Pore Etching in Compound Semiconductors for the Production of Photonic Crystals

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Pore Etching in Compound Semiconductors for the Production of Photonic Crystals Helmut Foell1, Sergiu Langa1,2, Juergen Carstensen1, Marc Christophersen1, Ivan Tiginyanu2, Karin Dichtel3 1

Faculty of Engineering, University of Kiel, Germany Technical University of Moldova, Moldova 3 Physics Department, University of Kiel, Germany 2

ABSTRACT Ordered arrays of pores in Si provided the first (two dimensional) photonic crystals with bandgaps in the µm region. The paper explores the potential of pore etching for two- and threedimensional photonic crystals in GaAs, InP, and GaP. A striking feature of pore etching in III-V semiconductors is the strong tendency to self-organization and pattern formation. As an example, self-organized well-defined pore lattices (a = 100 nm – 1 µm) can be made in InP. All materials show self organized diameter oscillations, often synchronized over large distances between pores. Extremely strong diameter oscillations are observed in GaAs. Pores in all materials tend to grow in directions, but can be induced to grow in the direction of current flow, too. These features can be used to produce two- and three dimensional photonic crystals. The latter goal might be achieved by switching periodically between different pore morphologies with depth, or by modulating the diameter with depth - always helped by the tendency to self organization. Self organization, however, will not lead to perfect crystal structures; lithographically defined nucleation is needed and has been tried. First results show that there are pronounced differences to what is known from Si. While the production of externally defined photonic crystals in the sub µm region appears to be feasible, the strong tendency to self organization must be taken into account by matching internal time and length scales to the desired external ones. INTRODUCTION The first two-dimensional photonic crystal with a band gap in the µm region and with defined defects was made from porous Si [1,2]. Meanwhile porous Al2O3 is also considered an attractive material for photonic crystal purposes [3]. In both cases the pores were etched electrochemically. The aim of the present paper is to explore the potential of electrochemical pore etching for the production of photonic crystals, in particular with respect to III-V compound semiconductors. The possibilities for two- and three-dimensional pore crystals will be discussed separately, including some relevant aspects of Si pore crystals. It is important to note in this context that pore etching in Si is far from being fully understood, and even less is known about pore etching in other semiconductors. While there are plenty of experimentally observed phenomena, some of which appear to hold promise for photonic crystals, the full potential of pore etching can only be utilized, if the basic processes responsible for pore formation are understood as will be shown below. While Si is an ideal material for making pore crystals from the viewpoint of cost, size and perfection, its major disadvantages are: i) large ab