exposed to different radiation doses were found to display different forward current transport mechanism. In non-irradiated structure the current-transport mechanism is thermionic emission (TE) over inhomogeneous barrier. In the structure exposed to 10 kGy the mechanism is defect-assisted tunneling in the lower temperature range 120-220 K, and TE over inhomogeneous barrier in the higher temperature range 260-330 K. In the structure exposed to 100 kGy the mechanism is tunneling in the 150-220 K range, and TE (dominant) and tunneling at 260-330 K. The obtained results are explained by the increase of radiation defect concentrations (for comparatively small doses), and by further gettering of defects in the inhomogeneous regions as the irradiation dose increases.

An analysis of the effect of illumination to the reverse and forward bias current transport mechanisms in an efficient n-ZnO/n-CdS/p-Cu(In,Ga)Se2 solar cell

Temperature dependent current–voltage measurements are used to determine the effect of white light illumination on the dominant current transport mechanism in an efficient n-ZnO/n-CdS/p-Cu(In,Ga)Se2 heterojunction solar cell. The forward J–V characteristics are modelled by double exponential expression. In the dark, the forward current transport is mainly dominated by recombination at interfacial regions with pronounced tunnelling effect. Nevertheless, approximately above 200K, the thermal dependence of the diode parameters in the second junction interface can be explained in terms of properly increasing contribution of pure depletion region recombination mechanism. Under white light illumination, the forward current is still dominated by the tunnelling enhanced interface recombination mechanism with considerably enhanced tunnelling contribution. The presence of a significant distortion observed below 180K is attributed to the shift of Fermi level at junction interface and recharge distribution in the junction region due to metastable nature of the defect states. Below and above than 230K, the reverse bias current transport in the dark is described by using space charge limited current and a thermally activated behaviour, respectively. Under illumination the variation of temperature dependent reverse current with voltage suggests that either the SCL current in the velocity saturation regime or tunnelling dominates the current transport.

Forward Current Transport Mechanism and Schottky Barrier Characteristics of a Ni/Au Contact on n-GaN

The forward current transport mechanism and Schottky barrier characteristics of a Ni/Au contact on n-GaN are studied by using temperature-dependent current-voltage (T—I—V) and capacitance-voltage (C—V) measurements. The low-forward-bias I-V curve of the Schottky junction is found to be dominated by trap-assisted tunneling below 400 K, and thus can not be used to deduce the Schottky barrier height (SBH) based on the thermionic emission (TE) model. On the other hand, TE transport mechanism dominates the high-forward-bias region and a modified I—V method is adopted to deduce the effective barrier height. It is found that the estimated SBH (∼0.95 eV at 300K) by the I—V method is ∼0.20 eV lower than that obtained by the C—V method, which is explained by a barrier inhomogeneity model over the Schottky contact area.

Temperature-dependent forward gate current transport in atomic-layer-deposited Al2O3/AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor

The mechanisms of the temperature-dependent forward gate current transport in the atomic-layer-deposited Al2O3/AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor (MISHEMT) were investigated. In contrast to the conventional Schottky-gate AlGaN/GaN HEMT, thermionic field emission was found not to be the dominant transport mechanism for the Al2O3/AlGaN/GaN MISHEMT. Fowler–Nordheim tunneling was found to be dominant at low temperature (T<0 °C) and high electrical filed, whereas trap assistant tunneling was found to be dominant at medium electrical field and high temperature (T>0 °C).

Mechanism of forward current transport in modified-surface Au-CdTe photodiodes

Current-voltage characteristics of surface-barrier diodes based on n-CdTe substrates treated in aqueous solutions of alkali metal salts were studied. It was found that the forward current is controlled by recombination processes in the space-charge region and the above-barrier carrier transport.

Electrical and piezoresistive properties of ion beam deposited DLC films

In present study diamond like carbon (DLC) films were deposited by closed drift ion source from the acetylene gas. The electrical and piezoresistive properties of ion beam synthesized DLC films were investigated. Diode-like current–voltage characteristics were observed both for DLC/nSi and DLC/pSi heterostructures. This fact was explained by high density of the irradiation-induced defects at the DLC/Si interface. Ohmic conductivity was observed for DLC/nSi heterostructure and metal/DLC/metal structure at low electric fields. At higher electric fields forward current transport was explained by Schottky emission and Poole–Frenkel emission for the DLC/nSi heterostructures and by Schottky emission and/or space charge limited currents for the DLC/pSi heterostructures. Strong dependence of the diamond like carbon film resistivity on temperature has been observed. Variable range hopping current transport mechanism at low electric field was revealed. Diamond like carbon piezoresistive elements with a gauge factor in 12–19 range were fabricated.

Effect of doping on the forward current-transport mechanisms in a metal–insulator–semiconductor contact to InP:Zn grown by metal organic vapor phase epitaxy

A detailed study of the effect of doping density on current transport was undertaken in Au metal–insulator–semiconductor (MIS) contacts fabricated on Zn-doped InP layers grown by metal organic vapor phase epitaxy. A recently developed method was used for the simultaneous analysis of the current–voltage ( I– V) and capacitance–voltage ( C– V) characteristics in an epitaxial MIS diode which brings out the contributions of different current-transport mechanisms to the total current. I– V and high-frequency C– V measurements were performed on two MIS diodes at different temperatures in the range 220–395 K. The barrier height at zero bias of Au/InP:Zn MIS diodes, φ 0 (1.06 V±10%), was independent both of the Zn-doping density and of the surface preparation. The interface state density distribution N ss as well as the thickness of the oxide layer (2.2±15% nm) unintentionally grown before Au deposition were independent of the Zn-doping concentration in the range 10 16< N A<10 17 cm −3; not so the effective potential barrier χ of the insulator layer and the density of the mid-gap traps. χ was much lower for the highly-doped sample. Our results indicate that at high temperatures, independent of the Zn-doping concentration, the interfacial layer-thermionic (ITE) and interfacial layer-diffusion (ID) mechanisms compete with each other to control the current transport. At intermediate temperatures, however, ITE and ID will no longer be the only dominant mechanisms in the MIS diode fabricated on the highly-doped sample. In this case, the assumption of a generation–recombination current permits a better fit to the experimental data. Analysis of the data suggests that the generation–recombination current, observed only in the highly-doped sample, is associated with an increase in the Zn-doping density. From the forward I– V data for this diode we obtained the energy level (0.60 eV from the conduction band) for the most effective recombination centers.

A self-consistent technique for the analysis of the temperature dependence of current–voltage and capacitance–voltage characteristics of a tunnel metal-insulator-semiconductor structure

A new formalism is reported for the analysis of the current–voltage (I–V) characteristics of a tunnel metal-insulator-semiconductor (MIS) device, which considers a bias dependent distribution of interface states and barrier lowering due to the image force. Our theoretical expression for the I–V characteristics is general in the sense that it is applicable even under conditions when both the thermionic emission and the diffusion mechanisms of current transport compete with each other. The method is ideal for new epitaxial materials and devices where the carrier density is not known precisely beforehand. A self-consistent method of analysis is reported to determine the characteristic parameters of MIS diodes, using simultaneously the I–V and capacitance–voltage data as a function of temperature. This computational analysis has been used to examine the current transport mechanism in an Au/p-InP epitaxial MIS diode. The experimental verification of the theory and computational analysis is done by comparing the values of the interface state density distribution in thermal equilibrium with the semiconductor Nss, obtained from the forward I–V characteristics, with those directly measured by the multifrequency admittance method. Excellent agreement from these comparisons strongly supports the validity of the theory. Over the temperature range of 200–393 K, our results indicate that the interfacial layer-thermionic emission was clearly the dominant mechanism of the forward current transport in an MIS fabricated on a lightly doped InP:Zn epitaxial layer. The transmission coefficient through the insulator layer obtained from the reverse I–V characteristics was θp=1.43×10−3±7% from which we estimate an oxide thickness of 2.2 nm. The analysis of the barrier height φb0 versus temperature, obtained from 1 MHz C–V data provided a value φ0=1.06 V±10% for the zero bias and zero temperature barrier height.

The barrier height and interface effect of Au-n-GaN Schottky diode

Schottky barrier contact using Au and ohmic contact using Al were made on n-GaN grown by hydride vapour phase epitaxy. The diodes were characterized in the range 77-373 K. Under forward bias, the ideality parameter n=1.04 and the threshold voltage is 1.1 V. The reverse bias leak current is below 10-9 A on a reverse bias of -10 V. The temperature-dependence of the I-V characteristics shows two regimes of forward current transport: one at low voltage governed by thermionic emission and the high-voltage regime due to spatial inhomogeneities at the metal-semiconductor interface. The barrier height phi B and the electron affinity XS were determined to be 0.91 and 4.19 eV, respectively, by I-V measurement; and 1.01+or-0.02 and 4.09 eV, respectively, by C-V measurement. The results have been discussed.

A New Method for the Simultaneous Analysis of I-V/T and C-V/T Measurements of an Au/P-Inp Epitaxial Schottky Diode

ABSTRACTWe have developed a new approach to analyze the current- voltage (I-V) characteristics of a tunnel metal-interface layer - semiconductor (MIS) diode which takes into account the voltage dependence of interface states distribution (Nss) and the barrier lowering due to image force. Our method of analysis uses simultaneously the I-V/T and C-V/T data to determine the characteristic parameters of an MIS diodes and is ideal for new epitaxial materials and devices where the carrier density is not known precisely before hand. The experimental verification of our approach to analyze the nonideal I-V/T and C-V/T characteristics of MIS diodes was done by comparing the values of Nss extracted from the room temperature forward I-V characteristics of a p-InP/Au MIS diodes with those obtained by the multi-frequency admittance method. Excellent agreement between the values of Nss determined by two different techniques strongly support the validity of our theoretical expression for the I-V/T characteristics and the method of analysis. Our results indicate that the interface layer thermionic emission was clearly the dominant mechanism of the forward current transport in epitaxial Au/p-InP MIS diodes over the temperature range 200–393 K. The transmission coefficient of the interface-layer obtained from the reverse I-V characteristics has a value of 1.43×10−3 (±7%).

Temperature dependence of the electrical characteristics of Yb/p-InP tunnel metal-insulator-semiconductor junctions

High barrier Yb/p-InP metal-insulator-semiconductor (MIS) and metal-semiconductor (MS) junctions were fabricated by evaporation of Yb on InP:Zn substrates. The capacitance-voltage (C-V) and current-voltage (I-V) characteristics of these devices were measured over a wide range of temperatures. From the room-temperature forward I-V data, the values of 1.06 and 1.30 for the ideality factor (n) were obtained for the MIS and MS diodes, respectively. The higher value of n was attributed to an order of magnitude higher density of interface states in the MS junction than in the MIS diodes. The I-V/T data over the temperature range 190–400 K, indicated that the forward current transport in the Yb/p-InP MIS junction was controlled by the thermionic-field emission (TFE) mechanism. The analysis of the reverse saturation current I0 in terms of the TFE model provided a value of 1.07±0.03 V for the zero bias, zero temperature barrier height (φ0) which was in close agreement with the value of φ0=1.03±0.04 V, provided by the C-V data. For the MS diode, the temperature dependence of the forward I-V characteristics over the temperature range 250–350 K were well described by the thermionic emission process. However, the value of φ0=0.80±0.04 V, determined from the I-V data was much smaller than the value of φ0=0.96±0.04 V, obtained from the C-V data.

Electrical and photovoltaic characterization of nCdS:In/Si heterojunction devices

A variety of CdS/Si heterojunction solar cells have been prepared by the vacuum evaporation of indium-doped CdS films onto single-crystal p-Si substrates. Electrical and photovoltaic properties have been studied together with the influence of the back-surface field and the post-annealing process on the efficiency. Dark measurements of the voltage and of the temperature dependence of the current and the capacitance indicate that the forward current transport is predominantly characterized by a multistep tunnelling-recombination mechanism with a temperature-dependent built-in potential which decreases with increasing temperature. The validity of such a current conduction mechanism has been tested with further measurements performed under illumination.