K. Kyritsi

Intermittency in low frequency current oscillations in semi-insulating GaAs

Abstract Spontaneous low frequency current oscillations were observed in semi-insulating crystalline GaAs. If the value of the applied voltage U was increased, a crisis induced intermittency was observed. The time intervals between successive transitions were measured. For values of the control parameter U larger than a critical value two interacting chaotic subattractors were observed. The average time intervals are scaling with the control parameter with a critical exponent very close to −1/2.

High-frequency oscillations in an α-Si/Si(p)/Si(n) device

Abstract An α-Si/Si(p)/Si(n) heterojunction transistor exhibits current oscillations, which depending on the applied base–emitter voltage are either periodic or chaotic. The frequency dependence of the oscillations on the collector–emitter and the base–emitter voltage as well as on the load resistance, are presented.

Electrical properties of an a-Si/Si(p)/Si(n) heterojunction device

The electrical I-U characteristics of the three-terminal device a-Si/Si(p)/Si(n) have been investigated. The device shows both transistor and switching behaviour depending on the magnitude of the base current. The influence of the base current on the holding and switching voltages has been studied. A model describing this behaviour of the device has been suggested. It is based on the existence of a narrow region adjacent to the a-Si/Si(p) junction, characterized by an extremely high recombination rate of the injected carriers.

Growth and characterization of (SnS2)x–(SnSe2)1−x mixed crystals

Abstract (SnS 2 ) x –(SnSe 2 ) 1− x layered crystals were grown using the vertical Bridgman technique for x =0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.9, 1.0. IR-spectra of these compounds were obtained using a Bruker-spectrometer. The structural properties were studied using transmission electron microscopy (TEM). The variation of the structural and optical properties was studied as a function of the composition x .

Electron- and hole-mobility of Hg(BrxI1−x)2 crystals (x = 0.25, 0.50, 0.75)

Abstract The electron- and hole-mobility of Hg(BrxI1−x)2 crystals with compositions x=0.25, 0.50, 0.75 and 1.00 were measured using the time-of-flight method. The samples, in the form of thin layered plates, were irradiated with an 241 Am source; a memory oscilloscope monitored the corresponding current pulses created by the nuclear source. So the flight time and consequently the mobilities of the free electrons and holes were determined, and compared to results obtained on HgI2.

Current pulses and high-frequency oscillations in a-Si/Si(p)/Si(n) heterojunction device

A three-terminal a-Si/Si(p)/Si(n) heterojunction device was found to generate pulses of the collector current with a rise time of approximately 10-7 s and a fall time of approximately 4 ? 10-7 s. The voltage applied to the base (0.8-1.5 V) controlled the pulse repetition rate. When the voltage reaches ~1.0 V, the pulses start to overlap, and the output signal is a high-frequency oscillation (106-107 Hz) of the collector current. A simple mechanism explaining the pulse generation and the high-frequency oscillations has been proposed. It involves the extremely high recombination rate of the injected carriers in the thin a-Si layer of the a-Si/Si(p) interface.

The influence of Tl4Bi2S5 precipitates on the crystalline TlBiS2 properties

Crystalline TlBiS 2 having homogeneously distributed Tl 4 Bi 2 S 5 precipitates was grown by the vertical Bridgman technique in a two-step procedure. X-rays and Transmission Electron Microscopy (TEM) studies were used to identify the as-grown material whereas a Scanning Electron Microscopy (SEM) examination revealed its layered structure. The electrical conductivity σ was measured both along (σ | ) and across (σ⊥) its layers. IR reflectivity measurements were also performed and the plasma minimum was determined. Both electrical and optical characterization show properties similar to those of TlBiS 2 but a reduced N/m* ratio and an irregular voltage oscillation in the I-U characteristics were deduced. Combining the results from these investigations a possible explanation was proposed.

The period doubling route to chaos of the electrical conductivity in excited photoconductors

Abstract In the present report the generation of sinusoidal signals in a photoconductor subject only to dc excitations is considered. For this purpose the model of an n -type photosensitive semiconductor containing two localized levels in its energy gap is examined. For suitable constant illumination and constant applied electric field the semiconductor is exhibiting periodic or chaotic conductivity, if the two levels are sufficiently closed to each other. As the levels move apart the signal experiences the period doubling route to chaos.