Investigation on the frequency‐dependence of the impedance of the nearly ideally polarizable semiconductor electrodes CdSe, CdS and TiO₂

Abstract

The impedance of several nearly ideally polarizable semiconductor electrodes (CdSe, CdS, TiO,) has been studied as a function of applied voltage and of frequency. The differential capacitance and resistance appear to obey to simple frequency laws. A mathematical model accounting for these laws is presented, in which a distribution of time constants is assumed, associated with dielectric relaxation phenomena in the double layer at the semiconductor/electrolyte interface. The experimental results indicate, that the source of the frequency-dependence has to be sought in structural irregularities of the surface region of the electrode. The proposed model appears to be also applicable to results, mentioned in the literature, concerning other semiconductor/electrolyte systems. The possibility of determining the flat-band potential from frequency-dependent capacitance data is discussed. Die Impedanz verschiedener fast ideal polarisierbaren Halbleiterelektroden (CdSe, CdS, TiO,) wurde in Abhangigkeit yon der angelegten Spannung und der Frequenz untersucht. Die Differentialkapazitat und der Differentialwiderstand zeigen einfache Frequenzabhangigkeiten. Diese Gesetze werden aufgrund eines mathematischen Modells gedeutet, in dem eine Verteilung von Zeitkonstanten angenommen wird, die mit dielektrischen Relaxationserscheinungen in der Doppelschicht an der Halbleiter/Elektrolyt-Phasengrenze in Zusammenhang stehen. Die Ergebnisse deuten darauf hin, Strukturdefekte im Oberflachengebiet der Elektrode seien fur die Frequenzabhangigkeit verantwortlich. Es zeigt sich, daO das vorgeschlagene Modell auch auf Literaturergebnisse betrefis anderer Halbleiter/Elektrolyt-Systeme anwendbar ist. Die Moglichkeit, das Flachbandpotential aus frequenzabhangigen Kapazitatsergebnissen zu bestimmen, wird besprochen.

Coulostatic pulse relaxation at the TiO2 (single crystal)/electrolyte solution interface

“…(iv) The fiat band potential values found on the basis of the assumption that changes in other potential drops can be neglected agree with values reported by other investigators (19,21,28).…”

Physicochemical Characterization of Passive Films and Corrosion Layers by Differential Admittance and Photocurrent Spectroscopy

“…71,72 In the case of c-SC the possible physical cause of such frequency dependence has been also attributed to the presence of an external (disordered or amorphous) layer, which after chemical etching of the surface of c-SC could be removed to restore the expected behavior. 73 In the case of thin passive film the presence of a frequency dependent differential capacitance is intrinsic to the formation of a layer having an amorphous or strongly disordered nature requiring the use of interpretative models accounting for such a specific feature. According to this it appears preferable to afford such a common aspect in the study of passive film/electrolyte interface by using a more general theoretical approach based on the theory of amorphous semiconductor Schottky barrier which is able to provide a better physical description also for the behavior of crystalline semiconductor junction containing a distribution of donor (acceptor) level in the forbidden energy gap of the SC.…”

On the fractal nature of frequency dispersion of the impedance of the interface tellurium/electrolyte

“…The experimental errors connected with boundary effect, streak effect, roughness of electrode surface etc. [16][17][18] were excluded in our work.…”

“…Additional polishing etching was done in conformity with the recommendation descn~ed in ref. [16]. The working area of the tellurium electrode constituted about 0.2 cm 2.…”