Search

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).

A study of electron spin resonance in uncompensated Ge:As semiconductor samples in the vicinity of the insulator-metal second-order phase transiti on reveals that the interaction of spins localized at As atoms brings about a distortion of the crystal lattice and enhances the localization. This effect occurs in the range of electron concentrations n = 3 × 1017—3.7 × 1017 cm-3, just below the critical point of the phase transition. The effect is explained in the context of a model considering the spin-Peierls transition in the random impurity sublattice of the semiconductor, and its features, as compared to other known materials where the spin-Peierls transition is observed, are understood.

Process of the solid-phase diffusion of manganese into single crystals ZnGeP2 are investigated by electron paramagnetic resonance and X-ray element microanalysis. Conditions for formation of a solid solution with Mn2+ concentration of 1018 cm-3 were found. A diffusion coefficient of manganese in single crystal of ZnGeP2 at a diffusion annealing temperature was determined.

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.

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)

The changes in the spectrum and g factor of electron spin resonance due to the interaction of spins in the insulator state of n-Ge near the insulator-metal phase transition are studied. It is found that, in this region, the g factor decreases as the doping level is increased and exhibits anisotropy in the immediate vicinity of the transition. The effects of compensation and induced antiferromagnetic ordering on the g factor are analyzed. It is shown that, as the transition point is approached, the high-temperature limit of observation of the electron spin resonance rises sharply.

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)

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)

Anomalously intense dispersion has been observed in the magnetic resonance signals of manganese clusters in the chalcopyrite crystal ZnGeP 2 :Mn with a high concentration of manganese. The EPR signals detected correspond to at least two types of isolated manganese ions. One of these apparently possesses acceptor properties, which makes manganese a self-contained impurity for the formation of a ferromagnetic state in accordance with recent theoretical predictions.

Anomalously intense dispersion was observed in the magnetic resonance signals of manganese clusters in the chalcopyrite crystal ZnGeP2:Mn with a high concentration of manganese. The EPR signals detected corresponded to two types of isolated manganese ions. One of these apparently possesses acceptor properties, which makes manganese a self-contained impurity for the formation of a ferromagnetic state in accordance with recent theoretical predictions.

The effect of an elastic spontaneous distortion of the crystal lattice of a doped semiconductor Ge:As was observed near the insulator–metal (IM) phase transition. The effect was discovered in a study of the electron spin resonance at electron concentrations 0.8≤ n / n C ≤1 ( n C =3.7×10 17 cm −3 is the critical electron density for the IM phase transition) at low temperatures T ≤100 K. A study demonstrated that the phenomenon can be understood in terms of the Peierls model of a spin transition in the disordered spin system of the semiconductor. The spin-Peierls transition gives rise to a new type of defects in doped uncompensated or weakly compensated n-type semiconductor in the form of a domain structure.

The study of the electron paramagnetic resonance in Ge:As has revealed that the insulating state in uncompensated semiconductors is preserved near the insulator-metal phase transition because of the appearance of lattice distortions. The latter are caused by the interaction of the spins localized on impurity atoms due to the spin-Peierls transition. In Ge:As, this effect manifests itself in the concentration range n = n = 3 × 1017–3.7 × 1017 cm−3.

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.

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

Electron paramagnetic (EPR) and ferromagnetic resonance (FMR) have been studied in the system of (Zn,Mn)GeP2 ferromagnetic layer grown on undoped ZnGeP2 single crystal. Strong FMR signals are registered in the wide temperature range up to room temperature. EPR and photo-EPR of intrinsic defects are observed in ZnGeP2 substrate. EPR spectra characteristic of Mn2+ ions on Zn2+ sites in the bulk appear after the growth of the ferromagnetic layer on ZnGeP2 crystal indicating the efficient Mn-diffusion into the bulk crystal by the annealing treatments.

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.

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.

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 microwave low temperature magnetoresistivity of the low doped (nondegenerated) p-Ge was investigated with the use of the electron spin resonance technique. This technique permits to detect the derivative of the microwave absorption with respect to magnetic field and its change with this field. In our case, this change is proportional to the magnetoconductivity of the sample under investigation. Because of the averaging time of the effective masses of the light and heavy holes is much more then microwave frequency (10 GHz), this method permits to investigate the reaction of the each kind of the holes on the magnetic field separately. The experimental results are compared with the theory of the classical magnetoresistivity effect.

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.