arXiv subjects

B. Vainas

Publications and source records attributed to B. Vainas.

3 recordsLinked to original sources

arXiv2015

Large, light-induced capacitance enhancement in semiconductor junctions simulated by capacitor-resistor nets

The equivalent circuit simulation of random resistors-capacitors (R-C) net, modified to include large capacitors interfacing between the random R-C bulk and the electrode surface, shows an enhancement of 3 orders of magnitude of the apparent real dielectric constant at low frequencies upon an introduction of resistors percolating paths in the bulk. The appearance of the bulk R-percolating paths can represent the photo-generated high conductivity state of semiconductors bulk, an effect supported by the experimental observation that, in parallel with the photo-enhancement of the real dielectric constant, its imaginary part is strongly enhanced as well. The addition of the photo-generated charge carriers strongly enhances bulks electrical conductivity, effectively confining the space charge region to the interface between bulks edge and the electrode. That could be a simple phenomenological explanation for the apparent dielectric constant enhancement upon illumination in photocells, not involving elaborate physical models.

cond-mat.mtrl-sci↗

arXiv2014

1/f^s noise from random R-C networks driven by white noise current, with low frequency characteristics changed by percolation

A model based on thermal fluctuations in conductors in random resistor-capacitor (R-C) networks has been shown to generate a 1/f^s noise with s in between 0 and 1, while in many real systems the noise exponent is between 0 and 2. The wider range of noise exponents is shown here to be generated using a model of random R-C networks driven by white noise current source, and having different compositions of resistors and capacitors. C-rich networks approach a brown noise, 1/f^2 response, while R-rich networks approach a white noise, 1/f^0 response. Random R-C networks containing equal numbers of resistors and capacitors generate the classic, 1/f pink noise. Thus, the composition unbiased R-C networks produce the ubiquitous 1/f noise. Below a limiting frequency, which is a function of the size of the network, the values of individual R and C elements, and their relative numbers in the network, the power-law frequency AC response of the network no longer holds, and the 1/f^s noise response, turns into either capacitor (1/f^2), or resistor (1/f^0) response, depending on the nature of the persistent conductivity structures: series R-C pathways, or pure C and R percolation pathways.

cond-mat.mtrl-sci↗

arXiv2005

Simulation of the transient photocurrent response of polycrystalline photocells based on equivalent circuit analysis

We propose an equivalent circuit representation of the photogenerated charge separation and propagation in dye sensitized polycrystalline semiconductor in contact with a redox electrolyte. The suggested equivalent circuit for this type of photocell is based on an electrical transmission-line, and uses distributed photodiode model for the semiconductor-redox electrolyte interface. It was found that for small signal conditions, diodes can be replaced by equivalent elements, each consisting of a resistor and a capacitor connected in series. The equivalent circuit also provides for Beer-Lambert characteristics of light absorption. The simulation of the transmission line equivalent circuit, subjected to short pulse illumination, allows us to reproduce the experimentally found difference between the photocurrent responses of the photocell to illumination from the electrolyte side, and its response to illumination through the semitransparent back electrode, to which the polycrystalline semiconductor layer is attached. We suggest an electrochemical model for photogenerated charge separation, whereby the electrical field across the Helmholtz electrostatic double layer at the polycrystalline phase - electrolyte interface separates the photogenerated carriers.

cond-mat.mtrl-sci↗