Impurity Ionization Energy Research Articles

Insight into Carrier and Phonon Transports of PbSnS2 Crystals.

The simultaneous optimization of n-type and p-type thermoelectric materials is advantageous to the practical application of the device. As an emerging thermoelectric material, PbSnS2 exhibits highly competitive thermoelectric properties due to its unique carrier and phonon transport characteristics. To promote the utilization of this low-cost thermoelectric material, p-type PbSnS2 crystals are synthesized and optimized through Na doping and Se alloying. The resulting thermoelectric transport properties differ significantly from those reported for n-type crystals, prompting us to compare and analyze both n-type (Cl-doped) and p-type (Na-doped) PbSnS2 crystals from various perspectives. Cl doping is subject to weaker "Fermi pinning" and lower impurity ionization energy compared with Na doping, leading to higher doping efficiency. The different optimal performance directions in n-type and p-type crystals can be attributed to the distinct charge density distributions near the conduction band minimum (CBM) and the valence band maximum (VBM). Additionally, both n-type and p-type crystals exhibit ultralow lattice thermal conductivity due to the low symmetry of their twisted NaCl structure combined with the strong anharmonicity. This comprehensive analysis of PbSnS2 crystals provides a solid foundation for further performance optimization and device assembly, while also sheds light on the investigation of layered thermoelectric materials.

Calculation of the Activation Energy of Electrical ε2‐Conductivity of Weakly Compensated Semiconductors

A model of tunneling (jumping) migration of charge carriers near their mobility edge in the upper band of neutral states of majority hydrogen‐like impurities is proposed to calculate the energy of thermal activation of electrical ‐conductivity of weakly compensated semiconductors. The difference from the known Hubbard model consists in the scheme of interimpurity transitions of charge carriers and in the method of calculating the position of their tunnel mobility edge. The drift mobility edge of free charge carriers corresponds to the thermal ionization energy of majority impurities , which is located near the c‐band bottom or the v‐band top in n‐ and p‐type semiconductors, respectively, and is due to the overlap of excited states of electrically neutral majority impurities. The position of the tunnel mobility edge for ‐conductivity is determined by taking into account the Coulomb interaction of the majority impurities in the charge states and . It is assumed that doping and compensating impurities form a single simple nonstoichiometric cubic lattice in a crystal matrix. The calculations of the activation energy on the insulator side of the insulator–metal concentration phase transition for weakly compensated p‐Si:B, n‐Si:P, and n‐Ge:Sb crystals quantitatively agree with known experimental data.

Charge carrier transport in PbS films doped with iodine.

The results of the measurements of electrical and Hall resistivities on polycrystalline PbS films doped with iodine obtained through hydrochemical deposition are presented. The analysis of the temperature dependence of resistivity points out the crossover from the hopping mechanism due to thermal delocalization in the impurity band to the variable range hopping mechanism. The increase in the iodine content in the films leads to an increase in the impurity ionization energy. It has been established that the temperature dependence of resistivity over a wide temperature range obeys the inverse Arrhenius law, which is characteristic of disordered polycrystalline films with different sizes and orientations of crystallites relative to the substrate, as confirmed by AFM topography, Raman spectra and X-ray diffraction measurements. We found that the type of charge carrier changes from electrons to holes with an increase in the iodine content. Additionally, for a wide range of iodine doping, the concentration of charge carriers is low, indicating the possible occurrence of a self-compensation mechanism due to the formation of impurity defects.

Characterization of boron-doped single-crystal diamond by electrophysical methods (review)

A critical analysis of the existing methods of controlling the concentration of impurity and majority charge carriers in wide bandgap semiconductors and the issues of improvement of modern diagnostics of the main electrophysical properties of single-crystal diamond are considered based on the results of our studies and the works of other authors. It was found that independent assessment of impurity concentration and concentration of free charge carriers is of fundamental importance for semiconductor diamond due to very low (less than 1%) degree of ionization of the introduced impurity. The advantages and prospects of admittance spectroscopy as a diagnostic method for ultrawide bandgap semiconductors are shown and solutions aimed at the correct interpretation of the experimental data are proposed. The high ionization energy of boron impurity in diamond (370 meV) results in a strong frequency dispersion of the measured barrier capacitance. It is shown that under disturbance of quasi-static conditions in capacitance-voltage measurements, low frequencies and high temperatures should be used for correct assessment of the charge carrier concentration. The results of electrophysical studies are compared with traditional measurements of impurity concentration in diamond by optical methods. A decrease of hole activation energy from the boron impurity level from 325 to 100 meV was found upon increasing the boron concentration NA from 2·1016 to 4·1019 cm-3. The transition to the hopping mechanism of conductivity within the impurity (acceptor) band with thermal activation energy of 10-20 meV was registered for NA≥5·1018 cm-3 at temperatures of 120-150 K. Keywords: single-crystal diamond, boron impurity, charge carrier concentration, activation energy, admittance spectroscopy, capacitance-voltage measurements.

Growth and characterization of IR nonlinear optical PbIn6Te10 crystal

The crack-free PbIn6Te10 single crystal with ϕ28 mm × 90 mm was grown by the modified Vertical Bridgman method. Experimental results show that the main body of the boule is a PbIn6Te10 single crystal, while the tail has a certain amount of PbTe and Te. The measurements of UV and IR transmission demonstrate that the transmittance of PbIn6Te10 in 3.5–5.0 µm and 8–12 µm is more than 57 % and the corresponding absorption coefficient is in the range of 0.1–0.3 cm−1. The electrical properties of PbIn6Te10 crystal were studied within 50–300 K by temperature-dependent Hall-effect measurement. It is found that the as-grown crystal is an N-type semiconductor, and the carrier concentration varies nearly exponentially duo to the donor impurity ionization in the measured temperature range. Furthermore, the donor impurity ionization energy ∇ED was evaluated to be 0.04779 eV, and the fitted carrier mobility μH ∝ T−3/2 reveals the primary scattering mechanism within 170–300 K is the lattice vibration scattering.

Prospects for practical use of kaminskii thermovoltaic effect

The effect discovered by Kaminskii V. V. in 1999 represents one of the new principles of transformation of thermal energy into electrical energy. It was observed in samarium monosulfide, the results of investigation of the tensorresistive effect in which were presented at the 1st CP-CPLP. The tensorresistive sensitivity was maximum among all semiconductors. Qualitative theoretical analysis of the formidable properties of SmS is made from the relations between ionization energy of impurities and ionization potentials and ionic radii, which are more favorable in rare earth elements. This is explained by the presence in the atoms of the 4-f electronic layers, which have the maximum electron density. This exclusivity determines the most rational area of practical applications of rare-earth semiconductors in quality of sensitive elements of transducers of physical quantities of resistive type. In the thermovoltaic effect, the samples located in the temperature field without gradient generate the electromotive force. The nature of the effect is related to the variation of the valence of Sm ions and the gradient of the concentration of impurities in the samples. The comparison of the parameters of Kaminskii's effect and Seebek's classical thermoelectric effect is given. Between them, the maximum values of the thermoelectric yield are 36% and 10%, respectively. The thermovoltaic effect, by virtue of its energy efficiency, absence of the need for the creation of the temperature gradient in the working element of the transducer, ecological purity and the possibility of the use of the unspecialized secondary thermal energy sources, has high prospects for practical use. The obtained results are explained by the fundamental causes related to the position of rare earth elements in Mendeleev's periodic table of elements.

Maximum hopping direct current conductivity via hydrogen-like impurities in semiconductors

A quasi-classical model for calculating DC (direct current) electrical conductivity in crystalline semiconductors with hydrogen-like impurities is developed at the transition from band conduction to impurity hopping conduction with decreasing temperature. This transition from the minimum band conductivity to the maximum hopping conductivity via impurities has the form of a characteristic "kink" in the temperature dependence of the electrical resistivity. The idea of the calculation is to preliminarily determine the transition temperature Tj using the standard approach within the framework of the two-band model. The shift of the top of the v-band (the bottom of the c-band) into the depth of the band gap due to the formation of a quasi-continuous band of allowed energy values from the excited states of acceptors (donors) is taken into account. This leads to a decrease in the value of a thermal ionization energy of the majority shallow impurities due to a decrease in the maximum localization radius of a hole on an acceptor (an electron on a donor) with increasing impurity concentration. The values of the observed maximum hopping conductivity and drift hopping mobility corresponding to the temperature Tj are calculated. The numerical calculation within the framework of the proposed model is consistent with the known experimental data on the electrical conductivity and Hall coefficient of moderately compensated p-Ge crystals doped by neutron transmutation and non-intentionally compensated metallurgically doped n-Ge, as well as n- and p-Si crystals on the insulator side of the Mott insulator--metal concentration phase transition. Keywords: bulk crystals of germanium and silicon, hydrogen-like acceptors and donors, holes and electrons, band and hopping motion of charge carriers.

Piezoresistive Thermal Characteristics of Aluminum-Doped P-Type 3C-Silicon Carbides

This study examined the temperature-related piezoresistance issues of p-type doped 3C-silicon carbide (3C-SiC) materials. Previously, we proposed piezoresistance temperature models that describe phenomena based on the ionization energies of materials oriented for high-temperature operations. This study aimed to determine the ionization energy as a function of the aluminum doping concentration of 3C-SiC. However, at the low-temperature region a drastic decrease in the piezoresistive coefficient was observed, and it was predicted to occur when materials possessing large impurity ionization energy are used under negative thermal strained conditions. This phenomenon is in contrast to the conventional piezoresistance factor P(N,T) that is based on narrow band-gap materials such as silicon or germanium; thus, it provides new insights into low-temperature piezoresistance phenomena.

Thermal ionization energy of hydrogen-like impurities in semiconductor materials

In the work the dependence of the thermal ionization energy of hydrogen-like donors and acceptors on their concentration in n- and p-type semiconductors is analyzed analytically and numerically. The impurity concentrations and temperatures at which the semiconductors are on the insulator side of the concentration insulator – metal phase transition (Mott transition) are considered. It is assumed that impurities in the crystal are distributed randomly (according to Poisson), and their energy levels are distributed normally (according to Gauss). In the quasi-classical approximation, it is shown, for the first time, that the decrease in the ionization energy of impurities mainly occurs due to the joint manifestation of two reasons. Firstly, from the excited states of electrically neutral impurities, a quasicontinuous band of allowed energy values is formed for c-band electrons in an n-type crystal (or for v-band holes in a p-type crystal). This reduces the energy required for the thermally activated transition of electron from the donor to the c-band (for the transition of the hole from the acceptor to the v-band). Secondly, from the ground (unexcited) states of impurities a classical impurity band is formed, the width of which at low temperatures is determined only by the concentration of impurity ions. In moderately compensated semiconductors (when the ratio of the concentration of minority impurities to the concentration of majority impurities is less than 50 %) the Fermi level is located closer to the edge of the band of allowed energy values than the middle of the impurity band, that issue reduces thermal ionization energy of impurities from states in the vicinity of the Fermi level (transition of electron from a donor to the c-band, or hole from an acceptor to the v-band). Previously, these two causes of decrease in the thermal ionization energy due to increase in the concentration of impurities were considered separately. The results of calculations according to the proposed formulas are quantitatively agree with the known experimental data for a number of semiconductor materials (germanium, silicon, diamond, gallium arsenide and phosphide, silicon carbide, zinc selenide) with a moderate compensation ratio.

Thermal ionization energy of hydrogen-like impurities in semiconductor materials

Thermal ionization energy of hydrogen-like impurities in semiconductor materials

Temperature dependence of diamond MOSFET transport properties

The electrical properties of p-channel diamond metal-oxide-semiconductor FETs (MOSFETs) have been investigated for temperatures ranging from 6.5 K to 673 K. Diamond MOSFETs exhibit typical normally-off MOSFET features from 6.5 K to 623 K. Despite the high impurity ionization energy in diamond (donor: 0.58 eV, acceptor: 0.38 eV), an inversion channel is formed in diamond MOSFETs at low temperature (up to 6.5 K). Moreover, the high-temperature measurements induce an irreversible shift in the threshold voltage of diamond MOSFETs (from −6.5 V to −3.15 V), leading to a significant improvement of the room temperature drain current. The threshold voltage shift results from a reduction of the total density of the extrinsic charges at Al2O3/diamond interface because of unintentional post-deposition annealing of the Al2O3 gate oxide at high temperature.

Calculation of band structure of the strained germanium nanofilm, doped with a donor impurity

Abstract The band structure of the doped germanium nanofilm grown on the G e ( x ) S i ( 1 − x ) (001) substrate was calculated on the basis of the theory of deformation potential. It was shown that internal mechanical strains exceeding 2% arise in the germanium nanofilm with increasing S i content in the substrate. The presence of such strains leads to the ( L 1 − Δ 1 ) type inversion of the absolute conduction band minimum of the nanofilm. As a result of such radical reconstruction of germanium band structure under deformation, the ionization energy of the donor dopant in the nanofilm is increasing which is explained by the increase of the effective mass of electron and, accordingly, the decrease of the characteristic size of the wave function of electron that is localized on the donor impurity. The dependence of the ionization energy of impurity on the magnitude of the internal strains is due to different values of the baric coefficients of the shift of the energy level of impurity and of the lowest conduction band minimum of the nanofilm. Obtained results can be used in design and modeling of electronic devices and sensors for modern nanoelectronics with pre-set operating characteristics on the basis of strained germanium nanofilm doped with various donors.

Quantum transport relating to impurity quantum dots in silicon nanostructure transistor

As the characteristic size of the transistor approaches to its physical limit, the effect of impurities on device performance becomes more and more significant. The number of impurities and the range of impurity fluctuation become very limited in channel space less than 10 nm, and ionized impurities in local nano-space can even exhibit quantum dot characteristics, providing two discrete levels for charge transport. The behaviour of carrier tunnelling through quantum dots induced by ionized impurities can reveal the abundant quantum information, such as impurity ionization energy, coulomb interaction energy, electron activation energy, orbital level filling, and spin of local electrons. Quantum transport properties are also different in different doping concentrations because whether the quantum states overlap depends on the impurity atom spacing. The silicon nanostructure transistors using impurity atoms as building blocks of quantum transport are also called dopant atom transistors, which are not only compatible with complementary metal oxide semiconductor (CMOS) technology, but also expected to be the basic components of quantum computing circuits in the future. So far, their operating temperature is relatively low due to the shallow ground state energy level of impurity atoms. It is of great significance to study the quantum transport properties in dopant atom transistors and to observe quantum effects among them at room temperature. In this article, the quantum transport properties in single, discrete and coupled impurity atomic systems are described in detail by combining Anderson localization theory and Hubbard band model. Quantum transport in a discrete impurity atomic system is not only controlled by gate voltage, but also dependent on temperature. The current transport spectrum in the coupled impurity atomic system reveals more complex quantum dot characteristics. Single atom transistor can regulate quantum transport only by one impurity atom, which represents the ultimate scale limit of solid state devices. In addition, the methods of improving the operating temperature of dopant atom transistors are also systematically introduced, thereby laying a foundation for their practical applications.

Bubble states of atoms in liquid helium

The solvation of impurity atoms {Na, K, Rb, Cs, Mg, Ca, Sr, Ba} with small ionization energy in liquid helium is studied. It is shown that allowance for unmatched interaction of impurity atoms and helium atoms is important for determining the parameters of the atomic state. The size of the bubble state R0 is determined by the strong repulsion between helium atoms and valence electrons of impurity atoms. The R0 value is universal, and the expression 2R0/ν = const ≈ 11–13 depends weakly on the place of the impurity atom in the periodic table. The parameter ν is given by the impurity ionization energy J = 1/2ν2 (in atomic units); the ν value indicates the size of the impurity atom. An energy barrier that separates the bulk and surface atomic impurity states is determined.

How to characterize capacitance of organic optoelectronic devices accurately**Project supported by the Fundamental Research Funds for the Central Universities, China

The selection of circuit model (i.e., parallel or series model) is critical when using a capacitance–frequency and capacitance–voltage technique to probe properties of organic materials and physical processes of organic optoelectronic devices. In the present work, capacitances of ITO/Alq3/Al and ITO/CuPc/Al are characterized by series and parallel model, respectively. It is found that the large series resistance comes from the ITO electrode and results in the inapplicability of the parallel model to measuring the capacitances of organic devices at high frequencies. An equivalent circuit model with consideration of the parasitical inductance of cables is constructed to derive the capacitance, and actual capacitance–frequency spectra of Alq3 and CuPc devices are obtained. Further investigation of temperature-dependent capacitance–frequency and capacitance–voltage characteristics indicates that CuPc and Al form the Schottky contact, the density and ionization energy of impurities in CuPc are obtained. Moreover, more practical guidelines for accurate capacitance measurement are introduced instead of the impedance magnitude, which will be very helpful for the organic community to investigate capacitance-related characteristics when dealing with various organic optoelectronic devices.

Effects of impurity size and heavy doping on energy-band-structure parameters of various impurity-Si systems

The effects of impurity size and heavy doping on energy-band-structure parameters of various donor (or acceptor)-Si systems were investigated. A satisfactory description was obtained for intrinsic properties such as: the effective dielectric constant, effective impurity ionization energy, effective intrinsic band gap, being doping-independent, and critical impurity density, Ncn(cp)GMM, which is derived from our simple generalized Mott model (GMM), as well as for extrinsic properties such as: the Fermi energy, reduced band gap, optical band gap, being doping-dependent, and critical impurity density, Ncn(cp)SSS, which is determined by our complicated spin-susceptibility-singularity (SSS) method. That gives: Ncn(cp)SSS≡Ncn(cp)GMM for all the studied donor (or acceptor)-Si systems.

Electrical properties of diluted n- and p-Si1 − x Ge x at small x

Hall effect and conductivity measurements are taken on Si1 − x Ge x of n- and p-type at x ≤ 0.05. Much attention is given to electrical measurements over a temperature interval of 25 to 40 K where the mobility of charged carriers is strongly affected by alloy scattering. The partial mobility of electrons and holes due to this scattering mechanism is estimated for n-Si1 − x Ge x and p-Si1 − x Ge x at small x. Together with this, an effect of the presence of Ge atoms upon the ionization energy of phosphorus and boron impurities is investigated. Some points related to an inhomogeneous distribution of Ge atoms in Si1 − x Ge x are discussed.

Effects of Coulomb Impurity in Semiconductor Nanowire

ABSTRACTWe present calculation of electronic structure of impurity in nanowire. Ionization energy of impurities are calculated in dependence on nanowire radius. Direct Hamiltonian matrix diagonalization method with the physically reasonable approximate potential is employed for finding the exact solution of Schrödinger equation in the effective-mass approximation. It is shown that shallow donors are strongly influences by space confinement, which is expressed in sharp increase of ionization energy. Calculations show that effect of space confinement on deep impurities is less pronounced. The obtained results give hope that by selecting optimal value of nanowire radius compensation processes can be suppressed.

Non-ohmic hopping conduction of a diode base extracted from the diode current-voltage characteristics

Using the method of extracting a series resistance from a p- n diode current-voltage characteristics developed earlier, parameters of low-temperature non-ohmic conduction in bases of two types of silicon diodes have been studied. In the diode of the first type, with finite value of impurity ionization energy, low-temperature impurity breakdown in the diode base is accompanied by hysteresis of its conduction; in the diode of the second type, the impurity breakdown occurs in soft form. In the pre-breakdown region, the results obtained for the diodes of both types, agree completely with existing picture of non-ohmic hopping conduction in spite of significant space inhomogeneity of the diode structures and non-equilibrium character of the transport in them. In the post-breakdown region, the certain peculiarities are available. For the first time the activationless hopping conduction has been revealed in crystalline silicon.

Microstructure and Transport Properties in Alloyed Ohmic Contacts to P-Type SiC and GaN for Power Devices Applications

The formation of good Ohmic contacts to p-type silicon carbide (SiC) and gallium nitride (GaN) is an important physical and technological concern, because of the difficulty to find metals with low Schottky barriers to p-type wide band gap materials, and due to the high ionization energies of p-type dopant impurities. Typically, to overcome these issues, alloyed metallic compounds are used. In this work, the electrical properties of alloyed Ohmic contacts to p-type (Al-implanted) 4H-SiC and p-type (Mg-doped epilayers) GaN are presented and correlated with their microstructure. The impact of the surface preparation and annealing conditions are discussed, reporting the cases of Al/Ti contacts to p-SiC and Au/Ni contacts to p-GaN. The electrical characterization as a function of temperature allowed to define the dominant transport mechanism and to determine the barrier heights.