Ionization Of Impurity Centers Research Articles

Conductivity of Semiconductor Single-Walled Carbon Nanotubes with Allowance for the Ionization of Impurity Centers

Conductivity of Semiconductor Single-Walled Carbon Nanotubes with Allowance for the Ionization of Impurity Centers

Some thermophysical properties of (In2Te3)1 − x(Cd0.9Zn0.1Te)x solid solutions

Temperature dependences of total thermal conductivity and certain thermomagnetic coefficients of (In2Te3)1 − x(Cd0.9Zn0.1Te)x solid solution alloys (x = 0.01 and 0.03) were investigated and phonon scattering mechanisms were established. It was shown that ionized impurity centers and point structural defects are active in heat transfer at low temperatures, and scattering by acoustic and optical phonons dominates at high temperatures. At high temperatures, an additional thermal resistance of the crystal lattice appears in the studied solid solution, leading to a three-phonon scattering mechanism. A change in the thermomagnetic coefficients with temperature indicates a variable mechanism of phonon scattering and the elastic character of electron scattering in (In2Te3)1 − x(Cd0.9Zn0.1Te)x alloys.

Intersubband optical absorption in GaAs parabolic quantum well due to scattering by ionized impurity centers, acoustical and optical phonons

The intersubband absorption linewidth dependence on well width in GaAs quantum well is calculated. Three mechanisms of scattering have been discussed there: carriers scattering by optical (LO), acoustic (LA) phonons and ionized impurity centers (ION). The method which used for calculations is similar to a well-known method of calculating transport mobility. The estimation for absorption coefficient is proposed, based on two-dimensional dynamical conductivity expression. The LO phonon emission process is activated starting from some quantum well (QW) width so it has its impact on absorption linewidth.

Free-carrier absorption in a parabolic quantum well with consideration of scattering on ionized impurities

Intra-subband transitions caused by light absorption in a parabolic quantum well is considered taking into account the scattering by ionized impurity centers. To calculate the scattering matrix element, the Born approximation is used and the interaction with the impurity is described by the Coulomb potential. An analytical expression for the absorption coefficient of processes with the initial absorption of photon and further scattering by an ionized impurity center is obtained. For absorption coefficient the frequency characteristics and dependence on the width of quantum well are examined.

Free carrier absorption in quantum well in consideration of the interaction with impurities

Intrasubband transitions caused by light absorption in a parabolic quantum well is considered taking into account the scattering by ionized impurity centers. To calculate the scattering matrix element Born approximation is used, and the interaction with the impurity is discribed via screened Coulomb potential. An analytical expression for the absorption coefficient is obtained based on the the initial absorption of a photon and a further scattering on ionized impurity center. Absorption coefficient frequency characteristics and dependence on the width of the quantum well is examined.

Temperature Dependence of Electrical Characterization in n+ - CdS/ p - CdTe Thin Film Solar Cells – Study of Shallow/Deep Defects

ABSTRACTFor CdTe there is no real distinction between defects and impurities exists when non-shallow dopants are used. These dopants act as beneficial impurities or detrimental carrier trapping centers. Unlike Si, the common assumption that the trap energy level Et is around the middle of the band-gap Ei, is not valid for thin film CdTe. Trap energy levels in CdTe band-gap can distributed with wide range of energy levels above EF. To identify the real role of traps and dopants that limit the solar cell efficiency, a series of samples were investigated in thin film n+-CdS/p-CdTe solar cell, made with evaporated Cu as a primary back contact. It is well known that process temperatures and defect distribution are highly related. This work investigates these shallow level impurities by using temperature dependent current-voltage (I-V-T) and temperature dependent capacitance-voltage (C-V-T) measurements. I-V-T and C-V-T measurements indicate that a large concentration of defects is located in the depletion region. It further suggests that while modest amounts of Cu enhance the cell performance by improving the back contact to CdTe, the high temperature (greater than ∼100°C) process condition degrade device quality and reduce the solar cell efficiency. This is possibly because of the well-established Cu diffusion from the back contact into CdTe. Hence, measurements were performed at lower temperatures (T = 150K to 350K). The observed traps are due to the thermal ionization of impurity centers located in the depletion region of p-CdTe/n+-CdS junction. For our n+-CdS/p-CdTe thin film solar cells, hole traps were observed that are verified by both the measurement techniques. These levels are identical to the observed trap levels by other characterization techniques.

Synthesis of tellurium nanotubes by galvanic displacement

Tellurium nanotubes with controlled diameter and wall thickness were synthesized by galvanic displacement of cobalt nanowires and their temperature dependent field effect transistor and magnetoresistance properties were systematically investigated. The nanotube diameter was slightly larger than the sacrificial cobalt nanowire diameter with a wall thickness of range from 15 to 30 nm depending on the diameter of cobalt nanowires. Te nanotubes show p-type semiconducting property with the field effect carrier mobility of approx. 0.01 cm 2/V s which is relatively lower than other 1D nanostructure. Low mobility might be attributed to porous morphology with small grain size (<10 nm). Temperature dependent mobility also exhibiting a Conwell–Weisskopf relationship to temperatures below 250 K, indicating that the dominant scattering sites are ionized impurity centers. Unique MR behavior was observed from nanotube with a maximum magnetoresistance ratio of 37% at 260 K.

Mobility of two-dimensional electrons upon scattering by a correlated distribution of impurity ions

Correlation effects in the mobility of two-dimensional electrons upon scattering by a correlated distribution of impurity ions are described in the framework of the hard-sphere model. The theory is developed for the case of partially ionized impurity centers when correlations in the distribution of impurity ions are weakened as the result of a deficit of free positions for impurity holes. The calculations are performed for heterostructures with a wide spacer when small-angle scattering of electrons dominates.

Simulation of avalanche multiplication of electrons in photodetectors with blocked hopping conduction

The avalanche electron multiplication in a silicon structure with blocked hopping conduction is simulated for the photon-counting mode. The acceleration of an electron in an electric field that is linearly dependent on the coordinate, the elastic scattering of electrons by longitudinal acoustic phonons, the inelastic scattering of electrons by intervalley phonons, and the ionization of impurity centers are taken into account when considering the motion of an electron. A simple algorithm making it possible to calculate directly the coordinates of all ionized centers in an avalanche and the probability of N electrons leaving the avalanche if a single electron has entered the multiplication region is suggested. It is shown that this probability is at its maximum in the vicinity of 〈N〉 (the mean value of the leaving-probability function), which is consistent with experimental data.

Photoionization related phenomena in doped insulators: The role of inversion site symmetry of impurity centers

The light induced ionization of impurity centers and defects in insulating crystals results in many phenomena such as charge transfer optical transitions in absorption spectra, photoconductivity, the photovoltaic effect, optical bleaching, and photochemical persistent spectral hole burning. This paper considers specific effects in photoionization related phenomena which are closely connected with inversion symmetry of impurity centers. These recently observed effects include (a) the drastic dependence of the photoionization energy on impurity sites lacking inversion symmetry (Li2Ge7O15:Cr3+), (b) the direct dependence of the sign of the photovoltaic effect on the polarity of impurity sites in doped pyroelectric crystals (LiNbO3:Cr3+), and (c) the anomalous broadening of photochemical persistent spectral holes in zero-phonon spectra of inversionless impurity centers (CaS:Eu).

Thermal ionization of impurity centers in Fe-doped Bi12SiO20 and Bi12GeO20 crystals

The spectral and temperature dependence of the optical absorption and thermally stimulated depolarization currents in Fe-doped Bi12SiO20 and Bi12GeO20 crystals are investigated in the photon energy range 1.36–3.46 eV and temperature 85–750 K. The results show thermally induced electron redistribution between donor and acceptor levels and defect association-dissociation processes and are discussed using the configuration-coordinate model.

Ionization of impurity centers in a semiconductor quantum superlattice by nonlinear electromagnetic waves

The ionization of impurity centers in a semiconductor superlattice by nonlinear electromagnetic waves, which are the most general solution of the sine-Gordon equation and can be expressed in terms of the Jacobi elliptic functions, is investigated. The problem is solved in a quasiclassical approximation for arbitrary ratio of V (depth of the impurity energy level) and Δ (half-width of the conduction miniband). Results in agreement with those for solitary waves and sinusoidal (linear) electromagnetic waves are obtained in limiting cases. The effect of a uniform high-frequency electric field on the processes leading to the ionization of impurities by solitary waves is also investigated.

Drift of excitons in an inhomogeneous electric field in silicon at 4.2K

The results are presented of the experimental detection and investigation of the phenomenon of the drift of excitons in an inhomogeneous electric field. The investigations were performed on silicon structures with Shottky barriers at 4.2 K. A study was made of the influence of the photoexcitation intensity and electric field strength on the breakdown dynamics of the structure. The experimental results were used to show that breakdown of a reverse-biased Shottky barrier involves a narrowing of the width of the space-charge region due to a drift of excitons in the inhomogeneous electric field and to recombination of electrons on ionized impurity centers of the barrier.

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.

Electron entrainment by superlattice breezers with ionization of impurity centers

It has been shown earlier [1-3] that electromagnetic breezers can be propagated in a superlattice (SL) under certain conditions. One of the possible manifestations of the existence of breezers in an SL is that of free-carrier entrainment by the field of an isolated wave [2]. On the other hand, it is known that, along with free-carrier entrainment by photons in semiconductors, there exists an effect of electron entrainment in the ionization of impurity centers [4]. For this reason, it is important to study the effect of electron entrainment by bions in an SL in the process of impurity ionization as yet another manifestation of the existence of breezers in SLs. The principal cause of such entrainment is asymmetry in the probabilities of transitions of electrons from impurity centers to conduction minibands [4]. We shall assume that the energy spectrum of SL electrons is given by the relation

Zeeman electron mass anomaly in InP as determined from orbital and spin splitting of donor 2P levels using high-resolution photoluminescence spectroscopy

The effective mass of an electron in InP determined from Zeeman splittings of the donor 2P level shows a strong magnetic field dependence. This Zeeman effective mass is approximately 45% smaller than the cyclotron mass at low magnetic fields. This was deduced from both the orbital and spin splittings of the 2P donor levels. The magnetic field splittings were determined from radiative transitions resulting from collapse of donor bound excitons leaving the terminal state in an excited state. The magnitude of the effect is much larger than that previously observed in GaAs. This anomaly is qualitatively explained on the basis of level mixing resulting from random static electric fields present throughout the crystal due to ionized impurity centers. The mass obtained from the orbital splitting is in good agreement with that obtained from the spin splitting.

Electron-mass anomaly as determined from the Zeeman effect of the donor 2P levels in GaAs.

The effective mass of an electron determined from Zeeman splitting of the donor 2${\mathit{P}}_{\ifmmode\pm\else\textpm\fi{}1}$ levels in some GaAs crystals shows a strong magnetic-field dependence. The Zeeman effective mass reported in this paper is always greater than the cyclotron effective mass for all magnetic fields up to 40 kG. The Zeeman effective mass goes through a maximum at approximately 12 kG and tends toward the cyclotron effective mass at 40 kG. The Zeeman mass was deduced from both the orbital and spin splittings of the 2P donor levels. The magnetic-field splittings were determined from radiative transitions resulting from the collapse of a donor-bound exciton leaving the terminal state in an excited state. The magnitude of the effect is greater than that previously observed in GaAs and also is in the opposite direction, an increase rather than a decrease in mass. It is concluded that this anomaly could be explained on the basis of level mixing resulting from static electric fields present throughout the crystal due to ionized impurity centers. In the present case, the ionized impurity centers are not uniformly distributed throughout the crystal. Although there are some differences between the masses obtained from orbital splitting and the masses obtained from spin splitting, the shapes of the curves are quite similar.

InSe electrical characterization by means of transport parameters

SCLC measurements in single crystals of the layered semiconductor n-type InSe are reported. The measurements were carried out at various temperatures and on samples grown with indium added in excess (from 5 to 10%). The experimental results suggest that the trapping levels location and the charge transport are dependent on the indium excess. Only the samples grown with an indium excess of about 5% show the features typical of intrinsic semiconductors. The anomalous behaviour of samples grown with indium excess between 6 and 10 is explained by means of scattering mechanisms between charge carriers and ionized impurity centers.

Theory of ESR Line Width in n-Type InSb

Anisotropic spin-dependent energy \(\delta_{0}(E)\mathbf{\sigma\cdot\hat{\kappa}}(\mathbf{\hat{\kappa}}\sim{O}(k^{3}))\), σ : Pauli matrix), introduced by Rashba and Sheka in their study of the combined resonance in III-V compounds, provides a broadening of the Zeeman level. However, the level broadening is extremely narrowed by frequent scattering of the conduction electrons induced by ionized impurity centers. The present mechanism, together with the spin-flip processes related to the ionized impurity scattering and the LO-phonon exchange, gives a qualitative explanation for the observed ESR line width of the degenerate samples in n-InSb.

The electrical conductivity of solid solutions of TiO2 in ?-Al2O3 as a function of the partial oxygen pressure

An investigation was carried out of the electron conductivity as a function of the partial oxygen pressure of solid solutions of TiO2 inα-Al2O3 over the temperature range 1100–1400°C at low partial oxygen pressures (10−8−10−18 atm). Up to 1100°C the predominant types of defect are once only ionized impurity centers Ti+(Al) and electrons in the conductivity zone. At higher temperatures the main type of defect takes the form of once only ionized impurity centers, oxygen vacancies, and electrons in the conductivity zone.