Light induced oscillating reactions of silicon in ammonium fluoride solutions. Part 1. Simultaneous photocurent and excess microwave reflectivity measurements

For the first time, simultaneous photocurrent, I ph , and excess microwave reflectivity, m w , profiles are recorded during the light induced oscillatory behaviour of n Si 111 in aqueous ammonium fluoride solutions. Stationary oscillations in I ph , and m w are complementary to each other with maxima of I ph at minima of m w and vice versa. At higher positive potentials, irregular oscillatory behaviour is found and the complementarity of the signals is not fully maintained. For the initial time regime a model is suggested tentatively to determine electronic interface parameters from the simultaneous measurement of I ph and m w . For increased time, the oscillatory behaviour has also been evaluated with respect to surface recombination and charge transfer processes. In this time region, however, the application of the model suggested is problematic, as changes in band bending, trapping of charges and space charge layer recombination are not accounted for. For the observed lowest quantum yields gt; 0.2, it is assumed that the drift velocity is not the limiting facto

Microwave photo electrochemistry new insight into illuminated interfaces

Simultaneous potential dependent measurement of photoelectrochemical currents and of photoinduced microwave conductivity PMC allows the evaluation of a series of interfacial parameters eg charge transfer rate, surface recombination rate, surface minority carrier concentration , but relies on the validity of a relatively complicated theoretical analysis given in a preceding publication . It is now supported by providing a numerical calculation of the problem, which also describes PMC signals in the accumulation region. Experimental data obtained with n and p type silicon are further evaluated. Measurement of potential dependent PMC signals of n WSe2 interfaces in contact with complexing I amp; 8722; and non complexing redox agents Fe2 demonstrates charge transfer inhibition with non complexing redox species causing a damming up of minority carriers towards the interface. Spectral and time dependences ZnO and Si, WSe2, respectively of PMC signals are also discusse

Ellipsometric and microwave reflectivity studies of current oscillations during anodic dissolution of p-Si in fluoride solutions

Periodic current oscillations during anodic dissolution of monocrystalline p-Si(100) in buffered ammonium fluoride solutions (0.1 mol dm(-3) fluoride, pH 4.5) were investigated using a flow cell in order to eliminate mass transport limitations. The flow cell was designed to permit simultaneous in-situ ellipsometry, impedance and potential modulated microwave reflectivity measurements. Analysis of the ellipsometric response showed that the current oscillations are accompanied by a synchronous variation of the overall oxide thickness with an amplitude of 4.5 +/- 0.1 nn. Analysis of the relationship between the total oxide thickness and the current during the oscillation cycle shows that to a first approximation the rate of chemical dissolution of anodic oxide remains constant. Oscillations of the electrode admittance and potential modulated microwave reflectivity were also measured. The imaginary component of the admittance is related to the oscillation in thickness of a narrow inner region of 'dry' oxide and to changes in the accumulation capacitance. The oscillation in the potential modulated microwave reflectivity is interpreted in terms of the changes in the density of holes accumulated at the p-Si \ SiO2 interface