Multiphonon ionization of deep centers in amorphous silicon nitride: Experiment and numerical simulations

The conductivity of amorphous silicon nitride has been studied experimentally in a wide range of electric fields and temperatures. The experimental results are in a quantitative agreement with the theory of multiphonon ionization of deep centers for the bipolar model of conductivity. The best agreement between experiment and the calculation has been obtained for the same parameters of deep electron and hole centers.     

Photofield ionization of deep centers in semiconductors,taking Coulomb-field effects into account

The electrical-absorption coefficient in semiconductors is calculated for the case of charge-carrier transition from a deep level to the closest level at the base of a Hulthen model potential, including both short-range and long-range (Coulomb) components. The effect of the Coulomb field on the electron wave function in the conduction band is taken into account.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 85–91, December, 1977.     

Multiphonon hopping in disordered semiconductors

Equations of motion for the nonequilibrium single-frequency density matrix are used to obtain a balance equation describing the kinetics of electron hopping between localized states in disordered semiconductors. Conclusions are drawn about the applicability of the theory of multiphonon processes to systems with a small nonadiabaticity. The decoupling used is a generalization of one used earlier to the multiphonon case. The balance equation found in the Markov approximation for the average number of sites occupied in an electric field contains the field dependence of the multiphonon-transition probability, tending to the well-known weak-field limit.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No.2, pp.35–42, February, 1976.In conclusion the author is grateful to V. L. Bonch-Bruevich and A. G. Mironov for discussing this work.     

Calculation of local vibrations at deep centers in semiconductors

A theoretical treatment of local vibrational modes applied to intrinsic defects in GaAs is presented. The dynamics of the perfect and imperfect lattice are described with the help of the valence force model of Kane and the Coulomb interaction is included explicitly. The interatomic forces of the host crystal and at the defect are determined by using the self-consistent density functional theory applied to a supercell containing 54 atoms. The force constants due to various displacements of the nearest neighbours of an atom are used to determine the valence force parameters. They are used to calculate the dynamical matrix of the perfect crystal from which we obtain the phonon dispersions curves. They are in good agreement with the experiments. In case of a defect we calculate the dynamical matrix of 280 vibrating atoms around the defect and determine the local vibrational modes and resonances and their spatial extent in both optical and acoustical branches of the crystal phonons. The results for the As-antisite and the vacancies in GaAs are compared with Raman scattering and optical absorption experiments at intrinsic defects in GaAs. The formation entropies of these defects are also calculated.     

Multiphoton mechanism of ionization of deep centers in HfO2

The charge transfer mechanism in HfO₂ has been studied theoretically over wide ranges of electric fields and temperatures. The calculations based on the theory of multiphoton ionization of deep centers agree with experimental data.     

Multiphonon processes in nuclear relaxation via paramagnetic centers

We investigate the role of Orbach-Aminov multistage phonon processes in nuclear spin-lattice relaxation via paramagnetic centers for ions with 1/2 spin in the absence of splitting by the crystal field.Lenin State Pedagogical University, Moscow. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, No. 10, pp. 1071–1076, October, 1995.     

Effect of a magnetic field on thermally activated tunneling ionization of impurity centers in semiconductors

An expression for the probability of thermally activated tunneling ionization in an electric field in the presence of a magnetic field is obtained. It is shown that the logarithm of the ionization probability is proportional to the squared electric field, and the coefficient of proportionality decreases with increasing magnetic field. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 10, 763–767 (25 November 1998)     

Muonium defect centers in semiconductors

After a brief summary of the properties of the muonium defect centers observed in the elemental group IV semiconductors, the status of studies of muonium centers in semiconductors at the time of the last μSR conference in 1983 will be compared with what is currently known. With the introduction of new experimental techniques, such as high-transverse-field μSR and level-crossing spectroscopy, many new results are or soon will be available on muonium centers. These, combined with new theoretical studies, should lead to rapidly increased insight into a subject which has been both puzzling and resistant to clarification.     

A case for large Auger recombination cross sections associated with deep centers in semiconductors

It is argued that the recent quantitative results concerning localized defects in semiconductors (e.g. GaAs) are consistent with the possibility of large Auger-type cross sections associated with recombination at these centers.It is proposed that many of the capture cross sections reported to be in the range 10^?13–10^?16cm², which exhibit only weak temperature dependence, and which do not depend on carrier concentration, might be explained by this mechanism.     

Effect of a magnetic field on thermally stimulated ionization of impurity centers in semiconductors by submillimeter radiation

The probability of electron tunneling from a bound state into a free state in crossed ac electric and dc magnetic fields is calculated in the quasiclassical approximation. It is shown that a magnetic field decreases the electron tunneling probability. This decreases the probability of thermally activated ionization of deep impurity centers by submillimeter radiation. The logarithm of the ionization probability is a linear function of the squared amplitude of the electric field and increases rapidly with the frequency of the electric field.     

On the determination of thermal ionization energy of deep centers from ESR data

It is shown that the skin effect due to thermal generation of free carriers may affect the ESR signal more than deep center depopulation. Experimental results for 0.33 eV deep Eu²⁺ donor in CdF₂ crystals are presented, to show the way in which the thermal energy of deep centers is deduced from the ESR data.     

Optical absorption involving hydrogen-like centers in semiconductors

Russian Physics Journal -     

Intrinsic DX centers in ternary chalcopyrite semiconductors

In III-V and II-VI semiconductors, certain nominally electron-donating impurities do not release electrons but instead form deep electron-traps known as "DX centers." While in these compounds, such traps occur only after the introduction of foreign impurity atoms, we find from first-principles calculations that in ternary I-III-VI2 chalcopyrites like CuInSe2 and CuGaSe2, DX-like centers can develop without the presence of any extrinsic impurities. These intrinsic DX centers are suggested as a cause of the difficulties to maintain high efficiencies in CuInSe2-based thin-film solar-cells when the band gap is increased by addition of Ga.     

Paramagnetic centers in neutron irradiated glassy semiconductors

EPR was used for investigation of neutron irradiated glassy semiconductors (E_n = 2 MeV). It was shown that the neutron irradiation causes an increased number of unpaired spins: EPR signal was detected in glassy semiconductors which have not exhibited any signal before irradiation. A possible interpretation of the formation of paramagnetic centers due to neutron irradiation is suggested.     

Optical spectroscopy of single impurity centers in semiconductors

Using optical spectroscopy with diffraction limited spatial resolution, the possibility of measuring the luminescence from single impurity centers in a semiconductor is demonstrated. Selectively studying individual centers that are formed by two neighboring nitrogen atoms in GaAs makes it possible to unveil their otherwise concealed polarization anisotropy, analyze their selection rules, identify their particular configuration, map their spatial distribution, and demonstrate the presence of a diversity of local environments. Circumventing the limitation imposed by ensemble averaging and the ability to discriminate the individual electronic responses from discrete emitters provides an unprecedented perspective on the nanoscience of impurities.     

Field-enhanced carrier-generation effect of deep-level centers in semiconductors

A general theory on the field-enhanced carrier generation of deep-level centers in semiconductors is put forward in order to explain the relevant phenomena observed in some experiments. It is concluded that generally both the Coulombic and the non-Coulombic emissions control the generation process of carriers from deep-level centers. On the basis of this, a theoretical relationship between the generation current density and the effective generating width is derived. Further it is shown that the present theory is better than the previous ones in which the non-Coulombic emission was ignored in explaining the experimental results and the latter can be considered a special case of the former.     

Impact ionization rate in direct gap semiconductors

In the framework of the 14-band k ? p model, the intensity of the impact ionization processes in direct gap semiconductors is studied and explicit expressions for the impact ionization rate are obtained. It is shown that the rate of the process near the threshold energy is determined by the sum of the isotropic and strongly anisotropic contributions. The former contribution is proportional to the cube of the distance from the threshold, whereas the latter is a quadratic one arising only because of the coupling with remote bands. The comparison of these contributions under averaging over the nondegenerate isotropic distribution of nonequilibrium electrons characterized by some effective temperature T* demonstrates that the cubic contribution rather than the commonly used quadratic one is dominant in the direct gap semiconductors with E _g<1?1.5 eV up to T* = 300 K. This should be taken into account in the calculations of the operating characteristics of the devices based on the avalanche multiplication of charge carriers.     

Express methods of determining the parameters of deep centers in semiconductors from the data of nonsteady capacitive spectroscopy

Journal of Applied Spectroscopy -