Characteristics Of Amorphous Thin Films Research Articles

Electrophysical Properties of Ge–Sb–Te Thin Films for Phase Change Memory Devices

In this work, we studied temperature dependences of the resistivity and current-voltage characteristics of amorphous thin films based on the materials of a Ge–Sb–Te system of compositions GeSb4Te7 (GST147), GeSb2Te4 (GST124), and Ge2Sb2Te5 (GST225) applied in the phase change memory devices. The effect of changes in the composition of thin films on the crystallization temperature, resistivity of films in amorphous and crystalline states, and on the activation energy of conductivity is determined. It is found that the peculiarity of these materials is the mechanism of two-channel conductivity where the contribution to the conductivity is made by charge carriers excited into localized states in the band tails and by carriers of the delocalized states in the valence band.

Electrophysical properties of phase change memory materials on the pseudo-binary line GeTe-Sb2Te3

The temperature dependences of the resistivity and current-voltage characteristics of amorphous thin films on the basis of GeSb4Te7, GeSb2Te4, and Ge2Sb2Te5 perspective for the phase change memory application were investigated. It was revealed that two-channel conduction mechanism with the transport of charge carriers by the localized states in the valence band tail and delocalized states of the valence band is characteristic feature of these materials.

Transparent amorphous zinc oxide thin films for NLO applications

This review focuses on the growth and optical properties of amorphous zinc oxide (ZnO) thin films. A high quality ZnO films fabricated by dip-coating (sol–gel) method were grown on quartz and glass substrates at temperature equal to 350K. The amorphous nature of the films was verified by X-ray diffraction. Atomic Force Microscopy was used to evaluate the surface morphology of the films. The optical characteristics of amorphous thin films have been investigated in the spectral range 190–1100nm. Measurement of the polarized optical properties was shows a high transmissivity (80–99%) and low absorptivity (<5%) in the visible and near infrared regions at different angles of incidence. Linear optical properties were investigated by classic and Time-Resolved Photoluminescence (TRPL) measurements. Photoluminescence spectrum exhibits a strong ultraviolet emission while the visible emission is very weak. An innovative TRPL technique has enabled the measurement of the photoluminescence decay time as a function of temperature. TRPL measurements reveal a multiexponential decay behavior typical for amorphous thin films. Second and third harmonic generation measurements were performed by means of the rotational Maker fringe technique using Nd:YAG laser at 1064nm in picosecond regime for investigations of the nonlinear optical properties. The obtained values of second and third order nonlinear susceptibilities were found to be high enough for the potential applications in the optical switching devices based on refractive index changes. Presented spectra confirm high structural and optical quality of the investigated zinc oxide thin films.

Injection of holes and their localization in defect states at the interface between an electrochromically sensitive single crystal and an amorphous thin film of a complex tungsten oxide

The dynamic current-voltage and estance-voltage characteristics of amorphous thin films of complex tungsten oxides (tungsten oxide bronzes) and, for comparison, tungsten oxide bronze single crystals have been measured with a change in the character of their interaction with electromagnetic radiation. The optoelectronic properties of the samples have been analyzed taking into account the important role of the processes of hole injection, carrier localization in traps, and nanostructurization. A model of the physical processes occurring in the surface and near-surface regions at the interface between a tungsten oxide bronze and a liquid proton electrolyte, different from the generally accepted approach, is considered.

Transient conduction characteristics of amorphous thin films of Si12Te48As30Ge10 in the pre-switching regime

In the field-dependent conductivity region, the current transient exhibits a maximum after the initial displacement current spike. This maximum or cusp, and the subsequent decay of the current to a steady-state value are temperature-activated processes. When two identical voltage pulses are applied to the chalcogenide, the magnitude of the second current pulse is a function of the time interval between the two pulses. The recovery time describing this process is also temperature-activated. A tentative model invoking hole injection under space-charge-free conditions with a subsequent trap-limited drift motion of the injected carriers together with 'semi-permanent' trapping in deeper states, has been suggested to account for the observed behaviour. The trapping centres controlling the trap-limited drift mobility are located at approximately 0.5 eV below the Fermi level. The existence of a different 'deeper' type of capturing centre with a temperature-activated capture cross-section has been proposed as an explanation of the double-pulse experimental behaviour and the current decay following the cusp.