Process of Formation of Porous Layers in n-InP

Abstract

The anodic formation of porosity in semiconductors has received considerable attention, due to the fundamental insight it offers into semiconductor etching properties and its wide range of possible applications [1]. Although a number of models have been proposed to explain the formation of porosity in semiconductors [2-5], none as yet can explain the complete range of structures which have been formed in different semiconductor-electrolyte systems. The anodic etching of n-type semiconductors in the dark is limited by hole supply at the semiconductor surface. It is generally accepted that this limited hole supply is what causes the initiation and propagation of porous etching, with hole supply being enhanced (and hence, porous etching initiated) at defect sites at the surface [6]. The newly formed pore tips then act as sites for the continuous preferential supply of holes [5]. However, the variation in feature size, as well as the morphology observed, as experimental conditions are varied cannot be so readily explained. We have developed a mechanism [7], based on our results for pore formation in n-InP in KOH, in which the variations in pore morphology are due to the competition in kinetics between hole supply, carrier diffusion at the semiconductor surface and the electrochemical reaction. The mechanism is represented schematically in Fig. 1. The mechanism can be used to explain the characteristic width of the pore structures, and their directional preference. In this presentation we will review our recent results and show that they are in support of the mechanism [8-10]. We will also present the results from numerical modelling of pore formation in InP based on the aforementioned pore growth mechanism.