Oscillatory Behavior during the Anodization of InP

Abstract

Spontaneous oscillations in current have been observed during anodization of InP. Oscillations were observed under three significantly different sets of conditions, potential sweep, constant potential, and constant current, for InP in an aqueous (NH 4 ) 2 S electrolyte. Their frequency was found to increase with increasing anodic bias and values in the range of 0.1 to 1.25 Hz were recorded. Frequency was proportional to current density regardless of whether the measurements were carried out during a potential sweep or at constant potential. Thus, the charge passed per oscillation remained constant. A characteristic value of ϳ0.3 C cm Ϫ2 was measured under potential sweep conditions, and a similar value was obtained under constant potential conditions. More complex oscillatory behavior was observed under constant current conditions. The current in the oscillatory region corresponds to the continuous growth of a thick porous film on the electrode.There have been a number of reports of oscillatory behavior during the anodization of semiconductor electrodes. Similar behavior has been observed on metal anodes and these fluctuations in current and potential have been reported under many different conditions and for many electrode/electrolyte systems, 1-6 such as Fe in H 2 SO 4 , HClO 4 , and H 3 PO 4 , Cu in H 3 PO 4 and acidic NaCl, and Ni in H 2 SO 4 . The observation of oscillations during the anodization of p-type 7 and n-type 8 Si has been reported mainly in fluorinecontaining electrolytes. Typically, oscillations occurred after the electropolishing region of potential and a thin surface film was present. 9 Several hypotheses 10,11 have been advanced but there appears to be no agreement on a general mechanism. There also have been reports of anodic oscillatory behavior for CdTe, 12 HgTe, 13 and CdHgTe 14 in sulfide solutions and for n-GaAs under conditions of strong illumination in a borax solution. 15 More recently, potential oscillations have been observed during galvanostatic anodization of n-InP in HCl. 16 Despite intensive research activities in this area, the origin of such oscillatory behavior is still unclear. The study of these oscillations is of fundamental interest and can be useful for obtaining information about interactions occurring at the electrode/ electrolyte interface.Here we report the first observation, to our knowledge, of current oscillations during anodization of an InP electrode. The oscillations were observed in the course of a study 17-19 of the InP/aqueous (NH 4 ) 2 S interface which is of interest due to its role in the sulfur passivation of InP in device fabrication. 20 ExperimentalThe working electrode consisted of ͑100͒-oriented monocrystalline sulfur doped n-InP with a carrier concentration of ϳ4 ϫ 10 18 cm Ϫ3 . An ohmic contact was made by alloying indium to the InP sample and the contact was isolated from the electrolyte by means of a suitable varnish. Anodization was carried out in a 3 mol dm Ϫ3 aqueous (NH 4 ) 2 S electrolyte. A three-electrode configuration was used for the el...

Electrochemical pore etching in germanium

“…25. However, in contrast to comparably well-developed voltage oscillations in the InP case [39,45,68] and very recent observations of oscillations coupled to self-organized pore structures in GaP [49,69], no structure formation or self-organization effects coupled to the voltage oscillations have been observed for the pores so far.…”

Electrochemical pore formation onto semiconductor surfaces

“…In the case of Si, dendritic growth following the h100i directions occurs [136]. Current oscillations have also been reported [140,141] but pore diameter fluctuations are not often synchronized. It is, however, possible to maintain the simultaneous pore variation established by a galvanostatic treatment in a following potentiostatic polarization [16].…”

Pores in III–V Semiconductors

“…[10] A whole chapter will be devoted to this issue. A special feature of self-organization in III±V compounds is the simultaneous occurrence of pore-diameter oscillations and external-voltage oscillations in InP and GaP [68,69] while voltage±current oscillations and pore formation were strictly separate issues in Si. [58] However, similar self-organization issues were now found in SiÐafter their discovery in the III±V materials triggered a systematic search.…”