Electrochemical Pore Formation in InP: Understanding and Controlling Pore Morphology

Abstract

Pores formed anodically in InP at different temperatures, electrolyte (KOH) concentrations, carrier concentrations and current densities exhibit significant pore width variations. The pore width decreases as the temperature, carrier concentration or current density are increased. The pore width also decreases when the KOH concentration is increased up to 9 mol dm -3 , but increases slightly as the concentration is increased further. These pore width variations are explained by a three-step model for pore formation based on competition in kinetics between the different steps in the etching mechanism. The variation of pore width with current density is explained explicitly in terms of the crystallographic etching mechanism and this is supported by observation of the different crystallographic features of the pore cross section at different current densities.

Anodic Formation of Nanoporous Indium Phosphide in KOH Electrolytes: Effects of Temperature and Concentration

“…Each pit leads to a porous domain and, as the domain expands, it blocks the formation of etch pits in that region because the entire domain, including the surface above it, becomes depleted of carriers (with the exception of the pore tips). 61 Essentially then, there is competition between increasing potential, which enables pitting at sites with increasing values of E i , and current-related expansion of porous domains which prevents pitting in the vicinity of existing porous domains; the rate of increase of potential (scan rate) is constant for all experiments but the current is temperature-dependent. As can be seen from Fig.…”

“…9 where both pore width and pit width are plotted against layer thickness. It is possible 2,61 that the mechanism that controls pit width is to some degree similar to the mechanism which controls pore width and this would explain the correlation between them. Consequently, layer thickness is expected to be correlated with pore width since, as explained above, layer thickness is correlated with pit width.…”

“…We have previously proposed 2,6,61 that this model can also explain the variation in porous layer characteristics under different formation conditions. In this paper, we describe anodic etching experiments on n-InP in aqueous KOH under a variety of conditions of temperature and KOH concentration and present a comprehensive analysis of the results in terms of the three-step model.…”

“…1 The formation of crystallographically oriented (CO) <111>A pores suggests that etching is controlled by the relative rates of the surface reactions at different facets and any satisfactory model of electrochemical pore formation must explain how this can occur even though the rate-determining process (hole generation) occurs only at pore tips. To reconcile these requirements, we have proposed 2,61 a three-step model. The three steps are (1) hole generation at pore tips, (2) hole diffusion and (3) electrochemical oxidation of the semiconductor to form etch products, as shown schematically in Fig.…”

Forming the low­porous layers of indium phosphide with the predefined quality level

“…However, the dependence on the concentration of acid in a solution of electrolyte was not determined. In research [40], it is reported that dimensions of pores are influenced by various factors, including etching condition and characteristics of the original crystal. However, these data are insufficient to reveal common mechanisms of pore formation and establish the conditions, under which formation of porous structures with specified properties becomes possible.…”