Nonlinear response and chaos in semiconductors induced by impact ionization

A review is given of the nonlinear response and chaos induced by impact ionization of neutral shallow donors, observed in n-GaAs. Two kinds of the observation are described; (i) firing wave instability, and (ii) periodically driven current filament. For the firing wave instability, several important aspects are discussed including the selective excitation of the current filaments and the deterministic nature of the firing density wave. The nonlinear response of a periodically driven current filament has been investigated by applying a dc+ac bias of the form ofV _dc+V _ac sin(2f ₀ t), wheref ₀1 MHz. The carrier dynamics and the bifurcation routes to chaos are discussed in terms of the observed phase diagram and the bifurcation map. The deterministic nature of the strange attractors are described in detail in terms of the correlation dimension and the Kolmogorov entropy.     

A negative differential conductivity due to recombination and impact ionization in semiconductors at low temperatures

The probability of impact ionization and the recombination time are known to increase monotonically with the electric fieldE. I show that at low temperatures both functions achieve a maximum and decrease in the electric field range where the emission of optical phonons with subsequent impurity scattering dominate. This nonmonotonicity results in three different types of N-shaped negative differential conductivity (n-ndc). The carrier concentration and the current decrease whenE increases due to decreasing of the impact ionization probability for weakly compensated samples and of the recombination time for highly compensated samples. At the antithreshold electric-field impact ionization dies out, which results in a dramatic decrease of the current for intermediately compensated samples. This huge n-ndc could be used in a novel type of the Gunn diode. The essential increase of threshold electric field of impact ionization is also predicted, and the effect could enhance the efficiency of photodetectors.The research was supported by the Alexandervon-Humboldt-Foundation     

Photoreflectance of indium antimonide

The photoreflectance spectra of n-InSb layers were measured using photomodulation Fourier transform infrared spectroscopy. The samples were grown by molecular beam epitaxy on heavily doped n ⁺-InSb(001) substrates annealed under different conditions. The strength of the near-surface electric field was determined from the period of the Franz–Keldysh oscillations observed in the photoreflectance spectra. It was noted that the strength of the electric field increases during a long-term storage of the samples in air. The treatment of n-InSb layers in a 1M aqueous solution of Na₂S led to an increase in the measured field. Previously, it was shown that, after this treatment, the surface Fermi level is shifted deep into the conduction band and, probably, does not depend on the conditions and time of the preliminary storage of the samples. With the use of passivation in Na₂S, the optical method developed in this study allows for the contactless measurement of the concentration of electrons in n-InSb homoepitaxial layers.     

Inversion channel conductivity in indium antimonide

The conduction characteristics of the channel of a metal-oxide-silicon field effect transistor (MOSFET) are calculated with consideration of the effect of the charge of surface states and mobile carriers in the inversion layer. The relationships obtained are presented in the form of simple analytic expressions. Using this calculation a method is developed for determination of surface state parameters by analysis of the gate voltage dependence of MOSFET conductivity.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 66–72, November, 1979.     

Deep impurity levels in indium antimonide

The wave functions of the ground and excited states and the energy spectrum of the deep acceptor center in indium antimonide are calculated allowing for the polarization corrections to the potential in a two-band approximation. The polarization correction was calculated using a cavity model.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 38–42, October, 1972.In conclusion we should like to thank Z. I. Uritskii for his guidance in this study.     

Magneto-Raman scattering inp-type indium antimonide

We report for the first time stimulated magneto-Raman scattering inp-type InSb. Two different Raman scattering processes were observed. The first one has a Raman shift of about 2cm⁻¹/kG and is observed at magnetic fields up to 30kG. The other one is observable only at high magnetic fields above 30kG and shows Raman shifts between 1.2cm⁻¹ and 3.0cm⁻¹ with a tuning rate of about 0.2cm⁻¹/kG. The first process can be interpreted either as spin-flip Raman scattering by photo-excited electrons in the conduction band or as Raman scattering by holes in the valence band involving transitions from heavy to light hole states. The other Raman shift observed seems to occur on account of transitions between the heavy hole ladders.     

Diffusion coefficient of selenium in indium antimonide

The diffusion of selenium in indium antimonide has been studied in the temperature range 400–490°C, by the method of removing layers. Two regions have been distinguished in the donor distribution profiles. The first has a low diffusion coefficient and a high surface concentration, near to the limit of solubility of selenium (8·10¹⁸ cm^–3). In the second region, a much larger diffusion coefficient and a surface concentration lower by two orders of magnitude (8·10¹⁶ cm^–3) with weak temperature dependence are found. The temperature dependences of the diffusion coefficients of the first and second regions can be described by the expressions: D=4.8·10¹³ exp(–4.1 eV/kT) cm²/sec, D₂=1.9·10¹³ exp(–3.9 eV/kT) cm²/sec.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 40–43, November, 1991.     

Negative photoconductance in thin indium antimonide films

Negative photoconductance or optical quenching has been observed in thin InSb films, fabricated by vacuum evaporation on glass substrates. An electronic flash was used as the light source. The time constant of the photocurrent measured on several samples ranges from 30 sec to 3 min. Whereas bulktraps localised in the narrow band gap of InSb (0.18 eV) can hardly be responsible for the high time constants, it is believed that slow surface traps or traps inside an In₂O₃ layer, covering the InSb film, are responsible for the optical quenching.     

Magnetically stabilized electron-hole liquid in indium antimonide

Luminescence spectra of sufficiently pure n-type indium antimonide crystals (N _D−N _A=(1–22)·10¹⁴ cm⁻³) in a magnetic field of up to 56 kOe, at temperatures of 1.8–2 K, and high optical pumping densities (more than 100 W/cm²) have been studied. More evidence of the existence of electron-hole liquid stabilized by magnetic field has been obtained, and its basic thermodynamic parameters as functions of magnetic field have been measured. When the magnetic field increases from 23 to 55.2 kOe, the liquid density increases from 3.2·10¹⁵ to 6.7·10¹⁵ cm⁻³, the binding energy per electron-hole pair rises from 3.0 to 5.2 meV, and the binding energy with respect to the ground exciton level (work function of an exciton in the liquid) rises from 0.43 to 1.2 meV. Zh. éksp. Teor. Fiz. 111, 737–758 (February 1997)     

Intensity dependent Faraday rotation in indium antimonide

Intensity dependent interband Faraday rotation has been observed in InSb using a low power cw CO laser. The dependence of induced rotation on incident power and frequency shows saturation and resonance enhancement effects. The induced rotation is qualitatively attributed to the dispersion associated with saturable absorption of a valence to conduction band magneto-optical transition and includes an acceptor impurity effect. Induced rotations of >10³ degrees/W cm were observed.     

Anisotropic growth of indium antimonide nanostructures

InSb nanostructures have been synthesized by the use of gas aggregation process. Nanoparticles with different shapes are obtained by controlling the growth and deposition temperature of the InSb nanoclusters. Triangular nanocrystals are commonly observed when the clusters are extracted from the condensation chamber of the source and deposited on the room temperature substrate at high vacuum. When the deposition is performed inside the condensation chamber at high temperature near the melting point of bulk InSb, nanoparticles formed on the substrate surface show several kinds of 3-dimensional morphologies, such as triangular or rectangular prisms, as well as hexagonal tablets. Keeping the same conditions for the cluster source operation and deposition, after long time growth, nanorods with hexagonal and quadrangular cross sections are formed through vapor-liquid-solid (VLS) process. The origin of the difference on the morphologies and shapes of the nanostructures is attributed to the anisotropic growth of InSb, which is temperature dependent.     

The photo-electric properties of indium antimonide

A change of resistance or the formation of a voltage in mono- or polycrystalline samples of InSb due to illumination has been observed, the magnitudes of which increase with decreasing temperatures. It is demonstrated that this is a photo-conductive effect, arising in the volume of the sample or at barriers due to non-homogeneities, and a photo-voltaic effect. The spectral curves were measured with long-wave limits _1/2=5.8 at –155 °C, _1/2=6.7 at –42 °C.It is shown that these phenomena are caused by the transition of electrons from the valence-bond band to the conduction band under the influence of photons. The width of the band of forbidden energy values below room temperature was found to be E _G=0.24–2.4×10^–4T(eV).It is our pleasant obligation to thank Prof. Dr. L. Zachoval for permission to perform certain parts of this work in the Physics Institute of Charles' University, and Ing. A. Vaek and Dr. J. Plíva for valuable advice in carrying out the measurements and Ing. K. mirous for preparation of the samples.     

Electron scattering with spin flip in indium antimonide and indium arsenide

The longitudinal magnetoresistance has been investigated at temperatures in the range from 2.8 to 200 K in a magnetic field of up to 200 kOe with the aim of determining the temperature range and the magnetic field strength at which charge carrier scattering with spin flip occurs in n-type indium arsenide and n-type indium antimonide. It is established that quantum oscillations of the longitudinal magnetoresistance of indium arsenide exhibit weak zero maxima due to electron scattering with spin flip at temperatures in the range from 4 to 35 K in a magnetic field of 146 kOe. For the longitudinal magnetoresistance of indium antimonide, zero maxima caused by electron scattering with spin flip are revealed in the temperature range from 60 to 80 K in a magnetic field of 132 kOe.     

HF sputtered indium oxide films doped with tin

Indium-tin-oxide films (ITO films) sputtered in Ar-atmosphere with and without addition of oxygen reveal an irreversible increase in conductivity during annealing in vacuum. This annealing process increases drastically the density of free electrons, while the Hall mobility changes only slightly. Below the annealing temperature the temperature dependence of the conductivity is reversible. In films with low density of free electrons, which behave like non-degenerated semiconductors, two activation energies for the mobility could be found. The irreversible changes, observed during annealing in the vacuum, are explained by diffusion of oxygen from the interior of the film to the surface, followed by desorption of the oxygen from the surface into the vacuum. The excess oxygen in the non-stoichiometric films plays the role of electron traps. The irreversible effects during annealing in the vacuum are partly reversible in the long run. If the annealed films are exposed to oxygen or air their conductivity decreases because of diffusion of oxygen from the surface into the film.     

Density of indium antimonide at high temperatures

The density of solid and liquid indium antimonide was studied by irradiating the samples with a narrow beam of monochromatic gamma-radiation in the temperature range of 293–1950 K, including the range of melting — crystallization. The measurement errors for the density and thermal expansion coefficients were ±(0.25–0.40) % and ± 4 %, correspondingly. The approximating equations and tables of reference data were obtained for the temperature dependence of thermal properties. Measurement results were compared with the known published data. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 06-08-00040).