High-density formation of semiconductor nanostructures has been intensely researched for applications such as photonic crystals, quantum and optoelectronic devices, and chemical and biochemical sensors. In this study, we report a high-density array of size-controlled InP porous nanostructures formed by a two-step electrochemical process and their feasibility for the application to chemical sensors. Our process consists of the pore formation on a (001) n-type InP substrate and the subsequent etching of pore walls caused by changing the polarity of the InP electrode in a HCl-based electrolyte. By applying the anodic bias to the InP electrode, the high-density array of uniform pores was formed on the surface. The pores orderly aligned in a triangular lattice with a period of 130 nm and a wall thickness of 30 nm. In the depth direction, the pores were straightly formed over 80 mm with keeping good uniformity. These features are very similar to the Al2O3 porous structures. Next, the cathodic bias was applied to the porous sample to reduce the wall thickness by cathodic decomposition of InP. From the analysis using a scanning electron microscope (SEM), we found that the thickness of InP nanowall was precisely controlled in a range from 30 to 15 nm by changing cahtodic bias and time. This resulted in the formation of unique quantum nanostructures with a high aspect ratio that are not obtainable by other methods. From the electrochemical measurements on the InP porous nanostructuer, we found that the efficiency of some electrochemical reactions increased at the porous surface having the extremely large surface area. For example, the current-voltage characteristics of the porous sample showed larger response to the addition of a H2O2, as compared with the planar InP. This result indicates that InP porous nanostructures formed by the present process is very promising for application to amperometric chemical sensors.

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