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The low-temperature magnetoresistive effect in the semiconductor HgSe:Fe in weak magnetic fields at microwave frequencies is examined. The negative and positive components of magnetoabsorption based on the magnetoresistive effect in the degenerate conduction band are analyzed. The special features of experiments carried out in the investigated frequency range are noted. The momentum and electron-energy relaxation times are determined from the experimental field and temperature dependences.

The method of superconducting quantum interference device (SQUID) magnetometry is used to measure and study low-temperature (T ≤ 100K) susceptibility in a series of samples of heavily doped Ge:As samples on the insulator side of the insulator–metal phase transition. Subtracting the known values of the magnetic susceptibility of the lattice from the measurement results, the values of the impurity magnetic susceptibility of the system are obtained. Using the method of electron spin resonance, the paramagnetic component of the impurity susceptibility is determined. Subtraction of the paramagnetic component from the total impurity susceptibility is used to obtain, for the first time, the values of the impurity diamagnetic susceptibility (~5 × 10–8 cm3/g). The obtained result is consistent with estimates obtained for the localization radius of an electron at an As donor. Lowering the temperature to T ≤ 4 K leads to an increase in the diamagnetic susceptibility, which is consistent with the observed increase in the paramagnetic susceptibility. The observed effect is accounted for by the transition of impurity electrons from the singlet state to the triplet one.

We consider a method for determining the magnetic susceptibility of “poor” conductors using electron paramagnetic resonance data. A method is described on the basis of double integration of the positive part of the derivative of the absorption line that has a Dyson shape. The skin depth is taken into account. Analysis is carried out for germanium samples doped by arsenic in the range of high concentrations corresponding to the insulator-metal transition.

The phenomenon of the low-temperature transition from antiferro- to ferromagnetic ordering of impurity spins in a nonmagnetic compensated n-Ge:As semiconductor near the metal-insulator phase transformation has been experimentally observed. The effect is manifested by rather sharp changes in the spin density and g-factor in the electron spin resonance spectra. As the relative content of a compensating impurity (gallium) is reduced below 0.7, the transition temperature begins to decrease and, at a degree of compensation below 0.3, drops below the studied temperature range (i.e., below 2 K).

To determine the electronic properties of metal-carbon clusters, palladium clusters are introduced into nanoporous carbon samples. The structural and magnetic properties of the nanocomposite thus obtained are investigated. A ferromagnetic resonance (FMR) component is observed in the electron spin resonance (ESR) spectra measured in a wide temperature range. The electron density of states (DOS) of clusters consisting of a palladium atom surrounded by carbon atoms is calculated, and it is shown that, due to the interaction between electronic terms of carbon and metal, such a cluster should exhibit magnetism. The investigation of the structures of the porous skeleton of nanoporous carbon and of palladium clusters has allowed us to reveal how carbon and palladium atoms are brought into close contact so that to give rise to the observed ferromagnetism.

A low-temperature (3–100 K) electron spin resonance (ESR) study of the spin system of neutral As donors in Ge showed that on the insulator side of the insulator-metal transition the single-spin density exponentially disappears as T → 0. Such spins are bound into pairs to give an antiferromagnetic (AF) phase. Upon increasing the temperature the AF phase is destroyed, the single-spin density and, as a result, the ESR absorption signal becomes stronger. The temperature dependences of the densities of the pairs and single spins are typical for a chaotic distribution of neutral donors. In this case, there is no Neel temperature. For a low degree of compensation, the crystal lattice of Ge with the AF phase is actually a nanostructured system characterized by anisotropic internal stresses that are the strongest along one of the [110] directions. These stresses give rise to the anisotropy of the g-factor which is responsible for experimentally observed splitting of the ESR line. The compensating impurities destroy the AF phase and reduce this splitting. Local stresses are present in this case, too, but now they appear because of the Coulomb interaction of oppositely charged impurities and have no preferred orientation.

The effect of spin interaction on the width and shape of the electron spin resonance line in compensated and uncompensated n-Ge:As has been studied. It is shown that, in the case of a magnetic field oriented along the [100] axis, the width of the resonance line decreases irrespective of the degree of compensation as the critical concentration of the insulator-metal transition is approached, owing to enhancement of the exchange interaction of spins and to an increase in the spin relaxation time. When the magnetic field is directed along other axes, an additional line broadening appears in compensated samples. This broadening is determined by the influence exerted on the g factor by fluctuations of the internal electrostatic field via the stresses generated by these fluctuations. For well-conducting samples, in which the thickness of the skin layer becomes smaller than that of the sample, the line takes on an asymmetric (Dysonian) shape. In this case, the ratio between the wings of the derivative, characteristic of this line shape, is determined by the ratio between the rates of spin diffusion and spin relaxation.

It is shown that, on the insulator side of the insulator – metal transition, the single spin density exponentially disappears as T 0. Such spins are bound into pairs to give an antiferromagnetic (AFM) phase. Upon an increase in temperature the AFM phase is destroyed, the single-spin density, and, as a result, ESR absorption signal becomes stronger. The temperature dependencies of the densities of the pairs and single spins are typical of a chaotic distribution of neutral donors. In this case, there is no Neel temperature. In low degree of compensation, the crystal lattice of Ge with the AFM phase is actually a nanostructured system characterized by anisotropic internal stresses that are the strongest along one of the [110] directions. These stresses give rise to anisotropy of the g-factor which is responsible for experimentally observed splitting of the ESR line. The compensating impurities destroy the AFM phase and reduce this splitting. Local stresses are present in this case, too, but now they appear because of the Coulomb interaction of oppositely charged impurities and have no preferred orientation. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We show for n -type semiconductors, using Ge:As and 4H -SiC:N as examples, that the spin density measured by electron spin resonance (ESR) falls sharply near the insulator–metal (IM) transition. Two reasons might be responsible for this phenomenon: potential fluctuations with concentration of the electrons in local minima or local antiferromagnetic spin pairing (“spin glass”) in the insulating state just below the IM transition. In the investigated semiconductors manifestation of the latter is observed as a change from Curie to a Curie–Weiss behaviour with negative constant Θ. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Cobalt clusters were embedded into a nanoporous carbon powder (with pores about 2 nm in size) prepared from a B4C carbide powder. Electron spin resonance (ESR) measurements were carried out within a broad temperature range. At all temperatures, the ESR spectrum consisted of two overlapping resonance Lorentzian lines. The temperature dependences of the integrated intensities and linewidths and of the resonance fields were determined. A theoretical analysis of these dependences shows that they can be described in terms of the theory of a disordered magnetic medium with two spin systems with different properties.

Photonic band gap (PBG) based elements can significantly contribute to future integrated optical circuits. However, at the wavelength of 1500 nm, they require about 100 nm feature size lithographic processes, which, until now, have been typically accomplished with the help of e-beam lithography. Taking into account that all non-periodic features, e.g. waveguides and cavities, require only ∼300 nm resolution, the process can be separated in two stages. First, interference lithography is used for creation of periodic patterns with minute feature sizes. Second, the non-periodic lower resolution features are added by standard ultraviolet lithography. Using this method 1.3 μm thickness waveguides in 100 nm feature size hexagonal PBG environment were fabricated from high refractive index ( n = 2.2–2.5) chalcogenide photoresists.

The first observation of low-temperature magnetoresistance (MR) of interference nature in the case of a light doping is reported. The MR occurs in n- and p-type Ge samples at a frequency of 10 GHz at temperatures below 30 K in weak magnetic fields on the background of the classical MR effect associated with electrons in different valleys (n-Ge) and with heavy and light holes (p-Ge).

The variation in the width and shape of the ESR line of nitrogen in 4H-SiC in the concentration range corresponding to the insulator-metal phase transition was investigated. It is shown that the spin relaxation in the region of hopping and metal conduction occurs at electrical multipoles (clusters) whose sizes decrease from rather large to small (characteristic of interimpurity distances) as the concentration of impurity centers increases. Analysis of the temperature dependences of the resistance made it possible to estimate the critical concentration for the insulator-metal phase transition (ND-NA)c≈1.5×1019 cm−3. The values of other characteristic concentrations that determine the effects of electron-electron interaction in the system under study were also found.

The electron spin resonance investigation in the insulator phase of compensated n-Ge:As shows that near the insulator–metal transition the weakly localized electrons are connected in the pairs with the antiparallel coupled spins. As a result, the antiferromagnetic spin glass structure is produced. The main manifestations of the phenomenon are the fall of the (free) spin density and a g-factor shift to the strong magnetic field with the electron concentration growth in the pretransition range. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Special features of electron spin resonance in the vicinity of the insulator-metal phase transition in n-type 4H-SiC:N were investigated. It was shown that, in the insulating state, an antiferromagnetic phase of the spin-glass type is formed in this region. As a result, with increasing doping level, the content of the paramagnetic phase decreases, and, at an impurity concentration close to critical (corresponding to the transition), the resonance line of nitrogen atoms disappears. Instead of it, a line of deep-level impurity centers is observed at the same position in the metallic state. In addition, two new lines are observed in the metallic state in strong fields; these lines are attributed to free charge carriers.

Measurements of the electrophysical properties of nanoporous carbon (NPC) samples (conductivity and Hall effect), as well as studies of the same samples using electron spin resonance (ESR), are summarized. Free holes are shown to play the major part in charge transport in such materials, thus permitting identification of the ESR signal with free holes. An analysis of the shape of the resonance lines, as well as of their dependence on temperature and the technology employed in sample preparation, established the ESR signals to consist of two superimposed resonance lines associated with carriers, free or localized to various extents, whose magnetic susceptibility obeys Pauli and Curie-Weiss laws, respectively. The temperature dependences of the ESR signal parameters were studied, and the experimental relations were compared with theory to determine the model-parameters. An analysis of the temperature behavior of these parameters suggests the conclusion that NPC samples are heterophase porous systems whose properties are dominated by structural characteristics.

A new form of carbon material, a low-density cluster-assembled carbon nanofoam was produced by high-repetition-rate laser ablation of a glassy carbon target in an ambient non-reactive Ar atmosphere. The foam poses a unique combination of properties, such as one of the lowest solid density and high resistivity, similar to that of amorphous diamond-like films. Electron energy loss spectra demonstrate that the carbon foam has a significant, 35% in average, fraction of sp 3 -bonding. The measured density of spins in the foam, 8.8×10 20 g −1 , is one of the highest observed in tetrahedrally-bonded carbon. This density of spins corresponds to paramagnetic susceptibility of about 0.01 of that for transition metals, which is in a striking contrast to diamagnetic properties of all other known allotropes of carbon.

The microwave magnetoresistance (MR) of neutron transmutation doped (moderately compensated) Ge:Ga in the insulator-metal transition region was studied using ESR technique. As the hole concentration increases, the MR mechanism changes in the insulator state near the phase transition point: the hopping conductivity that is characterized by the impurity wave-function contraction by the magnetic field is replaced by the state of weak localization. In the latter case, the temperature dependence of the diffusion coefficient is of great importance near the transition point (1.2×1017 cm−3). This dependence decreases in the metallic state. In the metallic state, the diffusion coefficient is independent of temperature and the MR temperature dependence is described by the dephasing mechanism due to phonon scattering. The electron-electron interaction contribution to the dephasing time should be considered for heavier doping.

The contactless technique of electron spin resonance was used to measure magnetoresistance (MR) phenomena in heavily doped and compensated Ge : Ga both in the insulator and metallic phases near the insulator-metal (IM) transition. The concentration dependency of the temperature power coefficient of the MR allows us to identify the effect origin versus the hole density. They are: the wave function shrinkage by magnetic field at p 1.5 × 10 17 cm -3 .

Electron spin resonance (ESR) was investigated in the vicinity of insulator-metal (IM) transition in 4H-SiC : N. The ESR spectra transformation was observed from an electron concentration of n = 2.5 x 10 17 to 2.5 x 10 19 cm -3 ; The increase of the spin density with the electron one was measured for n 6 x 10 18 cm -3 . The critical electron density was estimated for the insulator-metal (IM) transition in 4H-SiC n c = 1 × 10 19 cm -3 . In the vicinity of the IM transition three new ESR lines were found: the first was originated from the deep defects, the second and the third were due to the free spins in the impurity or in the conduction band.

The magnetoresistance of heavily doped Ge:As near the metal-insulator phase transition has been studied both on the metal and insulator sides of the transition. Measurements were made at microwave frequencies using a noncontact technique of electron spin resonance. The field and temperature dependences of the magnetoresistance derivative in metallic samples reveal two main features of the phenomenon: a negative magnetoresistance at weak fields, due to the weak localization effect, and a positive magnetoresistance at strong fields, arising from the electron-electron interaction in the diffusion channel. Only a weak negative magnetoresistance with a characteristic low-field behavior is observed in insulating samples. The results are compared with the theory of quantum corrections.

Electron spin resonance (ESR) is investigated in the vicinity of metal-insulator transition in compensated n-Ge:As. It is found that the 10-GHz signal is observed from both sides of the transition up to a temperature of 100 K. ESR spectrum in metallic samples looks like a single line of the Dyson type, with the line shape varying with temperature. The Dyson line in the insulating samples transforms into the Lorentz line which splits into two lines at temperatures below 4.1 K. One line has an ordinary shape, the other has an anomalous step-like shape in the magnetic field, increasing with decreasing temperature. This effect has not been satisfactorily explained so far. Two mechanisms are proposed for the spin relaxation observed, one of which is related to donor-acceptor pairs and the other, to phonons. The Pauli and Curie paramagnetism is found in metallic and insulator samples, respectively.

The role of small heat-shock proteins in Escherichia coli is still enigmatic. We show here that the small heat-shock protein IbpB is a molecular chaperone that assists the refolding of denatured proteins in the presence of other chaperones. IbpB oligomers bind and stabilize heat-denatured malate dehydrogenase (MDH) and urea-denatured lactate dehydrogenase and thus prevent the irreversible aggregation of these proteins during stress. While IbpB-stabilized proteins alone do not refold spontaneously, they are specifically delivered to the DnaK/DnaJ/GrpE (KJE) chaperone system where they refold in a strict ATPase-dependent manner. Although GroEL/GroES (LS) chaperonins do not interact directly with IbpB-released proteins, LS accelerate the rate of KJE-mediated refolding of IbpB-released MDH, and to a lesser extent lactate dehydrogenase, by rapidly processing KJE-released early intermediates. Kinetic and gel-filtration analysis showed that denatured MDH preferentially transfers from IbpB to KJE, then from KJE to LS, and then forms a active enzyme. IbpB thus stabilizes aggregation-prone folding intermediates during stress and, as an integral part of a cooperative multichaperone network, is involved in the active refolding of stress-denatured proteins.

Magnetic-field-dependent microwave absorption and electron spin resonance are used to investigate magnetoresistive effects in strongly doped n-InAs. It is shown that these effects can be traced back to negative, positive, or oscillatory magnetoresistance (i.e., the Shubnikov-de Haas effect). While the experimental data are in agreement with the predictions of theory in the latter two cases, for the negative magnetoresistance there are features that are difficult to interpret, especially the absence of any effect at very small fields, much smaller than the characteristic field Hϕ that appears in the theory of quantum corrections, and the two-dimensionality of bulk samples in fields much larger than Hϕ implied by the observed dependences on temperature and to some extent on the magnetic field.

Quantum magnetoresistance effects (negative magnetoresistance and Shubnikov-de Haas effect) have been studied for the first time at the microwave frequencies in a heavily doped semiconductor using the electron paramagnetic resonance technique which improves the accuracy and sensitivity of measurements as compared with the dc mode. Whereas the Shubnikov-de Haas effect exhibits conventional behavior, the negative magnetoresistance was found to show two peculiarities: disappearance of the effect in very weak fields H ≤ 1 Oe at low temperature and anomalous two-dimensional conducting skin-layer.

Nd-doped glassy As2Se3 and As2S3 films are prepared using vacuum co-evaporation of crushed glassy chalcogenide material and Nd2S3 powder. The films display strong Nd photoluminescence with maxima at ∼1080 nm and ∼900 nm and photostructural transformations (photodarkening and photoresist effect). Fabrication of luminescent diffraction gratings using Nd-doped films is also demonstrated.

Thin films fabricated by coevaporation in vacuum of chalcogenide glass and a rare-earth (RE) containing material are shown to have strong rare-earth photoluminescence, photostructural transformations and photoinduced anisotropy. The photoluminescence spectra of the films are similar to that of very different Nd- and Er-doped solids. Effects of concentration quenching of luminescence and luminescence fatigue are observed and studied. Using the photoresist effect of the doped films, binary diffraction gratings possessing strong IR photoluminescence were prepared.

The low-temperature transformation from antiparallel to parallel spin orientation in a nonmagnetic compensated system Ge:As semiconductor near the metal-insulator phase transition has been experimentally observed. This effect is manifested in the temperature dependences of the impurity magnetic susceptibility obtained by integration of the spin resonance absorption line. These dependences show that the spin density falls in the medium temperature range (10-100 K) and grows at low temperatures. The effect is confirmed by the specific temperature features of the g-factor and inverse magnetic susceptibility. As the relative content of a compensating impurity (gallium) is made lower than 0.7, the transition temperature begins to decrease and, at a degree of compensation < 0.3, falls outside the temperature range under study (i.e., below 2 K).

Behavior of the paramagnetic susceptibility in Si:P at low temperatures was investigated by Electron Spin Resonance in order to detect the antiferromagnetic and ferromagnetic ordering in the vicinity of the insulator-metal phase transition. A procedure was developed to operate sufficiently smooth changes of the spin density, by proton irradiated.

Electron spin resonance (ESR) was investigated in the vicinity of the insulator–metal (IM) phase transition in 4H–SiC:N. The spin density in the vicinity of this transition quickly decreases with the electron concentration growth. This phenomenon is resulted of the antiferromagnetic spin-glass formatting. The spin density temperature dependence confirms this origin.

The microwave absorption in a weak magnetic field H ⪡ H c ( T ) is reported in pure polycrystalline tin in the superconducting state near T c . A novel experimental technique is used which employs an ESR apparatus with the perpendicular configuration of the static and microwave magnetic fields and the radio-frequency modulation of the static field. This measurement is related to the true superconducting state of the bulk material. The characteristic decrease of the microwave absorption in a static magnetic field is detected at 0.8 T / T c ω / T c = 0.12 which is predicted by the microscopic theory of the surface impedance of type-I superconductors.

Method for determining the magnetic susceptibility in the high doped semiconductors is considered. A procedure that is based on double integration of the positive part of the derivative of the absorption line having a Dyson shape and takes into account the depth of the skin layer is described. Analysis is made for the example of arsenic doped germanium samples at a rather high concentration corresponding to the insulator metal phase transition., Pages 13, figures 9, references 10

Strong Shubnikov-de Haas (SdH) oscillations were observed in the derivative of microwave absorption (f=10 GHz) in InAs/GaSb/AlSb composite quantum wells (CQWs) using electron-paramagnetic resonance spectroscopy at low temperatures (2.7 to 20 K) and in the magnetic field up to 14 kOe. CQWs were grown on n-GaSb:Te(100) and n-InAs:Mn(100) substrates with various widths of QWs by MOVPE. A predominant contribution to the bulk n-GaSb substrate in SdH oscillations was manifested. Two frequencies of the SdH oscillations connected with warping of the Fermi surface of GaSb were found from Fourier analysis. An unusual angular indicatrix was observed in dependence on the orientation of the samples grown on n-GaSb in the magnetic field. The obtained results can be explained by bulk inversion asymmetry, which is a feature of substances with a lack of inversion centers. For CQWs grown on n-InAs:Mn substrate, only several SdH oscillations with higher period were observed. We succeeded in extracting a contribution of the two-dimensional carriers of InAs QW∼H⊥, where H⊥=H·cos Θ, from bulk substrate oscillations using a special spline interpolation from the angular dependence of SdH oscillatory amplitudes in the angle range of 0 to 90 deg.

Construction of three-dimensional photonic crystals for optical wavelengths presents many technological and material science challenges. The submicron-feature-size sculpturing must be performed in high-refractive-index materials. We present the fabrication and optical characterization of ∼750 nm feature-size simple cubic woodpile photonic crystals from As2S3 (n≈2.2). The process is based on interference lithography and the layer-by-layer construction.

A study of the electron spin resonance in Ge:As revealed that, in uncompensated semiconductors with shallow impurity levels, the insulator state is preserved near the insulator‐metal phase transition because of the appearance of lattice distortions caused by interaction of spins localized on impurity atoms. We consider this effect as variation of the spin‐Peierls transition. In Ge:As, this effect is manifested at carrier concentrations n = 3×1017–3.7×1017 cm−3. Owing to the random distribution of impurities in the Ge lattice, the properties of this transition differ from those of a similar transition in substances in which uncompensated spins are localized on constituent ions of the host lattice.

Absolute measurements of the magnetic-field-dependent nonresonant microwave absorption have been made in polycrystalline YBa2Cu3O7−δ bulk samples. In low magnetic fields of several Oe the surface resistance at 9.4 GHz has the form of R=R0+βH2 where β = (0.6−2) × 10 −3 Ω/Oe 2 at 4.2 K and (3−8)Ω/Oe2 at 77 K. These values agree rather well with calculations within the model of the effective Josephson medium.

The effects of low-magnetic field microwave absorption (LFMA) and quantum oscillations (QO) discovered earlier in high-temperature superconductors can also be seen in conventional type-I superconductors such as lead, tin, indium and mercury. We have found that both these effects arise from surface irregularity of a sample. LFMA appears when an oxide layer of a few hundred Angstrom; covers the surface and QO are observed in irregular samples with sharp boundaries.

Low-temperature magnetic susceptibility of heavily doped Ge: As samples has been investigated by methods SQUID magnetometry and ESR spectroscopy near the metal-insulator phase transition. Paramagnetic component of the impurity magnetic susceptibility was investigated by ESR previously. Using both techniques make possible to determined the diamagnetic component of impurity susceptibility. The value of the impurity diamagnetic susceptibility equals to 5×10-8 cm3/g and corresponds to the localization radius of the As donor- electron near the metal-insulator phase transition.

We report the production of a hierarchically nanostructured magnetic carbon foam by high-repetition-rate laser ablation of glassy carbon in Ar. The clusters contain both sp2 and sp3 bonded carbon atoms. The material contains graphite-like sheets with hyperbolic curvature, as proposed for "schwarzite". In addition to other unusual properties, the all-carbon nanofoam exhibits para- and maybe ferromagnetic behavior up to 90 K, with a narrow hysteresis curve, susceptibility of the order of 10-5 emu/g Oe, and a high saturation magnetization (up to 0.8 emu/g at 1.8 K). We postulate that localized unpaired spins occur because of topological and bonding defects associated with the sheet curvature, and that these spins are stabilized for >1 year due to the steric protection offered by the convoluted sheets. © 2004 Elsevier B.V. All rights reserved. 290-291 PART 1 298 301 298-301

Electron spin resonance investigation in the insulator phase of compensated n‐Ge:As shows that near the insulator — metal transition the weakly localized electrons are connected in the pairs with the antiparallel coupled spins. As a result, the antiferromagnetic spin glass structure is created. The main manifestations of the phenomenon are the fall of the free (unpaired) spin density, the free spin increase with temperature, and characteristic antiferromagnetic g‐factor shift with the electron density in the pretransition range.

The anomalous magnetoresistance (MR) of the interference origin was first observed in the weakly doped nongenerated n‐Ge:Sb and p‐Ge:Ga. Early proposed for the MR detection, the electron spin resonance technique was used for this investigation. It was found that the anomalous MR was observed in these materials in the temperature range of the classical (nonhopping) motion and in the magnetic fields not higher than some hundred Oersteds. Some peculiarities of the classical MR were observed and explained too.

We report production of nanostructured carbon foam by a high-repetition-rate, high-power laser ablation of glassy carbon in Ar atmosphere. A combination of characterization techniques revealed that the system contains both sp2 and sp3 bonded carbon atoms. The material is a novel form of carbon in which graphite-like sheets fill space at very low density due to strong hyperbolic curvature, as proposed for ?schwarzite?. The foam exhibits ferromagnetic-like behaviour up to 90 K, with a narrow hysteresis curve and a high saturation magnetization. Such magnetic properties are very unusual for a carbon allotrope. Detailed analysis excludes impurities as the origin of the magnetic signal. We postulate that localized unpaired spins occur because of topological and bonding defects associated with the sheet curvature, and that these spins are stabilized due to the steric protection offered by the convoluted sheets., Comment: 14 pages, including 2 tables and 7 figs. Submitted to Phys Rev B 10 September 2003

A GaAs laser diode has been used as the light source for the selective epitaxial growth of GaAs by photoenhanced metalorganic chemical vapor deposition (PE‐MOCVD). The use of GaAs/InGaP layered structures as substrates for these experiments permitted to accurately control the availability of photoexcited carriers reaching the GaAs growth surface. The experimental results obtained rule out pure pyrolysis and photolysis as possible mechanisms responsible for the PE growth rate, and indicate that photoexcited carriers are directly involved in the PE process. The experimental data are consistent with a kinetic model that invokes surface recombination as the main physical mechanism for the PE growth rate effect.

Ridge structures with various widths of about 5 /spl mu/m were selectively grown on open stripe regions between pairs of mask stripes. In narrow regions both lateral gas phase diffusion and substrate migration contribute to the enhanced growth, and affect the surface flatness. In addition, rabbit-ear growth occurs at both edges of selective grown mesa structure and prevents flat burial of the mesa. The results are presented of a study of the effects of sulfur, on the growth rate of InP in selective area growth processes. It was found that the growth rate of the n-type InP layer on the open stripes is a sensitive function of the H/sub 2/S flow rate. It was also found that the growth rate on (100) planes (mesa top) differ frpmm that on (111)B (side facet), and can be controlled by the H/sub 2/S flow rate. A complete growth suppression can be achieved at partial pressure of 2/spl times/10/sup -3/ Torr. Using this novel MOCVD growth technique, a selectively grown buried heterostructure laser diode is successfully fabricated in one step growth.

Magnetosensitive microwave absorption has been studied in oxide glasses enriched with iron or nickel ions. Conditions have been found under which magnetosensitive microwave absorption has the superconducting form, namely, it increases with field in weak magnetic fields, with the derivative of absorption with respect to magnetic field being at a maximum at fields of the order of 100 Oe. For glasses enriched with Fe ions, these conditions are the following: reduction of Fe3+ ions to Fe2+ and presence of Mg ions in the glass. For glasses enriched with Ni ions, the primary condition is formation in these glasses of tetrahedral structural complexes [Ni04]. In our opinion, such an absorption is due to the presence in these glasses of small-sized superconducting inclusions. Ways of increasing the concentration of these inclusions are discussed.

Impurity paramagnetic susceptibility of n-Ge has been measured in the vicinity of the insulator– metal phase transition by two techniques: ESR and SQUID. A comparison of these methods demonstrated that their results qualitatively coincide at low temperatures, but differ at high temperatures. The advantage of the ESR technique is in its substantially higher relative precision, but SQUID makes it possible to obtain on principle absolute values of the magnetic susceptibility. It was found that, in the present-day state of development, the SQUID method has a substantially poorer precision, compared with ESR

A study of the electron spin resonance in Ge:As revealed that, in uncompensated semiconductors with shallow impurity levels, the insulator state is preserved near the insulator-metal phase transition because of the appearance of lattice distortions caused by interaction of spins localized on impurity atoms and the resulting spin-Peierls transition. In Ge:As, this effect is manifested at carrier concentrations n = 3 1017–3.7 1017 cm-3. Owing to the random distribution of impurities in the Ge lattice, the properties of this transition differ from those of a similar transition in substances in which uncompensated spins are localized on constituent ions of the host lattice.

It is shown that the magnetic field dependent microwave absorption in the superconducting tin changes its form when the tin surface is oxidized.