Electrochemical Formation of Size-Controlled InP Nanostructures Using Anodic and Cathodic Reactions

Abstract

A two-step electrochemical process using anodic and cathodic reactions was developed to form size-controlled nanostructures on InP͑001͒ substrates. After anodic formation of a nanopore array, the cathodic decomposition process was applied to reduce the thickness of InP nanowalls. The etching rate of the nanowalls was extremely small and strongly dependent on the cathodic bias and crystal orientations of the wall surface. Wall thickness could be controlled in the range of 10-30 nm by changing the cathodic bias and processing time. © 2007 The Electrochemical Society. ͓DOI: 10.1149/1.2713662͔ All rights reserved.Manuscript submitted November 9, 2006; revised manuscript received January 10, 2007. Available electronically March 13, 2007. High-density formation of semiconductor nanostructures has recently been intensely researched for applications such as photonic crystals, quantum and optoelectronic devices, and chemical and biochemical sensors. Mainstream approaches to forming semiconductor nanostructures have used conventional methods such as lithography, dry etching, or crystal growth processes. For example, reactive ionbeam etching ͑RIBE͒, molecular beam epitaxy ͑MBE͒, and metallorganic vapor phase epitaxy ͑MOVPE͒ are common techniques for this purpose in the semiconductor community. One possible alternative approach is to apply the electrochemical process to semiconductors. With this process, a wide variety of semiconductor nanostructures can be obtained by modifying the surface using electrochemical anodic and cathodic reactions. The electrochemical process seems to be extremely promising for creating semiconductor nanostructures due to its unique features such as being a lowtemperature process, causing low processing damage, and having a simple process and a low cost.The most well-known application of the electrochemical process is for forming a porous Si structure using the anodic reaction in an HF-based electrolyte.1-3 This has given a visible light-emitting property to Si by modifying the surface. Canham 3 reported that the photoluminescence ͑PL͒ peak obtained from porous Si showed a significant blue shift with reference to the bandgap energy of a bulk Si, showing evidence of quantum confinement in porous structures. Several groups later reported on porous structures made of III-V semiconductor materials such as GaAs, 4,5 GaP, 6,7 InP, [8][9][10]12 Up to the present, various crystal orientations and electrochemical conditions have been investigated on III-V materials to reveal structural properties and their tunability. We have recently succeeded in the anodic formation of arrays of straight nanopores on n-InP͑001͒ substrates. [13][14][15] The straightness of pores in the depth direction has been dramatically improved using an HCl-based electrolyte containing a small amount of HNO 3 , resulting in the formation of a high-density array of InP nanowalls with a high aspect ratio. These kinds of unique nanostructures have not been obtainable by other methods.In this article, we report size-controlled InP nan...

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

“…It is important to remember that the pore shape was a square defined by four equivalent ͕100͖ planes, which is similar to the shape of the porous structures after the cathodic decomposition process. 17 This similarity is due to the strong dependence of the etching rate on crystal orientation, where the ͕100͖ planes preferentially appeared on the wall surface due to their slow etching rate. The lateral thickness of the InP nanowalls was less than 20 nm near the surface, which is thinner than the initial value of the template porous sample.…”

“…[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.…”

“…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.…”

Correlation between Structural and Photoelectrochemical Properties of GaN Porous Nanostructures Formed by Photo-Assisted Electrochemical Etching

“…17 We have recently reported that InP porous nanostructures showed low photoreflectance and high photoabsorption, 18,19 which are very promising features for porous nanostructures used in the photoelectric conversion devices such as photodetectors and solar cells. Besides, the electrochemical process is applicable to various semiconductors, [20][21][22][23][24] even chemically stable materials such as GaN, [25][26][27][28][29] without causing processing damage. The electrochemical conditions including applied bias and electrolyte solutions have been investigated with regard to the formation of GaN porous nanostructures, but most of the previous studies targeted structural properties and only a few reported on the correlation between the conditions and the resultant optical properties.…”

Electrochemical Functionalization of InP Porous Nanostructures with a GOD Membrane for Amperometric Glucose Sensors

“…26 Here, pore diameter and wall thickness can be controlled by adjusting the electrochemical anodic and cathodic conditions. 27 After that, the porous surface was photoelectrochemically etched in the same electrolyte under illumination to remove the disordered irregular layer formed at the initial stage of pore formation.…”