Electrical properties of metal-oxide semiconductor nano-particle device

We have studied the electrical transport properties of two types of devices utilizing metal-oxide semiconductor nano-particles, Cu₂O and Fe₂O₃. The metal-oxide nano-particles are embedded in a polyimide matrix through chemical reaction between the metal thin film and polyamic acid as a precursor of polyimide. To test the electron tunneling via nano-particles, Au nano-electrodes are fabricated on a SiO₂/Si substrate with a 30 nm gap by electron-beam lithography. A single electron tunneling behavior was apparent in the devices with Cu₂O nano-particle inserted into the nano-gap electrodes. Also, a memory effect was measured in a floating-gated memory device structure with Fe₂O₃ nano-particles embedded in a polyimide matrix.     

Nano-scale properties of defects in compound semiconductor surfaces

The present work reviews atomic-scale properties of point defects and dopant atoms exposed on and in cleavage surfaces of III–V and II–VI semiconductors. In particular, we concentrate on the identification of the types of defects and dopant atoms, the determination of the localized defect states, the electrical charge, and lattice relaxation, as well as the measurement of the interactions between different defects and/or dopant atoms. The physical mechanisms governing the formation of defect complexes, the compensation of dopant atoms, the pinning of the Fermi level, and the stability of defects are discussed in the light of the available theoretical information and experimental results obtained mostly by scanning tunneling microscopy.     

Electrical properties of metal-piezoelectric semiconductor interface under stress

The effects of the mechanical stress on the current-voltage characteristics of metal-piezoelectric semiconductor interface are investigated for both AuCdS and AuGaP Schottky diodes. The changes in currents due to the approximately uniaxial stress, which is applied by bending the crystal wafers attached to the cantilever, are measured. Under the compressive stress parallel to the interface, the current of the diode fabricated on the (0001)Cd or that on the $\text{(}\text{1}\text{?}\text{1}\text{?}\text{1}\text{?}\text{)P}$ surface increases but that of the diode on the $\text{(000}\text{1}\text{?}\text{)S}$ or on the (111)Ga surface decreases. The direction of the changes in current is opposite under the tensile stress. The relative current change $\text{ΔI}\text{I}{}_0$ is proportional to the applied stress and its magnitude at the surface strain 3 × 10^?4is 2.4 × 10^?2, 8.0 × 10^?2, 1.0 × 10^?2 and $\text{0.5 × 10}{}^{\mathrm{?2}}\text{for diodes made on (0001)Cd, (000}\text{1}\text{?}\text{)S, (111)Ga}$ and $\text{(}\text{1}\text{?}\text{1}\text{?}\text{1}\text{?}\text{)P}$ surfaces respectively. These values are also nearly constant over the small bias region in which I₀ is proportional to exp($\text{eV}{}_{\mathrm{a}}\text{KT}$). In this region, the changes in current are transformed to the changes in barrier height. In order to explain this effect, the changes in barrier height are calculated according to the piezoelectricity in the depletion layer of the Schottky diodes. The predicted value agrees with the one obtained experimentally.     

Electronic and structural properties of hydrogen on semiconductor surfaces

In this paper we will review the scientific literature which addresses the atomic geometry and electronic structure of clean and hydrogenated semiconductor surfaces. In particular, results related to vibrational studies will be presented. First, surfaces of elemental semiconductors (Ge, Si), Ge/Si-alloys, and III–V compound semiconductors chemisorb in a first stage atomic hydrogen by saturating surface atom dangling bonds. In a second step surface bonds are broken and a change of the geometrical structure results. Finally, higher hydrogen exposures are able to etch semiconductor surfaces. Best understood to date are surfaces of Si(1 0 0), Si(1 1 1), Ge_xSi_1−x(1 0 0), and III–V's after cleavage which have been modeled by dimerized and undimerized structures. (1 0 0) surfaces of III–V semiconductors, like GaAs and InP, tend to be dimerized, too.     

Electronic and structural properties of steps on cleaved semiconductor surfaces

The work function of clean, cleaved p-Si(111) surfaces was measured in dependence of the density of cleavage steps. The contact potential difference CPD was observed first to increase then to decrease linearly with increasing step density. This dependence is caused by an increase in band bending, which saturates at a density of approximately 1 × 10⁶ steps per cm, and a decrease of the surface dipole which is proportional to the density of steps. Since the 2 × 1 reconstruction of the cleaved Si surface is ionic and buckled it increases the surface dipole moment compared with the 1 × 1 structure. Thus, a decrease of the surface dipole may be caused by removal of the 2 × 1 reconstruction on part of the step terraces. The experimental data give a width of about 28 Å for the unreconstructed stripe along the step edge.     

Electrical and photo-electrical properties of a chalcopyrite semiconductor AgInSe2

In this paper we report the electrical and photoelectrical properties of AgInSe₂. Nyquist plots for AgInSe₂, obtained at different temperatures, are perfect arcs of a semicircle with their centres lying below the abscissa at an angleα. Finite values ofα (the distribution parameter) clearly indicate a multirelaxation behaviour. Transient and steady state photoconductivity of AgInSe₂ has been studied at different temperatures and illumination levels. The lnI _ph vs lnF curves at different temperatures follow the empirical relation:I _ph ∝F ^γ. Values of γ are close to 0.5 at all the temperatures, suggesting a bimolecular recombination. Decay of the photocurrent, when the illumination is switched off, shows that during decay, photocurrent has two components, i.e. a fast decay in the beginning and a slow decay thereafter. Decay time constant for slow decay process decreases with increasing temperature, suggesting that recombination is a thermally activated process in the temperature range studied.     

Theory of semiconductor surfaces

Three kinds of recent theories of the atomic and electronic structure of semiconductor surfaces are relevant to experiment. Self-consistent calculations have provided a firm basis for understanding covalent bonding at the surface. Realistic tight-binding models can study larger unit cells which commonly occur on reconstructed surfaces. Thermochernical analysis explains the atomic arrangements obtained by annealing clean covalent surfaces.     

Electrical properties of narrow gap semiconductor PtSb2

Results of measurements of conductivity, Hall and Seebeck coefficients of tellurium doped n-type crystals of platinum antimonide are presented. The Hall coefficient and the Seebeck coefficient undergo sign inversion twice, below and above room temperature. The detailed analysis of the experimental results revealed that below 200 K PtSb₂ can be described by a simple conduction and valence band model. The energy gap E_g = (110?0.15 × T) (meV), the electron conductivity mass m_n^c/m₀ = 0.35, acoustic phonon limited electron mobility 〈μ_a〉_n = 3 × 10⁶ T^{?$\text{3}\text{2}$} ($\text{cm}{}^2\text{V · s}$) and mobility ratio 〈μ_a〉_n/〈μ_a〉_p = 0.4 are determined. However, at higher temperatures a more complicated valence band model is needed to account for the experimental results. The arguments for the existence of subsidiary valleys in the valence band are presented.     

Electrical properties of the AgTlSe2 semiconductor in the liquid state

The electrical conductivity and thermoelectric power of AgTlSe₂ have been investigated as a function of temperature from 390° C up to 590° C. The experimental data are analyzed in terms of a model developed for the density of states and electrical transport in solid amorphous semiconductors [12]. Positive thermoelectric power suggests a large predominance of holes in electrical conduction. It appears that the conduction is due to holes in localized states near the band edge.     

Electrical and optical properties of colloidal semiconductor nanocrystals in aqueous environments

Microscale and larger semiconductor crystals have electronic and optical properties that depend on their bulk band structures. When these crystals are reduced into the nanoscale, they enter a new regime in which the electrical and optical properties are no longer influenced solely by their bulk band structures, but are influenced by the crystallite size and shape. In this paper, dimensional confinement and proximity phenomena are examined for colloidal semiconductor nanocrystals in several cases of practical importance. Specifically, we determine the effective binding potentials of selected quantum dots in aqueous environments in various colloidal semiconductor nanocrystals and correlate them with experimentally obtained absorption spectra. We also study fluorescence resonance energy transfer (FRET) between semiconductor crystals connected by short peptide chains as well as the shift in photoluminescence spectra of CdTe nanowires made from a chain of CdTe quantum dots.     

Combined photoreflectance/photoluminescence studies of the electronic properties of semiconductor surfaces

A technique involving combined photoreflectance/photoluminescence measurements is proposed to study the electronic properties of semiconductor surfaces. The efficiency of the technique is illustrated by a study of the growth and degradation of the luminescence signal from selenium-passivated GaAs substrates under CW laser excitation.     

Electrical characterisation of local electronic properties of self-assembled semiconductor nanostructures using AFM

Scanning capacitance microscopy (SCM) and Kelvin probe force microscopy (KPFM) have been used to characterise self-assembled Ge nanoislands embedded in silicon. High contrast in capacitance and in surface potential are found between areas with nanostructures and areas without any nanostructures. The local dC/dV spectroscopy shows flat band voltage shift attributed to the presence of electric charges in the nanostructures. The KPFM contrast has been correlated with the band structure offsets between the nanostructure and the matrix barrier. Effects of the charging have been measured from the dC/dV curve and discussed in terms of the wetting layer influence that contributes to the escape of the charges when percolation of charges is observed.     

Microscopic structure of semiconductor surfaces

To study the initial reaction steps of hydrogen, oxygen, and water, on differently prepared single crystal surfaces of silicon, germanium/silicon alloys, indium phosphide and gallium arsenide, we used high-resolution electron energy-loss spectroscopy (HREELS) in combination with low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). Very recently, we started a program on the hydrogenation of III–V compound semiconductors, and on the oxidation of Si and III–V compound semiconductors, using alkali metals as a catalyst. This paper summarizes the present stage of our investigations, describing in particular aspects of the microscopic structure of differently prepared semiconductor surfaces.     

Electronic structure of semiconductor surfaces

Our present understanding of the electronic structure of semiconductor surfaces is reviewed. It is shown that photoemission and inverse photoemission are ideal techniques for probing occupied and unoccupied electronic states, respectively. All quantum numbers of an electron can be determined, i.e., energy, momentum, spin and angular symmetries. For simple systems, such as clean ordered surfaces with a small unit cell it is possible to understand the electronic structure from first-principles calculations. For complex systems, such as encountered during oxidation and dry etching one is restricted to measuring the properties determined by short-range order. Core level spectroscopy with synchrotron radiation is able to determine the oxidation state and the local bonding of surface and interface atoms.     

On the correlation of geometrical structure and electronic properties at clean semiconductor surfaces

In their LEED patterns most clean semiconductor surfaces show extra spots in addition to the normal beams as expected for a continuation of the bulk lattice up to the topmost layer. This means, that these surfaces are reconstructed. The (111) surfaces of silicon and germanium crystals exhibit another interesting feature: the cleaved surfaces show a metastable superstructure which irreversibly converts to a new modification upon heat treatments above about $\text{1}\text{3}$ of the melting temperatures. The structural changes are correlated with changes in the electronic properties of the surfaces. This has been shown by investigations of surface conductivity, surface photoconductivity, surface photovoltage, internal reflection, electron energy-loss spectroscopy, photoemission, and work function. Recent theoretical studies have also revealed a distinct correlation between geometrical arrangements of the surface atoms and the corresponding band structures of the surface states. However, the atomic positions of the surface atoms used in these calculations are only a model since a detailed analysis of the LEED-intensity-versus-energy curves have not been carried out up to now.     

THz emission from semiconductor surfaces

We provide a review of experimental and theoretical work on electromagnetic terahertz pulse emission from semiconductor surfaces excited by femtosecond laser radiation. The main terahertz emission mechanisms are analysed. The terahertz emission from InAs and Ge is explained by the photo-Dember effect and electric field induced optical rectification. Electronic band structure and carrier scattering mechanisms are investigated by means of terahertz emission and absorption spectroscopy in InAs, InSb and Ge. To cite this article: V.L. Malevich et al., C. R. Physique 9 (2008).     

Analysis of semiconductor surfaces and interfaces

Recent development in the experimental and theoretical analysis of semiconductor surfaces is described. Special attention is given to the Secondary Ion Mass Spectroscopy technique and to its use in the ultrasensitive elemental analysis of semiconductors. Applications to III–V compounds are described.