Concentration Of Impurity Ions Research Articles

Electric field broadening of arsenic donor states in strongly compensated n-type Ge:(As, Ga)

We discuss on the broadening of ground-state to bound excited-state transitions of shallow donors in strongly compensated n-type Ge in the presence of electric fields and their gradients arising from randomly distributed ionized impurities. Low-temperature ( T=3.2 K ) far-infrared absorption spectra of strongly compensated n-type Ge:(As,Ga) have been obtained for samples having ionized impurity concentration N I =2.2×10 13–2.6×10 14 cm −3 . Absorption peaks corresponding to 1s–2p ± transition of arsenic impurities are observed, and broadened linearly with the ionized impurity concentration due to interactions between electrons and the quadrupole moments of ionized donors. The slope of the peak line width plotted against N I changes at N I ≈8×10 13 cm −3 due to the transition of ionized impurity distribution from random ( N I <8×10 13 cm −3 ) to correlated ( N I >8×10 13 cm −3 ).

Radially and axially resolved Thomson scattering in a gas-linerpinch

We performed spatially and temporally resolved Thomson scatteringin a plasma generated in a gas-liner z-pinch, where the amount ofaxially distributed impurity ions seeded in a hydrogen plasma canbe controlled. The parameters of the plasma electron density,temperature, concentration of impurity ions as well as the bulkvelocity of the plasma are measured along both the radius and thez-axis. The temporal behaviour is studied from shot to shot.Depending on the impurity concentration on the axis and the kindof impurities, the homogeneity and stability of the plasmacolumn along the z-axis are investigated. For small impurityconcentrations the impurity ions are located in the homogeneouscentral part of the plasma offering excellent conditions to testtheories on Stark broadening of spectral lines. Modulations of thedensity and temperature along the axis start to rise when theconcentration of the impurity ions exceed a certain limitdepending on their charge number. The modulations are related toRayleigh-Taylor instabilities growing during the late phase of thecompression.

Fast Lithium Beam Edge Plasma Spectroscopy at IPP Garching—Status and Recent Developments

Impurity ion concentration and impurity ion temperature in the plasma gradient region as well as the scrape-off layer are essential parameters for understanding the physics of L- and H-mode transport and the transport barrier itself. To gain access to these properties, the well-established Li-beam diagnostic capabilities on both fusion devices at the Max-Planck-Institut für Plasmaphysik (IPP) Garching [WENDELSTEIN 7-AS stellarator and the Axially Symmetric Divertor Experiment (ASDEX) Upgrade tokamak] have been extended to include the measurement of radial profiles of impurity ion densities and temperatures by means of charge-exchange spectroscopy. This paper describes the experimental setups on both devices and presents typical results of impurity ion investigations. Electron density measurements show excellent agreement with other diagnostics. In addition, several LiI spectral lines (2p to 2s, 3d to 2p, 4s to 2p, and 4d to 2p) have been measured to check the collisional-excitation Li-beam modeling, especially for collision processes involving higher Li(nl) states (n ≥ 3). The underlying database has been augmented by extensive investigations of lithium excitation processes. Cross sections for Li(2s to 2p) excitation by various impurity ions as well as proton impact Li(2l to nl) excitation have been calculated and measured in detail.

Band gap narrowing in n-type and p-type 3C-, 2H-, 4H-, 6H-SiC, and Si

Doping-induced energy shifts of the conduction band minimum and the valence band maximum have been calculated for n-type and p-type 3C-, 2H-, 4H-, 6H-SiC, and Si. The narrowing of the fundamental band gap and of the optical band gap are presented as functions of ionized impurity concentration. The calculations go beyond the common parabolic treatments of the ground state energy dispersion by using energy dispersion and overlap integrals from band structure calculations. The nonparabolic valence band curvatures influence strongly the energy shifts especially in p-type materials. The utilized method is based on a zero-temperature Green’s function formalism within the random phase approximation with local field correction according to Hubbard. We have parametrized the shifts of the conduction and the valence bands and made comparisons with recently published results from a semi-empirical model.

Growth, doping and characterization of epitaxial thin films and patterned structures of AlN, GaN, and AlxGa1−xN

Abstract Advancements in the doping of GaN and AlxGa1−xN thin films, and the growth of GaN and AlxGa1−xN structures on patterned heterostructure substrates via metalorganic vapor phase epitaxy are reported. The acceptor-type behavior of Mg-doped GaN films grown in N2 diluents is presented. Net ionized impurity concentrations up to 8×1018 cm−3 and Hall mobilities up to ≈14 cm2 V−1 s−1 were measured for Mg-doped films grown in N2 in the as-grown condition. Donor and acceptor doping of AlxGa1−xN alloys was performed. Acceptor doping of AlxGa1−xN for x≤0.13 and donor doping for x≤0.58 were achieved for films deposited at 1100 °C. Lateral epitaxial overgrowth of GaN and AlxGa1−xN layers was investigated. The growth and coalescence of GaN and AlxGa1−xN stripes patterned in SiO2 and/or SiNx masks deposited on GaN, including aligned second lateral epitaxial overgrowth on initial laterally overgrown GaN layers, are discussed.

Effect of Growth Conditions on Electrical Properties of Si-Doped In0.52Al0.48As Grown by Metalorganic Vapor Phase Epitaxy

A systematic study of the electrical properties of Si-doped In0.52Al0.48As grown under various metalorganic vapor phase epitaxy (MOVPE) conditions such as V/III ratio and growth temperature is carried out. It is demonstrated that either high V/III ratios (≥64) or high growth temperatures (≥720°C) are necessary for obtaining good InAlAs electrical properties. For a small V/III ratio (=32) and low growth temperatures (≤700°C), a large discrepancy is found in Hall carrier concentration (nHall), ionized impurity concentration (NC – V), and Si concentration (NSi); NC – V>NSi>nHall; which can be explained by the dual formation of donor and acceptor deep levels. SIMS results suggest that carbon and oxygen impurities are not candidates for these deep levels, and other origins such as intrinsic defects, which are closely related to growth conditions, are applicable.

Study of Transport Properties in (CrO4)2— Doped KI Crystals

The ionic conductivity of pure and chromate anion doped KI crystals was measured in the temperature range 200 to 600 °C. A large contribution of conductivity in pure KI crystals due to cation as well as anion vacancies was observed at high temperature. The solubility of (CrO 4 ) 2- in KI crystals was also examined and it is shown that the solubility is good compared to other alkali halide systems like KCI, KBr, NaCI, NaBr, etc. The ionic conductivity measurements were made on pure KI crystals and KI crystals doped with 0.1, 0.3 and 0.5 mol% of chromate ion in the asgrown state. Further the conductivity is measured on KI crystals doped with 0.5 mol% of chromate ion and also on samples quenched from higher temperature and on annealed ones. From the conductivity (log σT) versus temperature (10 3 /T) plots, it is observed that the conductivity decreases in low and high temperature regions with increasing concentration of impurity ions. The decrease in conductivity in the low temperature region is explained on the basis of the formation of complexes with background impurities, formation of neutral pairs, etc. The increase and decrease in conductivity due to quenching and annealing is explained on the basis of dissociation and aggregation of complexes etc. The corresponding activation energies are evaluated and compared with previously reported values on various alkali halides.

Study of Transport Properties in (CrO4)2 Doped KI Crystals

The ionic conductivity of pure and chromate anion doped KI crystals was measured in the temperature range 200 to 600 °C. A large contribution of conductivity in pure KI crystals due to cation as well as anion vacancies was observed at high temperature. The solubility of (CrO(CrO4)2— in KI crystals was also examined and it is shown that the solubility is good compared to other alkali halide systems like KCl, KBr, NaCl, NaBr, etc. The ionic conductivity measurements were made on pure KI crystals and KI crystals doped with 0.1, 0.3 and 0.5 mol% of chromate ion in the as-grown state. Further the conductivity is measured on KI crystals doped with 0.5 mol% of chromate ion and also on samples quenched from higher temperature and on annealed ones. From the conductivity (log σ T versus temperature (103/T plots, it is observed that the conductivity decreases in low and high temperature regions with increasing concentration of impurity ions. The decrease in conductivity in the low temperature region is explained on the basis of the formation of complexes with background impurities, formation of neutral pairs, etc. The increase and decrease in conductivity due to quenching and annealing is explained on the basis of dissociation and aggregation of complexes etc. The corresponding activation energies are evaluated and compared with previously reported values on various alkali halides.

Electron transport characteristics of GaN for high temperature device modeling

Monte Carlo simulations of electron transport based upon an analytical representation of the lowest conduction bands of bulk, wurtzite phase GaN are used to develop a set of transport parameters for devices with electron conduction in GaN. Analytic expressions for spherical, nonparabolic conduction band valleys at the Γ, U, M, and K symmetry points of the Brillouin zone are matched to experimental effective mass data and to a pseudopotential band structure. The low-field electron drift mobility is calculated for temperatures in the range of 300–600 K and for ionized impurity concentrations between 1016 and 1018 cm−3. Compensation effects on the mobility are also examined. Electron drift velocities for fields up to 500 kV/cm are calculated for the above temperature range. To aid GaN device modeling, the drift mobility dependences on ambient temperature, donor concentration, and compensation ratio are expressed in analytic form with parameters determined from the Monte Carlo results. Analytic forms are also given for the peak drift velocity and for the field at which the velocity peak is reached as functions of temperature.

Monte Carlo calculation of velocity-field characteristics in II-VI compound semiconductors

The velocity field characteristics of II–VI compound semiconductors at 77K have been obtained by the Monte Carlo simulation technique. The results agree with the available experimental data and with those obtained by solving the Boltzmann Transport Equation analytically. The simulation technique is described in detail and various aspects regarding the convergence of the simulation are discussed. The carrier distribution function has also been obtained from the simulation. The effects of the various simulation parameters, as well as those of the ionized impurity concentration, on the mobility values for the different semiconductors are discussed and results are presented.

EPR studies of phase transitions in cadmium calcium acetate hexahydrate as a function of different paramagnetic impurity-ion concentrations

The phase transition in cadmium calcium acetate hexahydrate (CCDAH) has been studied in detail with electron paramagnetic resonance (EPR) as a function of two different paramagnetic ion concentrations, namely, ${\mathrm{Cu}}^{2+}$ and ${\mathrm{Mn}}^{2+}$ ions. The change in transition temperature (122--143 K) with ${\mathrm{Cu}}^{2+}$ ion concentrations is explained in terms of mean-field theory and a soft vibrational mode of the -${\mathrm{C}\mathrm{a}\ensuremath{-}\mathrm{C}\mathrm{d}}_{1\ensuremath{-}x}{\mathrm{Cu}}_{x}\ensuremath{-}\mathrm{Ca}$- chain along the $c$ axis of the crystal. While the same theory can also explain our observed transition temperature (118--128 K) as a function of the ${\mathrm{Mn}}^{2+}$ ion concentration in this crystal, it does not explain why the limiting value of the transition temperature (i.e., 145 K) of ${\mathrm{CaCd}}_{1\ensuremath{-}x}{\mathrm{Cu}}_{x}{(\mathrm{C}\mathrm{H}}_{3}{\mathrm{C}\mathrm{O}\mathrm{O})}_{4}{\mathrm{\ensuremath{\cdot}}6\mathrm{H}}_{2}\mathrm{O}$ as $x$ tends to zero, is strikingly different from the limiting value of $(\ensuremath{\sim}128.4\mathrm{K})$ of ${\mathrm{CaCd}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}{(\mathrm{C}\mathrm{H}}_{3}{\mathrm{C}\mathrm{O}\mathrm{O})}_{4}{\mathrm{\ensuremath{\cdot}}6\mathrm{H}}_{2}\mathrm{O}$ as $x$ tends to zero. The same theory also successfully explains the absence of any phase transition in isomorphous ${\mathrm{C}\mathrm{a}\mathrm{C}\mathrm{u}(\mathrm{C}\mathrm{H}}_{3}{\mathrm{C}\mathrm{O}\mathrm{O})}_{4}{\mathrm{\ensuremath{\cdot}}6\mathrm{H}}_{2}\mathrm{O}.$ The value of $\ensuremath{-}{\mathrm{dT}}_{c}/dx$ is significantly higher with ${\mathrm{Mn}}^{2+}$ than with ${\mathrm{Cu}}^{2+}$ in CCDAH.

Ultra-pure water for ion chromatography

Water with ionic concentrations substantially below 1 μg/l is an increasing requirement for high sensitivity ion chromatographic analysis. The resistivity of the water is not an adequate guide to impurity levels at less than 1 μg/1 due to the practical limitations in resistivity measurement and to the non-linear variation of resistivity with impurity ion concentration. A water purification system is described using inter-stage monitoring to overcome these limitations and to ensure ultra-trace ionic levels. Some examples of cation analyses are included.

Thermoluminescence dosimetric properties of beryllium oxide

Beryllium oxide (BeO) displays strong thermoluminescence (TL) together with tissue - equivalent properties which underline its application as a TL dosimeter. In the dosimetry of X- and γ-rays some of the advantages of BeO over other TL materials are its commercial availability, low cost, chemical inertness, non-toxicity (as a ceramic), high sensitivity to ionizing radiations, good reproducibility of response, low fading, absence of low-temperature peaks and moderate energy dependence. Various authors have reported glow curves of BeO TL phosphor, whose dominant dosimetric peak lies between about 160 and 200 °C. The position of this peak, however, depends upon the type of the radiation used for exciting the phosphor. Although fading of TL is nominal when kept in the dark, the γ-exposed BeO phosphors fade faster when exposed to ambient light. When exposed to γ-radiation, these phosphors exhibit linearity from a minimum of about 1 mrad (1 rad =10-2 gray) up to approximately 10 rad, above which there is supralinear behaviour, and the concentration of impurity ions in BeO is reported to expand the linearity region. Ceramic samples have been reported to exhibit a roughly flat response when exposed to X-rays of 30–115 keV and γ-rays of 60Co. Because their response to thermal neutrons is negligible compared to the γ-response, the use of BeO has been suggested to measure the γ-component in the (n, γ) mixed fields.

Deep levels, electrical and optical characteristics in SnTe-Doped GaSb Schottky Diodes

The GaSb layers investigated were grown directly on GaAs substrates by molecular beam epitaxy (MBE) using SnTe source as the n-type dopant. By using admittance spectroscopy, a dominant deep level with the activation energy of 0.23-0.26 eV was observed and its concentration was affected by the Sb4/Ga flux ratio in the MBE growth. A lowest deep-level concentration together with a highest mobility was obtained for GaSb grown at 550°C under a Sb4/Ga beam equivalent pressure (BEP) ratio around 7, which should correspond to the lowest ratio to maintain a Sb-stabilized surface reconstruction. In the Hall measurement, an analysis of the temperature-dependent mobility shows that the ionized impurity concentration increases proportionally with the sample’s donor concentration, suggesting that the ionized impurity was introduced by an SnTe source. In addition, optical properties of an undoped p-, a lightly and heavily SnTe-doped GaSb layers were studied by comparing their photoluminescence spectra at 4.5K.

Time-resolved luminescence studies of heavily nitrogen doped ZnSe

Time-resolved luminescence data from heavily nitrogen doped ZnSe (total N concentration exceeding mid-1018/cm3) is presented. The luminescence exhibited a decay time and a rise time which increased with decreasing energy of observation. Furthermore, both the decay times and rise times decreased with increasing temperature. These observations are consistent with the following model: (i) a band of states is created due to fluctuations in the ionized impurity concentrations; (ii) a portion of the carriers captured by the shallower impurity states are transferred to deeper states prior to recombination.

Scattering reduction due to electron wave interference by periodic doping of impurity ions in semiconductors

The scattering probability of a Fermi energy electron was analyzed for a semiconductor crystal where a finite number of doped impurity ions are placed periodically. Due to electron wave interference scattering for periodic placement is reduced in comparison with that for random placement. The scattering reduction depends on the boundary shape of the Brillouin zone of the superlattice of impurity ions, the number and the concentration of impurity ions and the propagation direction. When 2331 impurity ions are placed in 250 × 250 × 250 nm 3 (body-centered-cubic), the scattering probability for [111] propagation is 1 5 of that for random placement.

Theoretical Study of Resonant Tunneling Diodes with Impurity Ions Located in Wells

Transmission characteristics of resonant tunneling diodes (RTDs) with impurity ions in wells are analyzed using a two-dimensional model. The impurity ions are found to result in the transmission energy spectrum having a double-peak shape with intrinsic and impurity-assisted peaks. The appearance of the impurity-assisted peak explains previously reported experimental observations. The height of the impurity-assisted peak depends on the concentration of impurity ions in the well. Impurity ions in the well may broaden the intrinsic peak width, which should be taken into consideration in the estimation of the electron coherence using the resonance energy width of RTDs.

Evaluation of GaAs Wafer Using Noncontact Capacitance/Voltage Measurement

A new noncontact capacitance/voltage ( C–V ) measurement technique which enables the application of semiconductor materials without insulator film on the surface is introduced. The applicability of this technique has been verified by measuring oxidized silicon wafers whose characteristics were well investigated. Based on the general theory of metal-oxide-silicon (MOS) system, the derivation of ideal C–V curves under various conditions was discussed for the analysis of the measured C–V curves. Then, GaAs wafers subjected to various processing steps were evaluated. The behaviors of the measured C–V curves not only agreed with the results reported earlier but led to detection of the thermal annealing effect of the interface traps at low temperature. Furthermore, the ionized impurity concentration was determined from the (1/C)2 plots and the inversion capacitance, and it was found that the difference between their determined values was related to the density of the bulk traps.

Evidence for correlated hole distribution in neutron-transmutation-doped isotopically controlled germanium.

We report on low-temperature infrared-absorption spectroscopy studies of compensated p-type Ge(Ga,As) samples with varying doping compensation ratios. Previous difficulties in preparing appropriate samples are overcome by neutron-transmutation doping of high-purity, isotopically controlled germanium composed exclusively of $^{70}\mathrm{Ge}$ and $^{74}\mathrm{Ge}$, viz. $^{70}\mathrm{Ge}_{\mathit{x}}$ $^{74}\mathrm{Ge}_{1\mathrm{\ensuremath{-}}\mathit{x}}$. With this technique, we have produced a series of crystals with compensation ratios between 0.082 and 0.87, while maintaining the net-acceptor concentration [Ga]-[As] constant at 5\ifmmode\times\else\texttimes\fi{}${10}^{14}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$. The observed excitation lines of Ga acceptors broaden linearly with the ionized impurity concentration due to the quadrupole interactions between Ga bound holes and the electric-field gradient. Experimental linewidths are quantitatively compared with existing theories of electric-field broadening developed in the context of donor transitions. We find excellent agreement with the theory based on the correlated distribution of ionized impurity centers. \textcopyright{} 1996 The American Physical Society.

Collisional-radiative modeling of the L-shell emission of Mo30+ to Mo33+ emitted from a high-temperature-low-density tokamak plasma.

The x-ray spectra of several highly stripped molybdenum ions have been recorded between 0.6 and 5.5 A in the Frascati tokamak upgrade with a rotating crystal spectrometer. Detailed, quasi-steady-state collisional-radiative models have been used to interpret emission features from inner shell, electron impact excitations in molybdenum ions near the neonlike charge state and to characterize the charge state distribution in the plasma. Processes such as resonant excitation, excitation autoionization, and dielectronic recombination have been included in the models of the molybdenum ions{close_quote} emission features. Introducing the excitation-autoionization process into ionization equilibrium calculations brings agreement between observations and calculations of the relative ionization equilibrium fractions of highly stripped molybdenum ions. Absolutely calibrated spectra and detailed models for the excitation processes in these molybdenum ions allow us to calculate crucial plasma parameters, such as the concentration of impurity ions in the plasma and the amount of power lost from the plasma through impurity line radiation. {copyright} {ital 1996 The American Physical Society.}