Peter Janietz

On capacity measurements and the energy distribution of surface states at the electrolyte-GaAs interface

Abstract The frequency-dependent values for the capacities obtained for GaAs, GaAsP and GaP were interpreted by means of the usual equivalent circuit with the capacity of the surface states and that of the depletion layer in parallel. Consistent results are obtained only assuming a continuous energetic distribution of surface states in the forbidden gap. Adsorption of a dye and Ru3+ leads to an altered distribution function, the maximum appearing can be accounted for by superimposing a Lorentz function on the cosh type of function. The dye adsorption was determined radiochemically and obeys a Freundlich isotherm. Ellipsometric measurements under the same conditions suggest the formation of non-passivating surface films in the electrolytes used.

Ruthenium-induced surface states on n-GaAs surfaces

Studies were conducted to investigate the properties of the Ru-GaAs interface. An analysis was made of two sets of experimental findings, namely the distribution of surface states of GaAs covered by submonolayers of ruthenium, as well as of electrical measurements on Ru-GaAs contacts. It was found for the present case that a deep state near E t , ≈ 0.3 eV above valence band maximum is induced at the surface. Thus the influence of the intrinsic defects is at least compensated. Using a simple model, it was investigated to which degree surface states and their energy would govern the barrier height. It was further studied how Fermi level pinning depends on the doping concentration of the semiconductor.

Zur elektrochemischen lumineszenz an halbreitern

Abstract The electrochemical luminescence of aromatic compounds in aprotic solvents was investigated using the following semiconductor electrodes: n-GaP, n-ZnO and n-SnO 2 . Electrochemical luminescence by direct heterogeneous electron transfer to the excited singlet or triplet state and subsequent luminescence could in no case be detected. The discussion of the mechanism of the redox processes involved is based on experimental observations and energetic correlations which were partly obtained by measuring the capacity of the semiconductor—solvent systems used. We presume that the directly excited states are deactivated by radiationless transitions due to a heavy atom effect. This conclusion was confirmed to the extent that the naphthalin luminescence was quenched by these semiconductors at 77 K.

Point of Zero Net Adsorbed Charge of Gallium Arsenide

For powdered GaAs the point of zero net charge at the inner Helmholtz plane has been determined to be about 5.9. To account for the discrepancy between this experimental value and a theoretical one based upon a relation between the electron affinity and the flatband potential of GaAs, interface states and dipole contributions to the potential difference across the semiconductor/electrolyte interface have been invoked. By reinvestigating the dependence of the flatband potential on redox couples added to the solution, convincing interface state densities have been found, which indeed bring the theory in accordance with experiment

On surface conductance measurements at the GaAs/electrolyte interface

Abstract An experimental setup and conditions for measuring the surface conductance of GaAs are described. The potential dependence of the conductance shows that an inversion layer is not formed; instead, the phenomenon of deep depletion is observed. By applying the theory of the Schottky contact, a relationship similar to the Mott-Schottky equation is derived for the conductance. A suitable plot may be used to determine flatband potentials accurately and, provided the mobility is known, the dopant concentration. The mobility may also be calculated from layer conductance measurements. Finally, the cause for the observed negative shift of the flatband potential when species containing large organic cations are adsorbed, is discussed.

Der einfluss des physikalisch-chemischen Oberflächen-zustandes einer Ag-Elektrode auf den Mechanismus und die Geschwindigkeit der elektrochemischen Reduktion von Perbenzosäure

Zusammenfassung Die Untersuchungen ergaben, dass an einer mit chemisorbiertem Sauerstoff bedeckten Ag-Elektrode der elektrochemischen Durchtrittsreaktion die dissoziative Chemisorption der Perbenzosaure in 2 radikalische Teilchen vorgelagert ist. An einer mit einer dunnen Ag 2 O-Schicht bedeckten Ag-Elektrode kommt es zu keiner vorgelagerten dissoziativen Chemisorption der Perbenzosaure. Die Grunde fur dieses verschiedenartige Verhalten werden anhand fruher entwickleter Vorstellungen uber die katalytische Wirksamkeit von an Ag chemisorbiertem Sauerstoff gedeutet. Die Auswertung der Versuchsergebnisse ergab weiterhin einen starken Einfluss des physikalisch-chemischen Oberflachenzustandes der Elektrode auf die Geschwindigkeit der elektrochemischen Durchtrittsreaktion, die an einer Ag 2 O-bedeckten Elektrode grosser ist als an einer mit chemisorbiertem Sauerstoff bedeckten Ag-Elektrode. Eine Erklarung fur diese Erscheinung war auf Grund des vorliegenden experimentellen Materials noch nicht moglich.