Drag current for ionization of impurities by an electromagnetic wave in a semiconductor superlattice

The drag current for ionization of a shallow impurity by a strong electromagnetic wave in a semiconductor superlattice is found. It is shown that at low temperatures, when it is possible to ignore the equilibrium carrier density, the dependence of the drag current on the intensity of the electromagnetic wave is nonlinear and it oscillates with growth of the intensity of the electromagnetic field. These oscillations are a consequence of the many-photon character of absorption of the electromagnetic wave by the impurities and also of nonparabolicity of the energy spectrum of the superlattice. A comparison is made of the contributions to the drag current from the anisotropic part of the impurity ionization probability and from its isotropic part, with allowance for modification of the distribution function by the electromagnetic wave. It is found that for (Δ is the width of the conduction miniband) the main contribution to the drag current comes from the isotropic part of the ionization probability. Fiz. Tekh. Poluprovodn. 33, 1443–1446 (December 1999)     

Photoconductivity of the germanium-doped solid solution p-GaAs0.94Sb0.06

A new mechanism of impurity photoconductivity in semiconductors has been discovered. The form of the long-wavelength photoconductivity spectra observed in p-GaAs_0.94Sb_0.06: Ge is satisfactorily explained in terms of resonance ionization of impurity levels by phonons excited during absorption of infrared radiation. Fiz. Tekh. Poluprovodn. 31, 475–477 (April 1997)     

Frenkel’-Poole effect for boron impurity in silicon in strong warming electric fields

A method based on measurement of the thermally stimulated conductivity of a weakly compensated semiconductor, which is doped with a deep impurity and which contains an impurity component that is shallower than the main component, has been developed for investigating the Frenkel’-Poole effect. The results of an investigation of the thermally stimulated conductivity of Si:Ga samples with gallium density N _A =(2–3)×10¹⁸ cm⁻³ and low accompanying impurity content (⩽10¹³ cm⁻³) are reported. The conductivity was measured after extrinsic photoexcitation of samples heated at a rate β=0.6 K/s in the temperature range T=4.2–24 K in electric fields E=20–1000 V/cm. It is shown that the maximum on the curves of the thermally stimulated conductivity is due to the thermally stimulated emptying of the boron impurity and shifts to lower values of T as E increases. The decrease of the ionization energy of impurity B in an electric field, which turns out to be somewhat weaker than the field according to the Frenkel’-Poole model for singly charged Coulomb centers, is found from the shift of the maximum. Fiz. Tekh. Poluprovodn. 31, 777–780 (July 1997)     

Current-voltage characteristics of Si:As blocked impurity band photodetectors with hopping conductivity (BIB-II)

The current-voltage characteristics of Si:As blocked impurity band (BIB) structures are investigated. The behavior of the dark current in the temperature range 4.2–25 K and in the range of bias voltages −3 to +3 V is analyzed. It is shown that the main features of the I-V characteristics are governed by the thermal-field injection of charge carriers from the contacts to the BIB structure. The details of the I-V characteristics for bias voltages of both polarities are attributed to generation-recombination processes between the conduction band and the impurity band of the N ⁺ photoconductive layer. It is established that the blocking layer can accumulate charge of both signs, influencing the formation of the dark I-V characteristics. Fiz. Tekh. Poluprovodn. 33, 1005–1009 (August 1999)     

Influence of the intensity of gg irradiation on the photoluminescence of GaAs:Te

The influence of gg irradiation (⁶⁰Co) of various intensities (P _γ≈1.7−7.5kGR/h) on the photoluminescence of GaAs:Te single crystals [n ₀=(1.2–2.3×10¹⁸ cm⁻³] is investigated. Together with the known photoluminescence impurity bands (hν _max≈1.2 eV and/or hν _max≈1.35 eV) and edge band (hν _max≈1.51 eV), new bands are also observed in the spectra at hν _max≈1.3 eV and hν _max≈1.48 eV. The observed effects are attributed to radiation-stimulated ordering of the donor impurity and deep impurity centers. Fiz. Tekh. Poluprovodn. 32, 38–39 (January 1998)     

Nature of the donor action of Gd impurity in crystals of lead and tin telluride

Electron spin resonance and the Hall effect are investigated in n-Pb_1−x Sn_xTe:Gd crystals grown from melt. It is found that there is no direct correlation between the free electron density and the density of the Gd³⁺ impurity in these crystals. The conclusion is drawn that the the electron conductivity of Pb_1−x Sn_xTe:Gd crystals is not caused by the Gd impurity but by intrinsic defects of the crystal lattice which have zero activation energy due to the Gd impurities. Fiz. Tekh. Poluprovodn. 32, 1331–1333 (November 1998)     

Formation of Se2 quasimolecules in selenium-doped silicon

The kinetics of the formation of impurity complexes associated with selenium is investigated. The stationary density of complexes is obtained as a function of temperature and the density of selenium atoms that occupy silicon lattice sites. It is established that in the process of interconversions of electrically active complexes in the temperature range 670–1000 °C the total number of atoms participating in complex-forming reactions remains unchanged at any point of the spatial distribution of the impurity. The kinetics of accumulation of centers with ionization energy 0.2 eV is satisfactorily described by a scheme of quasichemical reactions leading to the formation and decomposition of Se₂ quasimolecules. In the ideal, strongly dilute solution approximation the binding energy of a Se₂ quasimolecule is 1.35 eV. Fiz. Tekh. Poluprovodn. 32, 1306–1312 (November 1998)     

Effect of deep levels on current excitation in 6H-SiC diodes

The results of an experimental study of deep levels in the p-base of 6H-SiC diodes are presented. A deep level of unknown origin, with ionization energy E _c -1.45 eV, acts as an effective recombination center for minority carriers, and controls recombination processes. A level with ionization energy E _c -0.16 eV is attributed to a nitrogen donor impurity. Electron capture and thermal activation processes associated with this level substantially extend the duration of current relaxation in the p-n junction. Fiz. Tekh. Poluprovodn. 31, 1220–1224 (October 1997)     

Effect of impurities with variable valency on the transport phenomena in a quantum well

Transport phenomena in a quantum well containing a multivalent impurity are investigated on the basis of a model of strong Coulomb correlations. It is shown that as the iron content in the quantum well increases, the Coulomb correlations grow and produce ordering in the impurity system. As a result, the scattering of 2d electrons by them should weaken, and this should result in a substantial increase in the mobility of 2d electrons. Fiz. Tekh. Poluprovodn. 31, 769–773 (April 1997)     

Current-voltage characteristics of GaN and AlGaN p-i-n diodes

The current-voltage characteristics of GaN and Al_0.08Ga_0.92N p-i-n diodes were investigated. The experimental p-i-n structures were grown by MOCVD on 6H-SiC with Si and Mg as dopants. The i region was formed by simultaneously doping with donor and acceptor impurities during growth. Analysis of the current-voltage characteristics showed that current flow in the p-i-n diodes is due to either drift of thermally excited holes or electron-hole recombination in the i region via impurity centers—just as predicted by the Ashley-Milnes theory. These impurity centers are attributed to Mg acceptor levels. Fiz. Tekh. Poluprovodn. 32, 369–372 (March 1998)     

Structure of DX-like centers in narrow-band IV–VI semiconductors doped with group-III elements

This paper presents a study of the structure of the IR reflectance spectra in the sub-gap region of lead telluride doped with indium and gallium and the Raman spectra in PbTe(In). In the Raman and reflectance spectra of PbTe(In), features are observed at a frequency of ω ₀⋍120 cm⁻¹, whose amplitude sharply increases at temperatures T below the temperature where delayed photoconductivity appears, T _c⋍25 K. A similar feature at a frequency of ω ₀⋍155 cm⁻¹ is also observed in PbTe(Ga), with the amplitude of the feature sharply increasing for T>T _c⋍80 K. An analysis of the resulting data makes it possible to conclude that, in contrast with classical DX centers in III–V semiconductors, the microscopic structure of the impurity centers in the two-electron (DX-like) ground state does not correspond to an impurity atom shifted from a lattice site, whereas the impurity atom is shifted from a lattice site for the metastable one-electron impurity state. Fiz. Tekh. Poluprovodn. 32, 679–683 (June 1998)     

Photovoltaic effect in the impurity absorption region of Si-structures with blocked impurity conductivity

A study is made of the field dependence of the photoconductivity in two-layer Si:Sb-and Si:Bstructures with blocked impurity-band conductivity and different thicknesses of the undoped (blocking) layer. The impurity concentration in the doped (active) layer was ≈10¹⁸ cm⁻³. Measurements were made at temperatures T=4–15 K for high (Φ∼10¹⁶ photons/cm² · s) and low (Φ<10¹⁴ photons/cm² · s) incident photon fluxes. A photovoltaic effect is observed in the Si:B structures with a thin (3 μm) blocking layer. It is found that a photovoltage develops for photons with energies exceeding the ionization energy of boron and its magnitude is independent of the photoexcitation intensity (for Φ>10¹³ photons/cm² · s) and, in the limit of low temperatures, it is close to the activation energy ɛ ₃ for jump conductivity in the active layer. The photovoltaic effect is explained by ballistic transit of the blocking layer by holes emitted from the contact which are then cooled in the active layer, as well as by the presence of a potential barrier ≈ɛ ₃ between the active and blocking layers. These factors are taken into account in a model for describing the major features of the dependence of the photovoltage on temperature and on the photon intensity and energy. Fiz. Tekh. Poluprovodn. 33, 456–463 (April 1999)     

Electromagnetic waves in cylindrical plasma-dielectric structures

The theory of electromagnetic waves in cylindrical structures (waveguides) with plasma and plasma-dielectric fillings is presented in a systematic form. The case of isotropic cold electron plasma with sharp transverse plasma/vacuum, plasma/dielectric, plasma/plasma, and plasma/metal interfaces is considered. Particular attention is given to surface plasma waves and their interaction with bulk electromagnetic modes. The coupling of E and B waveguide modes that is due to the transverse inhomogeneity is investigated. The important question of the applicability of the potential (electrostatic) approximation in the theory of plasma waves and the role of nonpotential effects are discussed. Original Russian Text ? A.F. Aleksandrov, M.V. Kuzelev, A.A. Rukhadze, 2008, published in Radiotekhnika i Elektronika, 2008, Vol. 53, No. 12, pp. 1445–1465.     

Amplification of electromagnetic waves at odd harmonics of the cyclotron resonance of heavy holes with negative effective masses in semiconducting diamond

It is shown theoretically that the absorption coefficient for circularly polarized electromagnetic waves at the cyclotron resonance of heavy holes with negative effective masses in diamond in parallel electric and magnetic fields oriented along the [001] crystal axis takes negative values at the frequency of any of the n+1 harmonics (n=0,4,8, etc.) for the right (electron) polarization and at the frequency of any of the n−1 harmonics (n=4,8,12, etc.) for the left (hole) polarization. In an electric field E≈10⁴ V/cm and magnetic fields H=30–80 kOe, at lattice temperatures of 77–100 K, and for a hole concentration of (3–5)×10¹⁵ cm⁻³, the absorption coefficient for an electromagnetic wave at the third harmonic ω ₃=3ω=2.5×10¹² s⁻¹ (wavelength λ₃=0.92 mm) is as high as η ₃=(−7)–(−30) cm⁻¹. Fiz. Tekh. Poluprovodn. 32, 504–508 (April 1998)     

Fabrication of blocked impurity-band structures on gallium-doped silicon by plasma hydrogenation

The electrical characteristics of blocked impurity-band structures (BIB-structures) based on gallium-doped silicon (N _Ga≈5×10¹⁷ cm⁻³) are investigated. The blocking layers were formed by passivation of the gallium impurity by means of treatments in an rf-discharge hydrogen plasma at substrate temperatures T=20–220 °C. It is found that the activation energy E _a of the hopping conductivity with hopping between nearest gallium neighbors decreases from 8.7 meV (before hydrogenation) to 1.3 meV (after hydrogenation at T=220 °C). The current-voltage characteristics and temperature dependence of the dark current of the structures and their change after isochronal (t=20 min) annealing at temperatures T=220–400 °C are determined. The current-voltage characteristics of the structures at low temperatures are calculated. The results of calculations are found to agree with experimental data. Fiz. Tekh. Poluprovodn. 31, 311–317 (March 1997)     

Relaxation of the electric field in high-resistivity, strongly biased MISIM structures with deep impurity levels

The relaxation of the field and current in a high-resistivity metal-insulator-semiconductor (MISIM) structure containing a considerable concentration of deep impurity levels after the removal of strongly absorbed light is investigated numerically. It is established that the time dependence of the field distribution is determined by the relation between the times for the thermal generation of electrons (τ _n ) and holes (τ _p ) by an impurity. In the case of the temporal variation of the field in the bulk of the semiconductor is nonmonotonic. The drift of the photogenerated carriers after removal of light leads to the formation of a negative space charge layer of increased density and a significant increase in the field near the anode. Its maximum value can be as high as 5–6 times the mean field E _e =V/d. Consideration of the additional injection of holes from the anode leads to an increase in the current, restriction of the maximum field at the anode, and appreciable acceleration of the relaxation of the field to the dark distribution. Fiz. Tekh. Poluprovodn. 32, 203–208 (February 1998)     

Electron localization in sound absorption oscillations in the quantum Hall effect regime

The absorption coefficient for surface acoustic waves in a piezoelectric insulator in contact with a GaAs/Al_0.25Ga_0.75As heterostructure (with two-dimensional electron mobility μ=1.3×10⁵ cm²/(V·s) at T=4.2 K) via a small gap has been investigated experimentally as a function of the frequency of the wave, the width of the vacuum gap, the magnetic field, and the temperature. The magnetic field and frequency dependences of the high-frequency conductivity (in the region 30–210 MHz) are calculated and analyzed. The experimental results can be explained if it assumed that there exists a fluctuation potential in which current carrier localization occurs. The absorption of the surface acoustic waves in an interaction with two-dimensional electrons localized in the energy “tails” of Landau levels is discussed. Fiz. Tekh. Poluprovodn. 31, 451–458 (April 1997)     

Distribution of the electric field in high-resistivity MSM structures illuminated by nonmonochromatic light

The sensitivity of the electric field distribution to the spectrum of the incident radiation in highly biased, high-resistivity, semiconductor structures of the MSM (metal-semiconductor-metal) type illuminated by nonmonochromatic light is investigated theoretically. It is shown that in the presence of deep impurity levels the field distribution depends strongly on the spectral composition of the incident light. The frequency interval corresponding to optical thicknesses of the order of unity is found to significantly influence the space charge in the bulk of the structure and the electric field distribution E(x), even when the fraction of energy in this region of the spectrum relative to the total flux is extremely minimal. The trapping of holes by a deep impurity level in the bulk of the structure forms a positive space charge and produces qualitatively new field distributions, which increase near the dark electrode with a positive curvature of the function E(x). The impurity trapping of electrons near the illuminated anode imparts a negative space charge to the impurity levels. This phenomenon induces a substantial increase of the field in the electrode sheath and forms in the vicinity of the anode a region wherein the field varies only slightly. All the prominent features disclosed by the calculations in the electric field distributions are observed in experiment. Fiz. Tekh. Poluprovodn. 33, 815–823 (July 1999)     

Low-temperature (77–300 K) current-voltage characteristics of 4H-SiC p+-p-n+ diodes: Effect of impurity breakdown in the p-type base

The effect of impurity breakdown on the low-temperature (77–300 K) current-voltage (I–V) characteristics of 4H-SiC diodes with a p-type base has been studied. Experimental samples were fabricated from CVD-grown (chemical vapor deposition) commercial p ⁺-p-n ⁺ 4H-SiC structures. A high electric field in the p-type base was created by applying a forward bias to the diodes. It was found that, at temperatures of 136, 89, and 81 K, the commonly observed “diode” portion of the I–V characteristics is followed by a portion in which the current grows more rapidly due to the impact ionization of frozen-out Al acceptor atoms in the ground (unexcited) state. At temperatures of 81 and 77 K, this portion is followed by one with a negative differential resistance due to the regenerative dynistor-like switching of the diode, caused by impact ionization of aluminum atoms in the excited state.