Electrochemical formation of porous superlattices on n-type (1 0 0) InP Hiroaki Tsuchiya a , Michael Hueppe b , Thierry Djenizian b , Patrik Schmuki b, * a Department of Materials Science and Processing, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan b Department of Materials Science, University of Erlangen-Nuremberg, Martensstrasse 7, D-91058 Erlangen, Germany Received 28 April 2003; accepted for publication 12 October 2003 Abstract The present work deals with the electrochemical formation of superlattice structures on n-type (1 0 0) InP in HCl solutions. The superlattices consist of a stack of two layers with alternating high and low porosity on n-type material obtained by changing the anodizing current or the potential periodically in HCl solutions. The superlattice structures were characterized by scanning electron microscopy. The pore morphology and structure depend strongly on the electrochemical conditions. For anodization with low currents (e.g., 1 or 10 mA) or at low potentials (e.g., 1.5 V Ag=AgCl ), a porous layer with a facet-like structure was formed. For higher currents or potentials, such as 50 or 100 mA or 3 V Ag=AgCl , respectively, a tree-like structure with random and/or tangled branches was observed. Finally, samples anodized at 5 V Ag=AgCl , show a porous layer with a regular array of straight pores. The morphology and structure of the stacks of the porous layers can be controlled in the nanometer range, depending on the electrochemical conditions. Ó 2003 Elsevier B.V. All rights reserved. Keywords: Superlattices; Electrochemical methods; Scanning electron microscopy (SEM); Surface structure, morphology, roughness, and topography; Indium phosphide 1. Introduction Since the discovery of efficient room tempera- ture visible photoluminescence of porous silicon formed by partial electrochemical dissolution [1], porous silicon has attracted much attention due to a variety of possibilities for optoelectronics and electronics device fabrication [2,3]. Compound semiconductors such as GaAs [4–9] and InP [10– 13] have also been investigated in view of the formation of porous layers and many different properties relative to the bulk materials have been revealed. Porous GaAs can be electrochemically formed in HCl and Cl ion containing solutions [6–9]. From these porous structures, visible photolumi- nescence in the green wavelength region of the spectrum can be observed [4,5]. For n-type (1 1 1) InP, porous structures were obtained by photoassisted etching in HCl electro- lytes [10,11]. These porous structures showed a weak blueshift in their photoluminescence spec- trum that was attributed to quantum confinement * Corresponding author. Tel.: +49-9131-852-7575; fax: +49- 9131-852-7582. E-mail address: schmuki@ww.uni-erlangen.de (P. Schmuki). 0039-6028/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.susc.2003.10.032 Surface Science 547 (2003) 268–274 www.elsevier.com/locate/susc