Deep levels in Ga doped n-type CdMnTe of 1% and 5% Mn contents and In doped n-type CdMnTe of 20% Mn content were studied using deep level transient spectroscopy technique. Our deep level transient spectroscopy results show presence of several groups of different traps.
Jellium metal surface properties such as the surface dipole barrier and work function are obtained in the linear potential approximation to the effective potential at the surface. The metal surface position and field strength are determined respectively by the requirement of overall charge neutrality and the constraint set on the electrostatic potential by the Budd-Vannimenus theorem. The calculations are primarily analytic and these properties are given in terms of universal functions of the field strength. The results obtained employing the Ceperly-Alder expression for the correlation energy closely approximate those of Lang and Kohn.
We apply a one-dimensional model to studies of intrinsic Schottky barriers. The semiconductor possesses two bands (s and p) and the metal has one conduction band. For the first time explicitly analytic formula for the density of states is given. An extremely accurate analytic formula (compared to numerical results) for the Fermi level position is proposed. It is shown that the Fermi level of the (covalent) semiconductor-metal interface is independent of the metal bulk parameters. Also self-consistent numerical results are presented.
The new possibilities of the electrical characterization of the metal-semiconductor interface in Schottky junctions are briefly outlined and demonstrated by using an example of experimental results taken from the literature. The interface parameters obtained for GaAs Schottky junctions with different metallizations are summarized.
An (Au/Ti)/Al₂O₃/n-GaAs structure with thin (30 Å) interfacial oxide layer (Al₂O₃), formed by atomic layer deposition technique is fabricated to investigate both frequency and applied bias voltage dependences of real and imaginary parts of dielectric constant (ε' and ε'') and electric modulus (M' and M''), loss tangent tanδ and ac electrical conductivity σ_{AC} in a wide frequency range from 1000 Hz to 1 MHz at room temperature. The dielectric properties of the (Au/Ti)/Al₂O₃/n-GaAs metal-insulator-semiconductor structure are obtained using the forward and reverse bias capacitance-voltage (C-V) and conductance-voltage (G/ω-V) measurements in the applied bias voltage range from -4 V to +4 V, at room temperature. Experimental results show that the dielectric parameters were strongly frequency and voltage dependent. For each frequency the (C-V) plots show a peak and the change in frequency has effect on both the intensity and position of the peak. ε', ε'' and tanδ decrease with increasing frequency, whereas σ_{AC} increases with increasing frequency at applied bias voltage. M' increases with the increasing frequency and reaches a maximum. M'' shows a peak and peak position shifts to higher frequency with increasing applied voltage. It can be concluded that the ε', ε'', tanδ, M', M'' and σ_{AC} values of the (Au/Ti)/Al₂O₃/ n-GaAs structure are strongly dependent on both the frequency and applied bias voltage especially in the depletion and accumulation region. Also, the results can be deduced to imply that the interfacial polarization is easier at low frequencies, therefore contributing to the deviation of dielectric properties and AC electrical conductivity of (Au/Ti)/Al₂O₃/n-GaAs structure.
The frequency-dependent electrical characteristics of Au/Poly (3-Substituted thiophene) (P3DMTFT)/ n-GaAs Schottky barrier diodes have been investigated by using capacitance-voltage (C-V) and conductance-voltage (G/ω-V) measurements at room temperature. Negative capacitance behavior has been observed in the C-V characteristic for each frequency. The magnitude of absolute value of C was found to increase with decreasing frequency in the forward bias region. The value of G/ω increases with decreasing frequency in the positive region. This can be attributed to the increase in the polarization at low frequencies and to the fact that more carriers are introduced into the structures. Negative capacitance phenomenon can be explained by the loss of interface charges from the occupied states below the Fermi level, caused by impact ionization process. According to obtained result, the values of C and G/ω are strong functions of frequency and applied bias voltage, particularly in the accumulation an inversion region. Doping concentration (N_{d}), diffusion potential (V_{d}), Fermi energy level (E_{f}), and barrier height (Φ_{b}(C-V)) values have been calculated from reverse bias C^{-2}-V plots for 3 MHz. Finally, the obtained value of R_{s} in the accumulation region increases with decreasing frequency.
In this study, we investigated the electrical properties of the Au/P3HT/n-GaAs Schottky diode at room temperature by using current-voltage method. The values of ideality factor and barrier height of the diode were found to be 2.45 and 0.85 eV, respectively. n ideality factor greater than unity indicates that the diode exhibits non-ideal current-voltage behavior. This behavior results from the effect of series resistance and the presence of an interfacial layer. These values were also determined from the Cheung functions and the Norde method due to the non-ideal behavior of the diode and it was seen that there was an agreement with series resistance. Also the interface states energy distribution of the diode was determined from the forward bias I-V measurements by taking into account the bias dependence of the effective barrier height. The obtained electrical parameters of the Au/P3HT/n-GaAs Schottky diode are higher than that of the conventional Au/n-GaAs Schottky diodes.
The numerical fitting of an analytical function representing electron density profile at a jellium surface to the one tabulated by Lang and Kohn is presented. The two sets of parameters entering the electron density profile is proposed. The first one is obtained by purely numerical fitting, and the second one is calculated under condition that electron density profile must satisfy the Budd-Vannimenus theorem. The obtained parameters are given as analytical functions of the Wigner-Seitz radius r_{s} describing mean electron density n̅ in a metal (n̅^{-1} = 4/3πr³_{s} ). The comparison of presented electron density profile with variational trial function given by Perdew is also discussed.
This work shows that cytosine biomolecules can control the electrical characteristics of conventional Cu/n-InP metal-semiconductor contacts. A new Cu/n-InP Schottky junction with cytosine interlayer has been formed by using a drop cast process. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics of Cu/cytosine/n-InP structure were investigated at room temperature. A potential barrier height as high as 0.68 eV has been achieved for Cu/cytosine/n-InP Schottky diodes, which have good I-V characteristics. This good performance is attributed to the effect of interfacial biofilm between Cu and n-InP. By using C-V measurement of the Cu/cytosine/n-InP Schottky diode the diffusion potential and the barrier height have been calculated as a function of frequency. Also, the interface-state density of the Cu/cytosine/n-InP diode was found to vary from 2.24×10^{13} eV^{-1} cm^{-2} to 5.56×10^{12} eV^{-1} cm^{-2}.
It is shown theoretically that, in contradiction to massive specimens, the work function of ferromagnetic thin films does not depend linearly on the square of magnetization as a consequence of the inhomogeneous magnetization distribution. This theoretical conclusion is confirmed by experimental investigations of gadolinium films as well as interpretation of the results reported for nickel samples.
Positron affinities and deformation potentials are calculated in cubic bulk semiconductors using the density functional theory with the electron and positron energies in the local density approximation and generalized gradient approximation, respectively. In order to estimate these quantities, two different forms of the electron-positron correlation potential are used. Positron affinities calculated using these two correlation potentials differ by about 0.3 eV. Our calculated affinities in 3C-SiC are in better agreement with experiments than those obtained previously by another first principles method. In the present work the positron affinity in BN is found to be quite close to the one in diamond.
We report the results of our studies of ruthenium layer structures adsorbed on GaN(0001). Ruthenium was evaporated at room temperature under ultrahigh vacuum conditions onto n-type GaN substrates epitaxially grown on sapphire. While X-ray photoelectron spectroscopy confirmed the presence of Ru bonds in the deposited adlayers, the ultraviolet photoelectron spectroscopy show a peak at the Fermi level as well as lines originating from ruthenium. The height of the Schottky barrier was calculated based on the data measured by X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy and amounts to 1.5 eV.
The electronic structure of n-type GaN(0001) surface and its modification by N⁺ ion bombardment are presented in this report. The studies were carried out in situ in ultrahigh vacuum by ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, and low-energy electron diffraction. Low-energy N⁺ ion bombardment, which was done using an ion gun at an energy of 200 eV, leads to nitriding of the surface. The process changes the surface stoichiometry and, consequently, provides formation of a disordered altered GaN layer. The calculated electron affinity of the clean n-GaN surface of 3.4 eV and band bending of 0.2 eV became changed after bombardment to 2.9 eV and 0.8 eV, respectively. The obtained difference in valence band maximum between the clean sample and the bombarded one was 0.6 eV.
The aim of this paper is to summarize the results of experiments carried out at our laboratory on the response of the work function of several thin films of transition metals and rare earth metals to interaction with molecular hydrogen. The main focus concerns the description of surface phenomena accompanying the reaction of hydride formation as a result of the adsorbate's incorporation into the bulk of the thin films. Work function changes Δ Φp caused by adsorption and reaction concern the surface, hence this experimental method is appropriate for solving the aforementioned problem. A differentiation is made between the work function changes ΔΦp due to creation of specific adsorption states characteristic of hydrides, and ΔΦp arising as a result of surface defects and protrusions induced in the course of the reaction. The topography of thin metal films and thin hydride films with defects and protrusions was illustrated by means of atomic force microscopy. For comparison, the paper discusses work function changes caused by H_2 interaction with thin films of metals which do not form hydrides (for example platinum), or when this interaction is performed under conditions excluding hydride formation for thermodynamic reasons. Almost complete diminishing of ΔΦp was observed, in spite of significant hydrogen uptake on some rare earth metals, caused by formation of the ordered H-Y-H surface phase.
The dynamics of the depletion field screening induced by photoexcited carriers and THz generation caused by the electric-field-induced optical rectification are simulated for GaAs surface excited by femtosecond laser radiation on the basis of an ensemble Monte Carlo method. The results show that the photocarrier-induced screening occurs on a subpicosecond time scale and THz pulse essentially changes its wave form depending on excitation pulse duration and fluence. The possibility to use the depletion electric field induced THz generation for study of subpicosecond electric field screening dynamics is discussed.
The influence of hydrostatic pressure up to 8 kbar on the barrier height of epitaxially MBE-grown Al on AlGaAs metal-semiconductor junctions is reported. The pressure change of the Schottky barrier on n-type AlGaAs is the same as that of the energy gap (for both direct and indirect-gap AlGaAs compositions), while for p-type AlGaAs it is negligible. This result is in direct conflict with a class of models of the Schottky barrier formation based on a concept of a semiconductor neutrality level alignment with the metal Fermi level.
The adsorption and coadsorption of beryllium and potassium on the tungsten (001) plane was studied using a probe-hole field electron microscope (FEM). Measurements were made at 78 K for potassium and at 300 K for beryllium. It has been found that the adsorption of potassium decreases and that of beryllium increases the work function of the W(001) plane. At small coverages with potassium atoms (θ_{k} < 0.2) on the W(001) plane successive evaporation of beryllium atoms causes a decrease of the work function. At larger coverages with potassium atoms an opposite effect is observed. An attempt has been made to compare the experimental results with the theoretical models suggested recently.
We present a solution-gated in situ Raman spectroscopy approach, which enables the electrical characterization of graphene on a copper substrate without the need of a transfer process. The application of a voltage across the solution resulted in a shift of the Raman G-band without a significant shift of the 2D band. This observation allowed for the separation of the effects of strain and doping. Based on the G and 2D band shifts we show that we can manipulate the n-type carrier concentration of graphene directly on the copper substrate in a range from about 8× 10¹² cm¯² to about 1.5× 10¹³ cm¯².
We report on attempts to produce a graphene based liquid flow sensor. Our results indicate that modifications of the electric double layer, formed in the vicinity of the graphene surface, dominate over mechanisms responsible for liquid flow-induced voltage/current generation. Several graphene structures were tested in different measurement configurations, aimed to maximize the generated signal amplitude and its stability. Some realizations of working devices in water as well as in aqueous solutions of NaCl or HCl are presented.
Taking into account the available experimental results, we model the electronic properties and current-voltage characteristics of a ferromagnet-semiconductor junction. The Fe/GaAs interface is considered as a Fe/(i-GaAs)/n⁺-GaAs/n-GaAs multilayer structure with the Schottky barrier. We also calculate numerically the current-voltage characteristics of a double-Schottky-barrier structure Fe/GaAs/Fe, which are in agreement with available experimental data. For this structure, we have estimated the spin current in the GaAs layer, which characterizes spin injection from the ferromagnet to the semiconductor.
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