Heavily-doped Semiconductor Research Articles

Electrical transport properties of SnBi4Te7 and PbBi4Te7with different deviations from stoichiometry

Polycrystalline samples of SnBi4Te7 and PbBi4Te7 withdeviations from stoichiometry in different sublattices were synthesized bymelting and quenching followed by prolonged annealing and hot-pressing. Atroom temperature SnBi4Te7 exhibits both n-type conductivity (Tedeficiency and Sn or Bi excess) and p-type conductivity (Te excess and Sn orBi deficiency) whereas only n-type conductivity samples were obtained forPbBi4Te7 regardless of the type of deviation from stoichiometry. Bothcompounds possess high carrier concentrations in the range4×1019-4×1020 cm-3 and a relatively low carriermobility of 35-70 cm2 V-1 s-1. The electrical resistivity andSeebeck coefficient have been measured over the temperature range 100-800 Kon samples with different deviations from stoichiometry. The temperaturedependence of the electrical transport properties of the compounds is typicalof heavily-doped semiconductors. The potential for thermoelectric applicationsusing these compounds is discussed.

Pressure Dependence of the Barrier Height in Tunnel n-GaAs/Au Junctions

The theory of tunnel current-voltage (I-V ) characteristics of metal-semiconductor junctions based on the self-consistent solution of Poisson equation allows to get the Schottky-barrier height and the charged impurity concentration directly from the tunneling data. This approach was applied to the analysis of the low temperature experiments on tunneling under pressure up to 3GPa in a piston-cylinder gauge. Here we present the barrier height versus pressure for heavily doped n-GaAs(T e)/Au (Ne ∼ 5 −7 � 10 18 cm −3 ) tunnel junctions and compare the obtained pressure dependence of the Schottky barrier with known behavior of the band gap under pressure taking into account the influence of the L- and X-valleys and DX centers. The knowledge of doping level and the potential barrier height at the interface as well as their dependence on pressure is important for studies of the semiconductor structures where the surface band bending region is essential. Our previous works [1, 2] showed that it is possible to carry out qualitative low-temperature tunneling spectroscopy experiments at pressure up to 3 Gpa using stand-alone high-pressure cell. The aim of this work is to extend this technique to quantitative study of band bending region in heavily-doped semiconductors under high pressure. The pinning of the Fermi level that determines the magnitude of Schottky barrier may be attributed to metal-induced gap states [3]. In the particular case of the Au contact to n-GaAs (100) plane the barrier formation was studied by photoemission spectroscopy on Ne = 5 � 10 18

Fermi energy and other related aspects in a parabolic band semiconductor under band tailing

Band tailing refers to the effects of impurity states in and near to the band edge in a heavily-doped semiconductor. In the present study, the Fermi energy, screening length and the impurity screening potential are determined for a heavily-doped parabolic band semiconductor. The effects of unperturbed and perturbed bands are both considered in the evaluation of the entities. In the perturbed band, the density-of-states technique, earlier used by Kane, and the E- dispersion relation technique for band tailing, obtained by us, are applied. Our results on Fermi energy are compared with the results of Kane's model and with those for the unperturbed band for a typical semiconductor of n-type GaAs. We find that our model provides much lower values at a low concentrations of 1017-1018 cm-3, as compared to the other two cases and finally merges with the unperturbed band case at a higher doping conditions. On the other hand, the Kane's model offers much higher values over the doping range studied here.

Aharonov-Bohm Effect at Misfit Dislocations in GaAsSb/GaAs Heterostructures

Here we present the appearance of the quantum Aharonov-Bohm (ΑB) interference [1] in a macroscopic system: semiconductor heterostructure containing an array of misfit dislocations. Let us consider a straight-line dislocation threading a heavily-doped semiconductor crystal. Localized states of the dislocation core (dangling bonds) accept the majority charge carriers from the bulk of material thus making the dislocation to be surrounded by a screening carrier-free cylinder. In GaAs with the carrier concentration of 1017 cm-3 the cylinder diameter is of the order of 100 nm that is presumably smaller than the phase-coherence length of the carrier wave function at liquid-helium temperatures. The charge carrier which meets the dislocation has to pass around the cylinder either clockwise or counter-clockwise. When a magnetic field, B, is applied parallel to the dislocation axis, these two alternative paths are non-equivalent since the vector potential of the magnetic field alters the wave-function phase differently on each path. As a result, the wave function behind the cylinder, which results from the interference of partial waves on these two paths, becomes a periodic function of the magnetic flux enclosed inside the carrier-free cylinder, so that the squared modulus of the wave function will exhibit the period Φ0 = h/e. The

The effects of impurity bands on the electrical characteristics of metal-semiconductor ohmic contacts

The effects of semiconductor heavy doping on the I- V characteristics and the specific contact resistivity ϱ c of semiconductor-metal ohmic contacts have been theoretically studied by incorporating the band-edge-tailing and impurity band effects. The Fermi level and the effective conduction band edge have been recalculated to determine the electron population and the bandgap narrowing. When the available electrons with higher transmission probability, which dominate the tunneling process, have been reduced by the presence of an impurity band, the tunneling current density becomes lower and hence the specific contact resistivity becomes higher for the case with the impurity band than that without the impurity band. Considering the physical properties inherent in a heavily-doped semiconductor, it is possible to explain the deviations of the experimental data from the theoretical results obtained from the conventionally used tunneling theory for the ohmic contacts. Furthermore, by comparing the simulated results and the measured ϱ c data deduced from the Al and Ti contacts on both doping types of the Si-substrate, satisfactory agreements have been obtained.

Photoelectrochemical determination of minority-carrier diffusion length and energy band gap in heavily-doped semiconductors—I. Hole diffusion transport in degenerate n-CdO

A new approach is suggested for determining parameters of heavily-doped semiconductors from photoelectrochemical (PEC) data. Unlike conventional PEC methods, it allows the evaluation of minority-carrier diffusion length ( L) and the energy band gap ( E g) when the photocurrent across the semiconductor-electrolyte junction is affected by interfacial kinetics. The applicability of this approach is demonstrated for polycrystalline degenerate n-CdO. It has been found that there are three valence-band valleys differing in physical and electrochemical parameters for n-CdO minority carriers. The percolation mechanism of hole diffusion transport is assumed to explain extremely high L values (10 −4 − 10 −3cm) obtained for semimetallic cadmium oxide.

Optical and infrared absorption study of TMPD-iodine complex

The ultraviolet-visible and infrared absorption spectra of TMPD-iodine (TMPD = N, N, N′, N′-tetramethyl- p-phenylene-diamine) in the form of non-stoichiometric ternary salts (TMPD) 1.5KII 2 and (TMPD) 1.5HII 2 reveal TMPD 0.5 0  TMPD 2+ (KI 3 · 2I 3 −) and (TMPD) 1.5 0H +I 5 − as the ionic structures. The spectra reveal neutral-to-ionic type transition with band splitting and two band transport as the ionization energies are varied. The background and featureless absorption is analyzed to show that the actual large band gaps are smeared out by long Urbach tails and mainly because of an additional shrinkage of the gap due to heavy doping. This is associated with the electron-electron and mainly electron-impurity scattering dominant compared to phonon scattering for the momentum conservation in heavily-doped semiconductors.

Magnetic and electrical properties of sandwich-like lanthanide phthalocyanines

Rare-earth phthalocyanine sandwich compounds and their iodine analogues have been synthesized. Single crystals were obtained by electrochemical means, and magnetic susceptibility measurements on the polycrystalline samples follow the Curie-Weiss law. Room temperature and 77 K EPR spectra at X-band for undoped lutetium phthalocyanine indicate the presence of a free-radical phthalocyanine unit. Doped complexes also show a narrow signal with a g-value of 2.00. D.C. conductivity measurements on pellets in the temperature range 20 to 300 K yielded values on the order of 10 −5 to 10 −7 s cm −1 for the undoped phthalocyanines, and 10 −2 to 10 −4 s cm −1 for the doped ones. The conductivity behavior may be explained in terms of the variable-range hopping mechanism for heavily-doped semiconductors.

MAGNETORESISTANCE OF FeS1.14 SINGLE CRYSTALS FOR B // c

Measurements of the transverse magnetoresistance on natural single crystals of pyrrhotite FeS1.14 revealed a phenomenon of the order The shape of the curves Ap/ p (0) vs. B for different temperatures is explained and the magnitude of the magnetoresistance can be adequately forseen by the s-d model. Theory and material A quantitative theory of magnetoresistance in heavily-doped antiferromagnetic semiconductors has been developed by Nagaev et al. based on the s-d model (I, 21. The basic idea is that indirect exchange via the conduction electrons tends to establish a ferro- magnetic ordering a fact that differenciates the mag- netization of regions of unequal electron concentration due to impurities 131. These spatial fluctuations of magnetization cause a particularly strong scattering of the carriers. This theory predicts that,

Effect of polar vibrations of the crystal lattice on the plasma frequency of heavily-doped semiconductors and correction for calculation of carrier concentration

In heavily-doped polar semiconductors, the polar vibrations of the crystal lattice affect their plasma frequency. Thus, when calculating the carrier concentration from the plasma reflection edge, some correction to the results is necessary.

Temperature dependence of x-ray photoemission spectra: Fermi-sea recoil effects

The effect of temperature on the asymmetry of the X-ray photoemission lineshape of a metal or heavily doped semiconductor is evaluated using a simple one-dimensional model to describe the conduction electrons. Temperature dependent recoil processes are found to be significant for k BT>E F/4, and could be observed in heavily-doped semiconductors, but not in metals at room temperature.

On the Modification of the Einstein Relation for Heavily Doped Semiconductors Having Gaussian Band Tails

physica status solidi (b)Volume 99, Issue 1 p. K55-K60 Short Note On the Modification of the Einstein Relation for Heavily Doped Semiconductors Having Gaussian Band Tails K. P. Ghatak, K. P. Ghatak Institute of Radio Physics and Electronics, University College of Science and Technology, Calcutta Search for more papers by this authorA. K. Chowdhury, A. K. Chowdhury Institute of Radio Physics and Electronics, University College of Science and Technology, Calcutta 2) On leave of absence from the Department of Physics, B.N. College, Patna University, Patna-800004, India.Search for more papers by this authorS. Ghosh, S. Ghosh Institute of Radio Physics and Electronics, University College of Science and Technology, Calcutta Search for more papers by this authorA. N. Chakravarti, A. N. Chakravarti Institute of Radio Physics and Electronics, University College of Science and Technology, Calcutta Search for more papers by this author K. P. Ghatak, K. P. Ghatak Institute of Radio Physics and Electronics, University College of Science and Technology, Calcutta Search for more papers by this authorA. K. Chowdhury, A. K. Chowdhury Institute of Radio Physics and Electronics, University College of Science and Technology, Calcutta 2) On leave of absence from the Department of Physics, B.N. College, Patna University, Patna-800004, India.Search for more papers by this authorS. Ghosh, S. Ghosh Institute of Radio Physics and Electronics, University College of Science and Technology, Calcutta Search for more papers by this authorA. N. Chakravarti, A. N. Chakravarti Institute of Radio Physics and Electronics, University College of Science and Technology, Calcutta Search for more papers by this author First published: 1 May 1980 https://doi.org/10.1002/pssb.2220990158Citations: 9 1) 92 Acharya Prafulla Chandra Road, Calcutta-700009, India. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume99, Issue11 May 1980Pages K55-K60 RelatedInformation

Study of the yellow emission of natural α-HgS

First we present an experimental study of the emission of α-HgS (function of temperature, excitation, lifetime measurements) and give the first conclusions. We show in particular that the emission, which is attibuted to bound—bound transitions at very low temperature and to conduction band-acceptor transitions for T77 K, cannot be described by the recombination models generally used. Secondly, we interpret the yellow luminescence in terms of heavily-doped semiconductors, in which the discrete impurity levels are replaced by bands of states. We present a conduction band-to-acceptor band of states transition model in which the impurity density of states is described by the expression p ∞ exp − ( E−Eλ) 2 2γ 2 We show that the application of this model to the yellow emission reveals an acceptor band of states with the characteristics: E A ≅ 85 meV and γ ≅ 25 meV, and two “discrete” donor levels with ∽5 and ∽40 meV binding energy.

On the electronic structure of an impurity band: a cumulant approach

The electronic structure of an impurity band in a heavily-doped semiconductor, in the metallic regime just above the Mott transition, is studied in a tight-binding scheme using a cumulant expansion. The density of states shows no erosion in its centre near the impurity level; a result confirmed by a detailed comparison between results obtained either by a numerical simulation technique or by other analytical approaches. This comparison also shows that within a single-site framework, very different results can be obtained at the extremities of the spectrum whereas converging results are obtained at its centre. Possible extensions to cases where short-range order effects are important, such as in liquid-metal systems, are also discussed.

Ordinary Magnetoresistance of Heavily Doped Semiconductors at Low Temperatures in a Weak Magnetic Field

AbstractThe ordinary longitudinal and transverse magnetoresistance of electrons at low temperatures in a weak magnetic field is calculated from a simplified model of heavily doped semiconductors. The treatment which is based on the Green's function methods using Feynman‐path integral formulation, is applied to disordered systems and developed already in five previous papers. Two important cases are discussed within the present model. In the first one, an ordinary n‐type semiconductor is considered, assuming that the carrier concentration is equal to the donor concentration; in the second case, the carrier concentration rises as the third root of the total concentration of impurities.

Theory of the Donor-Dependence of Electron Mobility in Degenerate Germanium

A new theory of screening of donor ions in heavily-doped semiconductors is proposed which takes into account the specific nature of the impurity ions. The salient features of the resulting donor ion potentials are the following. The screening of the ions arising from the conduction electrons extends over a spherical shell whose inner radius is the Slater radius of a donor ion and whose outer radius is half of the distance between two donor ions. At the inner radius the donor ion potential assumes the potential of the free donor ion while at the outer radius the potential vanishes. Mobility considerations using the proposed potentials account for the experimental finding that at the same electron concentration and temperature the electron mobility in Sb-doped Ge is larger than that in As-doped Ge. Further considerations are compatible with the additional experimental finding that at the same electron concentration and temperature the electron mobility in P-doped Ge is smaller than that in Sb-doped Ge but l...