High‐Amplitude versus Low‐Amplitude Current Oscillations during the Anodic Oxidation of p‐Type Silicon in Fluoride Containing Electrolytes

Abstract

Sustained electrochemical oscillations at p-type Si(100) in a dilute ammonium fluoride electrolyte are investigated by means of ellipsometric intensity and hydrogen measurements. Two main types of oscillations are identified, one with a low and one with a high current amplitude. It is demonstrated that the low-current amplitude oscillations do not involve any variations in oxide quality or etch rate. Furthermore, experimental results suggest that the high-amplitude current oscillations emerge from the low-amplitude current oscillations and thus share the feedback loops causing the oscillatory instability. Hence, the origin of oscillations during anodic dissolution of silicon has to be reconsidered.

On the Origin of Damped Electrochemical Oscillations at Silicon Anodes (Revisited)

“…This is qualitatively fully consistent with our own and Lehmann's mechanical observations accompanying the transitions, as shown in Figure 1. [23] A relevant additional experiment in this respect is shown in Figure 10, which aims to address the effect of an imposed, intermittent oxide depolarisation during the anodic growth process. Figure 9 illustrates that this is indeed verified for the first two transitions at all different current densities being tested.…”

“…We thereby tend to be in line with a recent study suggesting that the oscillations do indeed have an electrical origin, rather than a morphological one. [23] A relevant additional experiment in this respect is shown in Figure 10, which aims to address the effect of an imposed, intermittent oxide depolarisation during the anodic growth process. In this experiment, the anodic current (set to yield j = 0.10 mA cm À2 ) was switched off at about 16 V (or 11 nm), that is, well before the first spontaneous oscillation would occur, and the subsequent voltage decrease during oxide depolarisation was recorded.…”

Electro-oxidation of p-silicon in fluoride-containing electrolyte: a physical model for the regime of negative differential resistance

“…The model is described and defined in Section 3. In Section 4 the predictions of the model are compared to the experimental data which we obtained from cyclic voltammmetry, ellipsometry, and dynamic multi-frequency analysis as well as to values of the dissolution valence from the literature [21,22,5]. Finally, we conclude the paper in Section 5.…”

“…When a silicon electrode is electrochemically dissolved in a fluoride containing electrolyte, it is covered by a layer of silica which can change its thickness in peculiar spatio-temporal patterns [1,2,3,4,5,6,7,8]. (For a comprehensive overview of the work until 2003 see Chapter 5 in [9].)…”

“…The central idea of our model is that the oxide is etched with a rate that depends on its composition. This assumption was motivated by measurements of dissolution valence [21,22,5], measurements of the current voltage characteristics, and by the fact that the etching is likely to occur purely chemically, i.e. without charge transfer [24,21,25].…”