The electrical properties of doped silicon,grown by Molecular-Beam-Epitaxy (MBE)

Measurements of the Hall coefficients and of the resistivity of MBE-grown Si, doped with P, As, Sb, B, and Ga in the concentration range 10¹⁴ to 10²⁰ cm^–3, were carried out at 77 K and at 300 K. With the exception of Ga-doped Si, the measured mobilities were close to or higher than those of bulk materials at both temperatures. The Mott metal/non-metal transition has been observed in the present epitaxial materials and the measured values for the critical impurity concentration at which the transition occurs, agree with values reported by other workers for bulk silicon.     

Effect of in addition on some physical properties of the As2Se3 amorphous system

The effect of In content on do electrical conductivity and DTA of the system (As₂Se₃)_1-x. In_x, x=0, 0.01, 0.05, has been studied. The electrical energy gap was found to increase for an In content 0.01% and decrease for an In content 0.05%. The samples exhibit the three conduction mechanisms proposed by Mott and Davis. The activation energy was calculated for each mechanism. The effect of heating rate on the transition temperatures (T _g,T _c,T _m) was studied and the variation of the crystallization-peak position was used to calculate the activation energy and the order of the crystallization process.     

General electrical transport properties of polycrystalline multi-layered metallic thin films

We have derived, following the recent theoretical calculation of the electrical conductivity of multi-layered metallic thin films, a general solution of the electrical conductivity for those films with grain structures, since those structures give important contributions to the electrical transport properties of polycrystalline thin film. The temperature coefficients of resistivity have also been obtained.     

Semiconductor interface studies using core and valence level photoemission

The application of core and valence level photoelectron spectroscopy to the study of semiconductor heterojunctions and metal-semiconductor interfaces (Schottky barriers) is outlined, with an emphasis on recent results and their explanation in terms of current theories. While the determination of transport barriers (valence band offsets and Schottky barriers) is stressed, the identification of chemical reactions at the interface is also discussed using several examples. Photoemission can precisely determine many important quantities in these junctions; also demonstrated, however, is the disturbing influence of the photoemission process itself through the creation of a surface photovoltage in metal-semiconductor interfaces, and its possible consequences for recent investigations of Schottky barrier heights in metal overlayers on low temperature substrates.     

The role of the interfacial SiOx layer in SnO2/n-Si photocells

It is proposed that the charge transport across the SiO _x layer at the interface SnO₂/Si proceeds by a hopping mechanism. During heat treatment of the photovoltaic cells, in air, chemical reactions occur with O₂/H₂O, which lead to a drastic reduction of the density of hopping sites near the Si conduction band edge. The SiO _x hopping sites of energy near the valence band edge are less affected by these chemical reactions. Thus, photogenerated holes can still pass the barrier while the dark current flow is strongly inhibited.     

Structural, optical and electrical properties of ZnO and ZnO-Al2O3 films prepared by dc magnetron sputtering

ZnO and ZnO-Al₂O₃ thin films were prepared by dc magnetron sputtering and their structural, optical and electrical properties were studied comparatively. It is discovered that the ZnO-Al₂O₃ thin films remain transparent in a shorter wavelength range than the ZnO films, resulting from the increase of their band gap. Their resistivity decreases by seven orders of magnitude, which is caused by doping of Al to ZnO grains in the film. Preferential orientation of ZnO grains in the ZnO-Al₂O₃ thin films deteriorates because of the existence of Al₂O₃ impurity phase in the film. Received: 5 January 1999 / Accepted: 11 October 1999 / Published online: 8 March 2000     

The effect of H-dilution on the transport properties of doped a-Si1−x Ge x : H alloys

This paper is concerned with the optimization of growth conditions for a-Si_1-x Ge _x :H alloys. It is shown that H-dilution of source gases selectively improves the band transport of electrons without significantly affecting the recombination center density or the band transport of holes. It is further shown that the beneficial effects of H-dilution are most pronounced in alloys with comparable densities of Si and Ge.     

On the annealing behaviour of the Staebler-Wronski effect ina-Si:H

The kinetics of the Staebler-Wronski effect ina-Si:H were investigated experimentally. The rate of recovery from the illuminated state B to the annealed state A was observed at various temperatures in undoped,n- andp-dopeda-Si:H. The data can be characterized by a thermally activated relaxation time with an activation energy decreasing with increasing doping concentration. The results are compared with previous data and existing models.     

Dielectric and interfacial properties of InP plasma-grown oxides

Methods of dielectric analysis have been employed to investigate the frequency dispersion of InP-oxide dielectric in MOS and MOM devices. The Cole-Cole empirical method has indicated a wide range of relaxation time for the interfacial polarization. This has been interpreted in terms of a model of carrier injection from the gate metal into the oxide gap states. The model is proposed in conjunction with the anomalous hysteresis in the MOM C-V characteristics and could be applied to other MIS systems.Formerly with the department of Engineering, Cambridge University, U.K.     

Structural and electrical properties of Au/Pt/Ti ohmic contacts to degenerated doped n-GaAs

The ohmic contact characteristics of Au/Pt/Ti on degenerated doped n-GaAs were evaluated. Structural and electrical properties were studied by means of X-ray diffraction (XRD), Auger Energy Spectrum (AES) and a HP4145B parameter analyzer. The structural analysis revealed a TiAs phase in the interface between metal multilayer and GaAs at higher annealing temperatures. Electrical measurement showed a minimum ohmic contact resistance of 3×10^-4 Ω cm². The dominant current mechanism was found to be thermionic emission with a barrier height of Φ_b, of 0.09 V by comparing the experimental data with different theoretical models. Received: 14 December 2001 / Accepted: 4 April 2002 / Published online: 22 November 2002 RID="*" ID="*"Corresponding author. Fax: +86-21/6226-4397, E-mail: zhoujian999@163.net     

Nature of the high-pressure transition in Fe2O3 hematite

We present a new method to separate the crystallographic and electronic phase transitions in hematite using x-ray emission spectroscopy and x-ray diffraction. Our observations, based on the behavior of a metastable high-pressure phase in the stability domain of the low-pressure phase, show that the electronic transition is preempted by the crystallographic transition. The former occurs only afterwards in the high-pressure phase, possibly as a result of a Mott transition. The idea that the electronic transition drives the transition in hematite is therefore invalidated. Such methods should help elucidate the mechanics and the driving forces behind a number of first-order high-pressure phase transitions.     

Mechanism of conductivity in metal-polymer-metal structures

Received: 25 September 1998 / Accepted: 25 November 1998 / Published online: 24 February 1999     

The influence of a HF and an annealing treatment on the barrier height of p- and n-type Si MIS structures

In this paper, the influence of two pre-evaporation surface treatments on the electrical characteristics of n- and p-Si/Au, Cr and Ti MIS diodes are studied. A strong dependence of the barrier height on the pre-evaporation treatment is observed and is found to be independent of the metal work function. In order to explain this, it is suggested that the interfacial charges are strongly affected by the pre-evaporation treatment used.     

Transport and optical properties of amorphous carbon and hydrogenated amorphous carbon films

In this paper we report on the electrical and optical properties of amorphous carbon (a-C) and hydrogenated amorphous carbon (a-C:H) films. Resistivity of both types of films decreases with increase in temperature. At lower temperatures (60-250 K) the electron transport is due to variable range hopping for the a-C films. At higher temperatures (300-430 K) it is thermally activated for both types of films. Analysis of the heterojunction between diamond-like carbon (DLC) and bulk silicon (Si) leads to the conclusion that our a-C films are of n-type and our a-C:H films are of p-type. The optical measurements with DLC revealed a Tauc bandgap of 0.6 eV for the a-C films and 1-1.2 eV for the a-C:H films. An Urbach energy around 170 meV could be determined for the a-C:H films. Strain versus resistance plots were measured resulting in piezoresistive gauge factors around 50 for the a-C films and in between 100 and 1200 for the a-C:H films.     

Effect of annealing on the electrical properties and refractive index of HgI2 single crystals

The effect of annealing on the electrical properties and the refractive index of red mercuric iodide (HgI₂) single crystals is investigated. The ac-impedance and phase angle were measured in the frequency range from 100 Hz to 10 kHz at different annealing temperatures. The ac-conductivity, dielectric constants, loss tangent and the refractive index as a function of frequency are determined. The results are discussed in terms of structural changes taking place as a result of the heat treatment of the HgI₂ single crystals.     

The effect of interface states, excess capacitance and series resistance in the Al/SiO2/p-Si Schottky diodes

The current-voltage (I-V) characteristics of Al/SiO₂/p-Si metal-insulator-semiconductor (MIS) Schottky diodes were measured at room temperature. In addition the capacitance-voltage (C-V) and conductance-voltage (G-V) measurements are studied at frequency range of 10 kHz-1 MHz. The higher value of ideality factor of 3.25 was attributed to the presence of an interfacial insulator layer between metal and semiconductor and the high density of interface states localized at Si/SiO₂ interface. The density of interface states (N_ss) distribution profile as a function of (E_ss − E_v) was extracted from the forward bias I-V measurements by taking into account the bias dependence of the effective barrier height (Φ_e) at room temperature for the Schottky diode on the order of ≅4 × 10¹³ eV⁻¹ cm⁻²_. These high values of N_ss were responsible for the non-ideal behaviour of I-V and C-V characteristics. Frequency dispersion in C-V and G-V can be interpreted only in terms of interface states. The N_ss can follow the ac signal especially at low frequencies and yield an excess capacitance. Experimental results show that the I-V, C-V and G-V characteristics of SD are affected not only in N_ss but also in series resistance (R_s), and the location of N_ss and R_s has a significant on electrical characteristics of Schottky diodes.     

Surface conduction mechanisms and the electrical properties of Al2O3 humidity sensor

The electrical properties of Al₂O₃ humidity sensor are governed by the variations in the surface conductivity of a porous anodic Al₂O₃ film with humidity. We propose a two-carrier mechanism to describe charge transport on porous alumina. At low humidities, a phonon-induced electron tunneling is postulated between donor water sites; at high humidities protonic conduction dominates. A physical model of surface conduction is developed using energy-band concepts. Based on this model, theoretical expressions are presented for the surface conductivity. The model predicts a log-normal distribution of surface conductivity amongst the pores which conforms to the observed electrical properties of the sensor. The experimental plot of log σ versus T^-1 shows that the activation energy varies on transition from the liquid-water state to electron tunneling on the hydroxylated surface. The model also prescribes the Al₂O₃ film-growth parameters for low-and high-humidity sensors which will be useful for fabricating devices of desired response characteristics.     

Local states of iron in iron implanted hematite Fe2O3

Powder samples of⁵⁷Fe₂O₃ and⁵⁶Fe₂O₃ were implanted with⁵⁶Fe and⁵⁷Fe ions, respectively. By the use of Conversion Electron Mössbauer Spectroscopy it was possible to observe the local states of implanted ions (⁵⁷Fe in⁵⁶Fe₂O₃) or the states of iron atoms from the target which were displaced during implantation due to the ballistic processes (⁵⁶Fe in⁵⁷Fe₂O₃). The implanted and displaced iron atoms appear in three different states: (i) in regular substitutional positions of Fe₂O₃, (ii) as magnetite Fe₃O₄-type structures and (iii) paramagnetic FeO_1?x state. The observed fractions of each state agree rather well with the calculated values obtained from the local iron atom enrichment at the surface as well as from the analysis of the equilibrium phase diagram for the binary Fe?O system. However, in⁵⁷Fe implanted samples some enhancement of the FeO_1?x fraction was found in comparison with the⁵⁶Fe implanted hematite.     

Current instabilities in dynamic random access memory storage capacitor formed with electron beam deposited Y2O3 dielectric

Metal-oxide-semiconductor (MOS) storage capacitors based on electron beam deposited Y₂O₃ extrinsic dielectric on Si show changes in capacitance density depending on the amorphous and crystalline phases. Bias stress cycle-dependent changes in capacitance density occur due to the non-equilibrium nature of defect states at the Y₂O₃/Si interface after O₂ annealing as a result of the emergence of a 4–8 nm thick SiO₂ film at the interface. Leakage currents show instability under repeated dc bias stress, the nature and extent of which depend upon the structure of the Y₂O₃ gate dielectric and the polarity of dc bias. With amorphous Y₂O₃, leakage currents drift to lower values under gate injection due to electron trapping, and to higher values under Si-injection due to the generation of holes. Though leakage current drift is minimal for crystalline Y₂O₃, its magnitude increases as the energy of injected electrons from mid-gap states is low and the local field due to asperity is high. The emergence of interfacial SiO₂ reduces the magnitude of Si-injection leakage current substantially, but causes transient changes resulting in switching to higher values at a threshold dc bias. Thermal detrapping of holes and reverse bias stress studies confirm that the instability of current is caused by an increase in the cathodic field from hole trapping at interface states. Leakage current instability limits the application of extrinsic high dielectric constant dielectrics in a high density DRAM storage capacitor, unless a new interface layer scheme other than SiO₂ and a method to form a defect-free dielectric layer can be implemented. Received: 29 October 2001 / Accepted: 22 April 2002 / Published online: 4 December 2002 RID="*" ID="*"Corresponding author. Fax: +1-413/545-4611, E-mail: rastogi@ecs.umass.edu     

Ferryl (Fe=O) termination of the hematite alpha-Fe2O3(0001) surface

Using scanning tunneling microscopy and infrared reflection absorption spectroscopy we have observed that the alpha-Fe2O3(0001) surface exhibits ferryl (Fe=O) groups, which may coexist with domains of the Fe-terminated surface. We therefore fully support ab initio calculations recently reported in the literature [W. Bergmeyer, H. Schweiger, and E. Wimmer, Phys. Rev. B 69, 195409 (2004)]. The close similarity to the results on the (0001) surfaces of Cr2O3 and V2O3 strongly suggests that the M=O termination under certain oxygen pressure conditions is the most stable for the close-packed surfaces of transition metal oxides with the corundum structure.