A. Sellai

Barrier inhomogeneities of tungsten Schottky diodes on 4H-SiC

Electrical properties of tungsten on silicon carbide (4H-SiC) Schottky diodes are investigated through the analysis of the forward current–voltage (I–V) characteristics measured at elevated temperatures within the range of 303–448 K. The subsequently derived Schottky barrier heights (SBHs) and ideality factors are found to be temperature dependent with distributions that are adequately explained within the framework of the model proposed by Tung in which he considers the barrier at a metal–semiconductor interface as consisting of locally non-uniform but interacting patches of different barrier heights embedded in a background of uniform barrier height. A uniform barrier height of 1.248 eV, a Richardsons constant of 129.95 A cm−2 K2 and a factor To of 23.92 K obtained agree very well with values published previously for similar Schottky barrier systems. Therefore, it has been concluded that the temperature-dependent I–V characteristics of the device can be successfully explained with lateral inhomogeneities distribution of the SBH.

Electrical characteristics of Mo/4H-SiC Schottky diodes having ion-implanted guard rings: temperature and implant-dose dependence

The electrical characteristics of ion-implanted guard rings for molybdenum (Mo) Schottky diodes on 4H-SiC are analyzed on the basis of the standard thermionic emission model and the assumption of a Gaussian distribution of the barrier height. For edge termination, high-resistivity guard rings manufactured by carbon and aluminum ion-implanted areas were used. Extractions of barrier heights of molybdenum on silicon carbide (4H-SiC) Schottky diodes have been performed on structures with various gate metallization, using both current–voltage–temperature (I–V–T) and capacitance–voltage (C–V) measurements. Characteristic features of the Schottky barrier height (SBH) are considered in relation to the specific dose of the carbon- or aluminum-implanted guard ring. Contacts showed excellent Schottky behavior ideality factors between 1.02 and 1.24 in the range of 303–473 K. The measured SBHs were between 0.92 and 1.17 eV in the same temperature range from I–V–T characteristics. The variations in the barrier height, which is significantly temperature- and implantation-dose-dependent, are well fitted to a single Gaussian distribution function. Experimental results agree reasonably well by using this approach, particularly for carbon implantation dose of 1.75 × 1014 cm−2, and a mean barrier height () of 1.22 eV and zero bias standard deviation σ0 = 0.067 V have been obtained. Furthermore, the modified Richardson plot according to the Gaussian distribution model resulted in a mean barrier height () and a Richardson constant (A*) of 1.22 eV and 148 A cm−2 K−2, respectively. The A* value obtained from this plot is in very close agreement with the theoretical value of 146 A cm−2 K−2 for n-type 4H-SiC. Therefore, it has been concluded that the temperature dependence of the forward (I–V) characteristics of the Mo/4H-SiC contacts can be successfully explained on the basis of a thermionic emission conduction mechanism with Guassianly distributed barriers.

Quantum efficiency in GaAs Schottky photodetectors with enhancement due to surface plasmon excitations

Abstract The overall quantum efficiency in surface plasmon (SP) enhanced Schottky barrier photodetectors is examined by considering both the external and internal yield. The external yield is considered through calculations of absorption and transmission of light in a configuration that allows reflectance minimization due to SP excitation. Following a Monte Carlo method, a procedure is presented to estimate the internal yield while taking into account the effect of elastic and inelastic scattering processes on excited carriers subsequent to photon absorption. The relative importance of internal photoemission and band-to-band contributions to the internal yield is highlighted along with the variation of the yield as a function of wavelength, metal thickness and other salient parameters of the detector.

Barrier height and interface characteristics of Au/Mn5Ge3/Ge (1?1?1) Schottky contacts for spin injection

The interface states in Au/Mn5Ge3/Ge Schottky barrier diodes prepared for spintronic applications are investigated using dc I-V-T as well as ac admittance measurements. The latter were performed under forward and reverse biases over a wide range of frequencies (1 kHz?3 MHz) while varying the temperature from 50 to 300 K. Variations of the ideality factor with temperature are related to the density of interface states, the presence of which is also evidenced as an excess capacitance in the capacitance?frequency characteristics as well as a peak in the conductance versus frequency. The temperature dependence of these interface state densities, determined to be of the range 1013?1014?eV?1?cm?2, and their energy distribution with respect to the bottom of the conduction band are examined.

Deep-level transient spectroscopy of interfacial states in “buffer-free” p-i-n GaSb/GaAs devices

A systematic study was carried out on defect states in Interfacial Misfit (IMF) unpassivated and Te-passivated IMF in p-i-n GaSb/GaAs devices using Deep Level Transient Spectroscopy (DLTS) and Laplace DLTS. Additionally, Current-Voltage (I–V) measurements were performed, which showed that the turn-on voltage (Von) of passivated samples is lower than that for unpassivated samples; an effect which can be explained by the introduction of new defects states near to the interface of GaSb/GaAs, where Te was incorporated to passivate the IMF. The Capacitance-Voltage (C-V) analysis demonstrates that these new states are the consequence of adding Te at the misfit of GaSb/GaAs. Furthermore, DLTS measurements reveal a distribution of states including a main midgap energy level, namely the well documented EL2 trap, with some peculiar behaviour. Most of these levels are related to interface states that are generated by the mismatch between GaAs and GaSb. Originally, the addition of Te atoms was thought to passivate these interface states. On the contrary, this paper, which attempts at correlating the current-voltage and capacitance-voltage characteristics to the DLTS results, shows clearly that Te atoms increase the density of interface states.

Self-organization of gold nanoparticles on silanated surfaces

Summary The self-organization of monolayer gold nanoparticles (AuNPs) on 3-aminopropyltriethoxysilane (APTES)-functionalized glass substrate is reported. The orientation of APTES molecules on glass substrates plays an important role in the interaction between AuNPs and APTES molecules on the glass substrates. Different orientations of APTES affect the self-organization of AuNps on APTES-functionalized glass substrates. The as grown monolayers and films annealed in ultrahigh vacuum and air (600 °C) were studied by water contact angle measurements, atomic force microscopy, X-ray photoelectron spectroscopy, UV–visible spectroscopy and ultraviolet photoelectron spectroscopy. Results of this study are fundamentally important and also can be applied for designing and modelling of surface plasmon resonance based sensor applications.

Resonant tunneling diode circuits using Pspice

The measured I – V data and the large-signal equivalent circuit of a resonant tunneling diode are exploited, through the analog behavioral modeling capabilities of Pspice, to create a Pspice compatible model for the diode. The model is used, with very few other components, in the simulation of a number of circuit applications including a sinusoidal wave generator, a frequency multiplier and three state logic circuits. The simulated circuit details, the related waveforms and three-state logic operations are described. The circuits are characterized mainly by their reduced complexity and ease of analysis. q 2003 Elsevier Science Ltd. All rights reserved.

Electrical characteristics of InAs self-assembled quantum dots embedded in GaAs using admittance spectroscopy

GaAs based structures in which are embedded InAs self-assembled quantum dots are studied using admittance measurements taken over a large frequency spectrum and for several temperatures. The presence of quantum dots is evidenced in the capacitance-voltage characteristics by one, or more, plateau-like structures related to the processes of charging and discharging of the quantum dots. Concurrently, the measured conductance exhibits a peak in a certain bias range that coincides with the plateau-like structure in the capacitance but only for temperatures below 150 K. The conductance dependence on both the temperature and applied bias is attributed to two mechanisms of carrier escape/capture mechanisms from the InAs embedded quantum dots into/out of the hosting GaAs; a thermally activated process for temperatures above 80 K and a perceptibly nonthermal tunneling process for temperatures below 40 K. The conductance data is used to estimate rates and activation energies in association with the electron escape mechanisms from the quantum dots.

Features of a tunnel diode oscillator at different temperatures

Current-voltage measurements were performed on a tunnel diode (TD) and the basic features of the I-V characteristics were analyzed in the temperature range 100-300K. Based on these characteristics, a TD-based oscillator is designed and simulated using circuit analysis software (PSpice). It is shown, in particular, that the amplitude and the frequency of the obtained sinusoidal waveforms can be practically temperature independent provided that the diode is adequately biased in its negative conductance region.

DENSITY OF SURFACE STATES IN Pd/SiGe/Si INTERFACE FROM CAPACITANCE MEASUREMENTS

Pd/Si0.9Ge0.1/Si Schottky barrier diodes subjected to irradiation are characterized using capacitance and conductance measurements performed under forward and reverse bias while varying the temperature and frequency. The C–V technique has been used in particular to determine the carriers profile as well as the interface state density and its energy distribution.