A. I. Veinger

Radiation defects in n-4H-SiC irradiated with 8-MeV protons

Capacitance methods and electron spin resonance (ESR) were applied to study deep centers in n-6H-SiC irradiated with 8 MeV protons. Schottky diodes and p-n structures grown by sublimation epitaxy or commercially produced by CREE Inc. (United States) were used. The type of the irradiation-induced centers is independent of the material fabrication technology and the kind of charged particles used. Irradiation results in an increase in the total concentration of donor centers. The possible structure of the centers is suggested on the basis of data on defect annealing and ESR.

Distinctive features of the magnetoresistance of degenerately doped n-InAs and their influence on magnetic-field-dependent microwave absorption

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.

Electron spin resonance of interacting spins in n -Ge: II. Change in the width and shape of lines

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.

Specific features of electron spin resonance in 4H-SiC in the vicinity of the insulator-metal phase transition: II. Analysis of the width and shape of lines

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.

Special features of electron spin resonance in 4H-SiC in the vicinity of the insulator-metal phase transition: I. Effects of spin interaction

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.

Anomalous Positive Microwave Magnetoresistance of Compensated Ge:Ga near the Metal–Insulator Transition

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 .

The magnetoresistance of compensated Ge:As at microwave frequencies in the vicinity of the metal-insulator phase transition

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.

Detection of impurity diamagnetic susceptibility and its behavior in n-Ge:As in the region of the insulator–metal phase transition

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.

Determination of the magnetic susceptibility of “poor” conductors by electron paramagnetic resonance

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.

Magnetic-Field-Dependent Microwave Absorption in HgSe in Weak Magnetic Fields

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.