Photoelectrochemical Etching and Removal of the Irregular Top Layer Formed on InP Porous Nanostructures

Abstract

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...

Realization of an extremely low reflectance surface based on InP porous nanostructures for application to photoelectrochemical solar cells

“…1(a), a disordered irregular layer formed and remained on top of the ordered porous layer after the first anodization. To remove this irregular layer, the porous surface was photo-electrochemically etched under illumination at an anodic bias of 1 V in the same electrolyte [12]. Figure 1(b) shows typical scanning electron microscope (SEM) images of the top view of the InP porous samples just after anodization and after photo-electrochemical (PEC) etching for 200 s (t PEC = 200 s).…”

Low Reflectance Surface Observed on InP Porous Structures after Photoelectrochemical Etching

“…A disordered irregular layer formed and remained on top of the ordered porous layer after the first anodization. To remove this irregular layer, the porous surface was then photo-electrochemically etched under illumination at an anodic bias of 1 V in the same electrolyte (12). Figure 1(a) shows typical scanning electron microscope (SEM) images of the InP porous sample after photo-electrochemical (PEC) etching for 200 s (t PEC = 200 s).…”

Large photocurrent-response observed at Pt/InP Schottky interface formed on anodic porous structure

“…To remove the irregular top layer, the porous surface was then photo-electrochemically etched at an anodic bias of 1.5 V in the same electrolyte under illumination [13]. After the irregular top layer was removed by the photoelectrochemical (PEC) etching, a cathodic bias was applied to a porous structure in a H 2 PtCl 6 electrolyte in order to form a thin platinum film on the wall inside the pores.…”