Electrochemical Impedance Study of the Germanium/Electrolyte Interface

Abstract

In this paper, an electrochemical impedance study of the Ge/electrolyte interface has been carried out. At n-type Ge͑100͒ and Ge͑111͒ electrodes with different donor densities, linear Mott-Schottky plots were observed over a wide potential region, showing that the depletion region is conserved up to a band bending exceeding the bandgap of Ge. In most cases, the Mott-Schottky plots show some frequency dependence. A more elaborate investigation of the total interfacial impedance using electrochemical impedance spectroscopy shows that this frequency dependence may be caused by an additional impedance in parallel with the depletion layer capacity in the equivalent circuit describing the Ge/electrolyte interface. Under very weak depletion conditions, i.e., close to the flatband potential, an additional impedance is also observed, which may be related to electron-hole recombination at the semiconductor surface. For p-type Ge electrodes, linear Mott-Schottky plots are much more difficult to obtain, probably because electrochemical reactions and/or surface recombination strongly complicate the total impedance of the Ge/electrolyte interface.Due to the continuous downscaling of transistor sizes in accordance with Moore's law, Si-based devices are expected to run into performance limits. As a possible solution to this problem, germanium is put forward as a material for future high-speed transistors, because of its much higher charge carrier mobility as compared to Si. However, in order for the development of performant Ge transistors to be successful, some important drawbacks need to be resolved first, such as the problems with high n-type dopant activation and the stronger deterioration of channel mobility caused by interface states for a negative metal oxide semiconductor than for a positive metal oxide semiconductor. 1 Also, whereas very performant wet cleaning procedures have been developed for Si, these procedures do not seem to yield equally good results with Ge because of the apparent much higher reactivity of Ge toward etching agents. 2 Therefore, a more fundamental understanding of the Ge surface appears useful. As it is known that impedance measurements may yield more insight into some fundamental properties of the semiconductor surface and processes occurring at the semiconductor/ electrolyte interface, a detailed electrochemical impedance study of the Ge/electrolyte interface is described in this paper. The impedance of the Ge/electrolyte interface has been studied since the very early days of semiconductor electrochemistry. [3][4][5] In these studies, it was found that the capacitance of the Ge/electrolyte interface shows a minimum as a function of the potential, which, at least for intrinsic Ge, occurs at the flatband potential. Our results are compared to these measurements. ExperimentalMeasurements were performed on wafers cut from Czochralskigrown n-and p-type Ge crystals ͑Umicore, Olen, Belgium͒ with either ͑100͒ or ͑111͒ orientation. The p-type Ge͑100͒ was Ga-doped ͑resistivity between 0.020 and 0.026 ⍀ ...

Tailoring (Bio)chemical Activity of Semiconducting Nanoparticles: Critical Role of Deposition and Aggregation

“…CB and VB = conduction and valence band, respectively, E F = Fermi level. Positions of the band edge and Fermi levels are extrapolated from refs − assuming their Nernstian behavior.…”