J. Stupakova

Microwave detectors based on porous silicon

Two types of structures comprising porous silicon (por-Si) layers between metal electrodes were prepared, which possessed nonlinear (A type) and linear (B type) current-voltage characteristics. The exposure to microwave radiation leads to the appearance of an emf between electrodes. The B-type structures exhibit high voltage responsivity and can be used as microwave radiation sensors.

Electric properties of Y-Ba-Cu-O micro-diodes based on asymmetrically narrowed mesas

We present our studies of electric properties of micro-diodes based on asymmetrically narrowed, partially oxygen-depleted, semiconducting YBa2Cu3O7−x thin-film mesas. A level of asymmetry of nonlinear current-voltage characteristics of our diodes increases with the decrease of the residual oxygen content in their neck region and with increasing the operating temperature. The largest asymmetry is observed for diodes with x ∼ 0.5 and at T = 300 K. An asymmetric distribution of the electric potential for different bias polarities initiate an asymmetric, non-uniform distribution of intrinsic electric field due to heating of carriers in the diode. The experimental results and possible diodes technology are discussed.

Detecting microwave radiation on metal–porous silicon contacts

We have studied the rise of electromotive force (emf) across ohmic and nonohmic metal–porous silicon contacts under the action of 10-GHz microwave radiation. It is established that emfs of opposite polarities with different growth (and decay) rates are generated across the contacts of different types. The emf growth across the potential barriers of contacts is explained using a model of the microwave-induced heating of charge carriers. It is shown that the use of a porous semiconductor layer is a promising way to increase the voltage–power responsivity of microwave detectors and eliminate the “point contact” effects.

Detection of microwave radiation on porous silicon nanostructures

We report on possibility to detect pulsed microwave radiation across the metal/oxide/porous silicon structures and analyse possible physical reasons causing the rise of the emf voltage signal. The n-type porous layers were fabricated according to conventional electrochemical etching procedure, and were exposed to pulsed 10 GHz microwave radiation. The results of investigation show that the porous Si samples have higher by at least one order voltage-to-power sensitivity than the samples without the porous layer, and are considered to have high potential to increase it further. Free carrier heating phenomenon is considered to be responsible for the signal formation.

Formation of surface morphology of silicon solar cells by means of two-step photo-electrochemical etching and their characterization

The electrochemical etching of porous silicon offers many diverse opportunities for production of complex porous silicon structures located not only on the surface but also in a bulk of the silicon devices. A specific technological regime, the photo-electrochemical etching can affect bulk of the silicon device but at the same time saving its textured surface almost unchanged. Our group is the first who investigated the silicon solar cells with textured surface modified by means of photo-electrochemical etching. Etched devices demonstrated better photoelectrical characteristics if compare ones with unmodified solar cells. Our current work presents results on research of solar cells photoelectrochemically treated in HF: ethanol solution. Applied etching regime allowed us to modify the emitter’s volume at the same time affecting only minimally the surface of the solar cell itself. SEM micrographs show the elevations, ripples, bumps, cracks etc. on the surface of photo-electrochemically treated solar cells. The optical ellipsometer spectra, optical microscope measurements results, SEM micrographs of surface morphology as well as light reflectivity of the photoelectrochemically treated and untreated surfaces of the solar cells investigated and discussed in this work.

Effect of strong electric field on electrical characteristics of two-terminal porous silicon structures

Two-terminal diode-like porous silicon structures have been investigated under the impact of strong electric field. Strong electric field I-V current-voltage characteristics have been measured in pulse regime by applying electric pulses of 15 ns duration, at repetition rate of (100-150) Hz, creating average electric field in the structure up to (103-104) V/cm. Modification of structured state of the structures have been revealed at strong electric field influence, resulting in change and stabilizing of their series resistance.