23 research outputs found
Determination of the parameters of semiconducting CdF2:In with Schottky barriers from radio-frequency measurements
Physical properties of semiconducting CdF_2 crystals doped with In are
determined from measurements of the radio-frequency response of a sample with
Schottky barriers at frequencies 10 - 10^6 Hz. The dc conductivity, the
activation energy of the amphoteric impurity, and the total concentration of
the active In ions in CdF_2 are found through an equivalent-circuit analysis of
the frequency dependencies of the sample complex impedance at temperatures from
20 K to 300 K. Kinetic coefficients determining the thermally induced
transitions between the deep and the shallow states of the In impurity and the
barrier height between these states are obtained from the time-dependent
radio-frequency response after illumination of the material. The results on the
low-frequency conductivity in CdF_2:In are compared with submillimeter (10^{11}
- 10^{12} Hz) measurements and with room-temperature infrared measurements of
undoped CdF_2. The low-frequency impedance measurements of semiconductor
samples with Schottky barriers are shown to be a good tool for investigation of
the physical properties of semiconductors.Comment: 9 pages, 7 figure
Spin Transistor and Quantum Spin Hall Effects in CdBxF2-x - p-CdF2 - CdBxF2-x Sandwich Nanostructures
Planar CdBxF2-x - p-CdF2 - CdBxF2-x sandwich nanostructures prepared on the
surface of the n-type CdF2 bulk crystal are studied to register the spin
transistor and quantum spin Hall effects. The current-voltage characteristics
of the ultra-shallow p+-n junctions verify the CdF2 gap, 7.8 eV, and the
quantum subbands of the 2D holes in the p-type CdF2 quantum well confined by
the CdBxF2-x delta-barriers. The temperature and magnetic field dependencies of
the resistance, specific heat and magnetic susceptibility demonstrate the high
temperature superconductor properties for the CdBxF2-x delta-barriers. The
value of the superconductor energy gap, 102.06 meV, determined by the tunneling
spectroscopy method appears to be in a good agreement with the relationship
between the zero-resistance supercurrent in superconductor state and the
conductance in normal state at the energies of the 2D hole subbands. The
results obtained are evidence of the important role of the multiple Andreev
reflections in the creation of the high spin polarization of the 2D holes in
the edged channels of the sandwich device. The high spin hole polarization in
the edged channels is shown to identify the mechanism of the spin transistor
and quantum spin Hall effects induced by varying the top gate voltage, which is
revealed by the first observation of the Hall quantum conductance staircase.Comment: 5 pages, 9 figure