É. A. Lebedev

Optical and electrical properties of porous gallium arsenide

Photoluminescence (PL), Raman scattering, and carrier transport have been studied for the first time in porous GaAs prepared on (111) oriented wafers of n-type crystalline GaAs (faces A and B). Peaks of the main PL band from faces A and B were observed at 1.82 and 1.88 eV, respectively. The electron drift mobility was found to be ∼4×10−4 cm2 V−1 s−1. The nanocrystallite size in porous GaAs was determined both from PL spectra and from the Raman shift. The obtained values are close or equal to 6–8 nm.

Conductivity of layers of a chalcogenide glassy semiconductor Ge2Sb2Te5 in high electric fields

Effect of high electric fields on the conductivity of 0.5-1-µm-thick layers of a chalcogenide glassy semiconductor with a composition Ge2Sb2Te5, used in phase memory cells, has been studied. It was found that two dependences are observed in high fields: dependence of the current I on the voltage U, of the type I ∝ Un, with the exponent (n ≈ 2) related to space-charge-limited currents, and a dependence of the conductivity σ on the field strength F of the type σ = σ0exp(F/F0) (where F0 = 6 × 104 V cm−1), caused by ionization of localized states. A mobility of 10−3–10−2 cm2 V−1 s−1 was determined from the space-charge-limited currents.

Optical and electrical properties of polyamide acid and metal-polymer complex based on terbium

The basic optical and electrical properties of polyamide acid and its complex with Tb+2 have been studied. The occurrence of room-temperature photoluminescence (PL) with an emission peak at 520 nm is established. The activation energy of conductivity at temperatures above 350 K is 2.1 eV. Polyamide acid is comparable in PL intensity with an electroluminescent polymer, poly(p-phenylvinylene).

Transient current in amorphous, porous semiconductor-crystalline semiconductor structures

The time-of-flight technique in the weak signal mode (i.e., under conditions of small charge drift in the sample) is used to study the transient photocurrent in amorphous (porous) semiconductor-crystalline semiconductor structures. Amorphous Se-As materials, porous Si, and crystalline Si and CdSe were incorporated in the structures. The carrier drift mobilities in the amorphous and porous layers of the structures were determined. The appearance of a cusp on the curves of the transient current is shown to be caused by acceleration of carriers passing through the interface between the amorphous (porous) layer and the crystal. It is established that the carrier acceleration influences the drift mobility and the dispersion parameters.

Charge Carrier Transport in a Structure with Silicon Nanocrystals Embedded into Oxide Matrix

Current-voltage characteristics of Al/SiO2/c-Si structures with silicon nanocrystals (nc-Si) in the oxide layer are studied in a wide temperature range. The analysis based on the experimental data has shown that thermostimulated tunneling via electron states in nc-Si is a most probable mechanism of charge carrier transport in these structures.

Current instability with an S-shaped I-V characteristic in films of a metal-polymer complex of polyamide acid with Tb+2

The manifestation of current instability as an S-shaped I-V characteristic was detected in thin films of a metal-polymer complex of polyamide acid with Tb+2. The current instability characteristics are comparable to those of the switching effect in chalcogenide glasses. The origin of the current instability in the metalpolymer complex may be related to electrothermal switching. The threshold voltage and current in films ∼0.1 µm thick are 3–7 V and (2−1)×10−2 A/cm2, respectively.

Phase transitions occurring in glassy chalcogenide semiconductors induced by electric field or laser pulses

Order-disorder phase transitions in thin films of glassy chalcogenide semiconductors of the system Ge-As-Te, which take place during times on the order of microseconds in micron-sized volumes, have been studied and analyzed. The relationship between the reversible structural transitions induced by laser light pulses and the reversible semiconductor-metal transition taking place in a strong electric field is discussed. It is shown that the film can be taken repeatedly through a reversible phase transition in the conductivity at ∼500–600 K, as previously established. It has been shown that repeated transition from the crystalline to the glassy state is possible without destruction of the material for a wide range of power levels for durations of the laser light pulse less than a few microseconds, and that this fact plays a decisive role in the reversible structural transformations. It is shown that the existence of such a range of power levels is attributable to overheating.

Luminescence and electrical conductivity of polyamide acid and its metal-polymer complexes with La and Tb

The photoluminescence and electrical properties of organic semiconductors of polyamide acid (PAA) and its complexes with lanthanides are investigated. On the addition of La and Tb to PAA, the emission intensity increases by 40%. No inherent bands of lanthanides are found in the emission spectrum. The current-voltage characteristics and the temperature dependence of the conductivity of PAA and its complexes are investigated for layers ranging from 40 to 0.1 μm in thickness. A specific feature of its electrical properties is a hysteresis of the temperature dependence of conductivity with an increase or decrease in temperature. A considerable deviation of the current-voltage characteristics from linearity, which is associated with injection currents, is observed for layers 0.1–0.2 μm thick. The breakdown voltage and limiting-current density for these layers are 3–8 V and (2−1) × 10−2 A/cm2, respectively. The obtained value of the current density is comparable with the current density in layers of electroluminescent conjugate polymers at the same voltages.

Space charge limited current in porous silicon and anatase (TiO2)

A comparative study of the transient space-charge-limited current in porous silicon and porous anatase (TiO2) has been carried out. The room-temperature drift mobilities of electrons in porous silicon and porous anatase, determined from the transit times, are, respectively, 10−2 and 5×10−6 cm2 V−1 s−1. The specific features of space-charge-limited currents in porous anatase are discussed.

Drift mobility of carriers in porous silicon

The drift mobility of carriers in porous silicon has been studied in a wide temperature range (190–360 K) at electric field strengths of 2×103–3×104 V/cm. An exponential temperature dependence of the hole drift mobility with an activation energy of d ∼ 0.14 eV was established. The density of localized states controlling the transport is evaluated.