A photoelectrochemical ͑PEC͒ process was developed to remove the irregular top layer from InP porous nanostructures. After anodic formation of a nanopore array, the PEC process repeated in the same electrolyte under illumination. The etching rate of the pore surfaces was strongly associated with their structural properties, being greater in the irregular top layer. The irregular top layer was completely removed by monitoring and controlling the anodic photocurrents in the ramped bias mode. © 2008 The Electrochemical Society. ͓DOI: 10.1149/1.2844216͔ All rights reserved.Manuscript received December 11, 2007. Available electronically February 20, 2008 A lot of research has been devoted to producing high-density arrays of nanostructures due to both their applications to future quantum electronic and optoelectronic devices and to downsizing chemical and biochemical sensors.1 The porous structure formed by the electrochemical anodic process is one of the more promising building-block candidates of the aforementioned devices. The porous alumina made from aluminum films has particular promise 2,3 because of its unique nanohole array structures, which are formed in a self-organized manner, and has been used as a template for various devices. The direct formation of porous structures has also been reported on semiconductor materials such as Si, [4][5][6]7,8 GaP,9,10 InP, 11-13 GaN, 14 and CdSe. 8 The structural properties and their tunability have been intensely investigated on III-V materials in an effort to improve electrical and optical properties.We recently succeeded in anodically forming arrays of straight nanopores on n-InP͑001͒ substrates. [15][16][17] The nanopores were laterally separated by InP nanowalls several tens of nanometers thick and formed in a straight vertical direction greater than several tens of micrometers. We previously reported that pore diameter and wall thickness can be controlled by adjusting the electrochemical anodic and cathodic conditions. 17 However, a disordered irregular layer usually forms during the initial stage of pore formation and partly remains on top of the ordered porous layer. Because this irregular layer has a thickness in the range from a few hundred nanometers to several micrometers, it degrades electrical and optical properties. Thus, complete removal of the irregular top layer has been one of the key issues in wide application of porous nanostructures for semiconductors.We report here on a photoelectrochemical ͑PEC͒ process developed to completely remove the irregular top layer from the InP porous surfaces. The PEC process can be repeated continuously after porous structures are anodically formed in the same electrolyte. Our present approach is much simpler and more controllable than other methods such as dry etching and conventional chemical etching.Our PEC process is schematically shown in Fig. 1a. The template porous structures were first formed by an anodic reaction in the dark, 16 and then the porous surface was photoelectrochemically etched in the same electrolyte...

The electrocatalytic activity of n-type InP porous nanostructures was investigated in terms of their application to amperometric biochemical sensors. The current sensitivities for H 2 O 2 detection were strongly dependent on the structural properties of these porous We demonstrated the direct detection of H 2 O 2 amperometrically by using porous nanostructures formed on highly-doped n-type InP substrates. We recently succeeded in electrochemically forming arrays of straight nanopores on n-InP (001) substrates. [11][12][13][14] The nanopores were laterally separated by InP nanowalls several tens of nanometers thick, and formed along a straight vertical direction more than several tens of micrometers. In addition to this, n-type InP has attracted attention as a sensor material due to the well-known surface sensitive nature of InP.

The electrochemical functionalization of n-type InP porous nanostructures and their feasibility for biochemical sensor applications were investigated. The porous structures have extremely large surface areas, i.e., over 10 m 2 /cm 3 , and superior electrical properties with conductive semiconductor substrates. As a first attempt at electrochemical functionalization, we successfully deposited a glucose oxidase ͑GOD͒ membrane onto an InP surface under an applied anodic bias of 1.2 V. With the addition of glucose, the response currents on the porous electrodes increased compared to those on planar InP electrodes due to their enlarged surface area. The sensitivity curves of the porous electrodes we used showed good linearity between the response currents and concentrations in a range from 0 to 5 mM.

In this paper, we demonstrated that the InP-based open-gate FET worked well as a liquid-phase chemical sensor in acid electrolytes. The open-gate FET clearly exhibited current saturation and pinch-off behavior in the electrolyte, resulted in a rapid response to the gate bias applied via the electrolyte. A series of sensing measurements showed that the surface potential of the InP linearly changed with the pH values of the electrolytes, and their sensitivity was strongly dependent on ion species contained in the electrolyte.