Cleber A. Amorim

Back-to-back Schottky diodes: the generalization of the diode theory in analysis and extraction of electrical parameters of nanodevices

We report on the analysis of nonlinear current-voltage characteristics exhibited by a set of blocking metal/SnO(2)/metal. Schottky barrier heights in both interfaces were independently extracted and their dependence on the metal work function was analyzed. The disorder-induced interface states effectively pinned the Fermi level at the SnO(2) surface, leading to the observed Schottky barriers. The model is useful for any two-terminal device which cannot be described by a conventional diode configuration.

Observation of persistent photoconductivity in vanadyl phthalocyanine

Persistent photoconductivity (PPC) in vanadyl phthalocyanine (VOPc) organic light-emitting diodes was investigated using photoconductive time response, photocurrent?voltage characteristics and charge extraction in linearly increasing voltage (CELIV) measurements. The experiments were performed in phase 1 (amorphous) and in phase 2 (crystalline) samples obtained by the physical vapour deposition (PVD) technique over ITO/glass electrodes with an Al covering electrode. The results indicated a photoconductivity with a long decay time in phase 1 VOPc described by a stretched exponential relaxation. The device showed a rectifying behaviour and the mobility of holes was measured by CELIV, following a dispersive model. In crystalline samples the PPC effect was not observed and the dominant mechanism of transport of holes was hopping in a Gaussian density of states.

Fluorine doped SnO2 (FTO) nanobelts: some data on electronic parameters

Fluorine doped SnO2 (FTO) nanobelts were synthesized and their transport properties, such as conduction mechanism, mobility, carrier density and density of states (DOS) were investigated. Variable range hopping was observed as the dominant mechanism in a large range of temperature (40?260?K). Through these data we estimated the localization length and hopping distance at 300?K of FTO nanobelts exhibiting a three-dimensional character for carrier transport. The carrier mobility was calculated to be 48?cm2?V?1?s?1 for samples with carrier density of 2???1018?cm?3. Taking into account the parameters obtained from temperature-dependent resistivity and the above data, the characteristic DOS at Fermi level in our samples was found.

Oxygen-induced metal-insulator-transition on single crystalline metal oxide wires

In this work we report on the transition from metal to insulator conduction of individual single crystalline In2 O3 wires induced by different oxygen concentration during their growth. The transport measurements revealed that the metallic conduction was mainly governed by the acoustic phonon scattering and the insulating character was addressed by the variable range hopping mechanism, which in turn can be considered as a first evidence of the occurrence of an Anderson-like metal-insulator-transition (MIT). The experimental data provided the critical carrier density to be 8×1018 cm-3 corresponding to a critical impurities spacing of 2.5 nm, which was found to be in agreement with previous reported data on polycrystalline indium oxide samples and with our recent finding on In2 O3 semiconducting samples. The approach presented here can be used to grow other metal oxide systems in which oxygen vacancies play a fundamental role for the electron transport features.

Measuring the mobility of single crystalline wires and its dependence on temperature and carrier density

Kinetic transport parameters are fundamental for the development of electronic nanodevices. We present new results for the temperature dependence of mobility and carrier density in single crystalline In(2)O(3) samples and the method of extraction of these parameters which can be extended to similar systems. The data were obtained using a conventional Hall geometry and were quantitatively described by the semiconductor transport theory characterizing the electron transport as being controlled by the variable range hopping mechanism. A comprehensive analysis is provided showing the contribution of ionized impurities (low temperatures) and acoustic phonon (high temperatures) scattering mechanisms to the electron mobility. The approach presented here avoids common errors in kinetic parameter extraction from field effect data, serving as a versatile platform for direct investigation of any nanoscale electronic materials.