Solar Energy Materials and Solar Cells 25 (1992) 179-189 North-Holland Solar Energy Materials and Solar Cells Photoelectrochemical etching of n-InP producing antireflecting structures for solar cells D. Soltz a, L. Cescato ~ and F. Decker b,l Laborat6rio de Optica DFESCM, IFGW C.P. 6165, UNICAMP, Campinas 13081, SP, Brazil b Laborat6rio de Electroquimica DFA, IFGW C.P. 6165, UNICAMP, Campinas 13081, SP, Brazil Photoelectrochemical (PEC) etching of n-lnP is studied as a method to engrave relief microstructures. Experiments of PEC etching were performed with holographic exposures (A = 0.4579 Ixm) and homogeneous white light on n-InP. The triangular profile characteristic of holographic patterns recorded parallel to the (011) direction appeared even when the sample was etched using homogenous white light. In this case deep random microstructures were obtained which present interesting antireflection properties that may be useful in solar cell applications. I. Introduction Relief grating microstructures of a high spatial frequency and aspect ratio (depth/width) have good antireflecting properties. These structures can function over a larger range of wavelengths and incident angles than the antireflecting coatings normally used for solar cells. Deep microstructures of a period smaller than the wavelength of the light create a gradient for the index of refraction, thereby reducing reflection [1,2]. The size and depth of microstructures formed on InP using traditional pho- tolithographic techniques is limited by the resolution of the resist itself, and by undercutting of the mask due to a high lateral etch rate [3]. Photoelectrochemical (PEC) etching can be used to engrave microstructures onto the surface of InP substrates without the use of masking [4,5]. Electrochemical (EC) and PEC etching of semiconductors are generally pro- cesses of anodic dissolution; the constituents of the semiconductor are oxidized by holes, and enter the solution as cations. The corrosion reaction can take place in the dark for p-type materials (where the holes are the majority carriers), but only occurs in the presence of light for n-type materials (where electrons are the majority carriers). Fig. 1 shows the PEC corrosion reaction for n-InP, where the junction of the semiconductor with the electrolyte follows the model of Gerischer [6,7]. t Department of Chemistry, Universit?t La Sapienza, Piazzale Aldo Moro 5, 00185 Rome, Italy. 0927-0248/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved