Anodic Behavior - Electrochemistry of Silicon and Its Oxide - page 212

with current. 676,950 The infrared absorption, microwave reflectivity, electrode admit-
tance, hydrogen evolution, photocurrent, surface roughness, and electron injection
during the current oscillation are found to also oscillate in the same frequency as the
current oscillation. 408,602,855,862,1100,1116
5.10.3. Mechanisms
A number of models have been proposed for the mechanism of current oscilla-
tion on silicon electrode. A brief description of the major models is given below.
Lewerenz and Aggour 544,860,1100,1116 attributed the oscillation to the opening and
closing of the pores or point defects existing in the oxide film. The point defects are
formed at the oxide/silicon interface and develop into pores by selective etching of the
defects by HF. The opening of the pores then results in an increase in current which
forms oxide film at the bottom of the pores. The current decreases when the oxide film
grows in thickness until new sites of pores open up resulting in a sudden current
increase.
Cattarin et al . 855,862 measured the concentration gradient in the diffusion layers of
the electrolyte near the surface. They postulated that the rapid transition of electrode
potential from high to low is associated with a structural modification of the compact
oxide layer resulting in an increased etching rate of the oxide film. The fact that the
minimum thickness occurs at the maximum potential and maximum thickness at the
minimum potential suggests the formation of two types of oxide films: one type requires
a higher field to grow and is more compact than the other type, and the phase transi-
tion between them occurs at a certain film thickness.
Ozanam et al . 949,951 considered current oscillation to originate in the lateral
variation in the surface oxide film at the microscopic level. They proposed a
microdomain model in which the electrode surface is viewed as a collection of adja-
cent, self-oscillating areas. In a steady-state condition the contributions of the various
domains to the total current are completely uncorrelated. But on a potential excitation
these contributions are synchronized giving rise to the oscillation phenomenon. The
physical origin of the microscopic oscillation is considered to involve the defects in the