L. Resnick

On the non-polarization and quasi-polarization spectroscopy of anisotropic media

Experimental distortions of the absorption contour shape, related to non-polarization spectroscopy of anisotropic media, have been considered. These distortions lead to incorrect results for three of the main spectroscopic parameters: intensity, half-width, and shape of the spectral contour. The distortions increase with increasing optical density but even for moderate density, they can be drastic and lead to artifacts. Such distortions can also occur in polarization spectroscopy if the vector E (or H for magnetic-dipole transitions) of the incident radiation is not properly matched to the vector of corresponding transition moment (quasi-polarization). Quantitative estimates for optical and magnetic-resonance spectra are presented, and compared with previous works.

Giant persistent photoconductivity induced crossover from strong to weak localization in Si-δ-doped GaAs compensated with Be acceptors

We present the results of measurements of two-dimensional electron transport in Si-δ-doped GaAs samples compensated with Be acceptors. It is shown that the temperature dependence of longitudinal resistivity Rxx in the interval 1K–100mK is well described by the variable-range-hopping mechanism Rxx(T)=R0exp[(T0/T)1/2] peculiar for strongly localized electrons. Transitional illumination of these samples by a red light causes a persistent photoconductivity (PPC), which is fully determined by irreversible increase of electron mobility. As a result of illumination, parameter T0 decreases which leads to a giant exponential increase of PPC at low temperatures. After high dose of illumination, the temperature dependence of conductivity changes from exponential to logarithmic law, which can be considered as a crossover from strong to weak electron localization.

Determination of the impurity concentration in heavily doped inhomogeneous semiconductors from the measurement of the low-temperature conductivity

A method has been developed for determining the effective concentration of shallow impuritiesN* reponsible for the low-temperature conductivity in the vicinity of the metal-insulator transition for inhomogeneous samples of n-Ge:As. The method is based on the measurement of two ratios of sample resistance γ-R(4.2 K)/R(300 K), β=R(2.0 K)/R(4.2 K) and the conductivity σ(4.2 K). The next step consists of plotting and σ(4.2) vs β. Assuming that β is the most reliable parameter, one can calculate, after an averaging procedare, the corrected values ofγ*,π*(4.2) and the resistivity at room temperatureρ*(300)=[γ*π*(4.2)]−1. Finally, using the known dependence ρ(300)=f(N) for homogeneous samples, one can obtain the values ofN*. The dependences ofN* on β and on γ are plotted. The scaling behavior of the conductivity of the Ge:As samples with corrected values ofπ*(4.2) andN* has been observed down toT=100 mK.