Electrochemical and optical characterizations of anodic porous n-InP(1 0 0) layers

In this paper, electrochemical and optical characterizations of anodic porous n-InP(1 0 0) are reported. The direct relation between the observed pore morphology and the physical properties is demonstrated using electrochemical methods such as cyclic voltammetry and impedance spectroscopy as well as optical techniques like photocurrent spectroscopy and photoluminescence measurements. An enhancement of the interfacial capacitance, proportional to the anodic charge, is revealed by voltammetry and Mott-Schottky analysis. It is related to the drastic increase of the area of the porous electrode. However, when the porous samples are sufficiently reverse-biased, the capacitance enlargement disappears because the nanosized pore walls are fully depleted and the electroactive area recovers its initial value. Photocurrent spectroscopy and photoluminescence measurements show the porous film behaves like an absorbent layer. This effect is also ascribed to the specific geometry of the space charge layer within the pore walls. A model based on the absorption coefficient and the effective optical path length is thus used to describe the phenomenon. However the model is not sufficient to depict the phenomenon and the charge recombination in the additional surface states created during the pore formation and the long transit time of electrons in the porous matrix are also significant. Additional effects such as the initial enhancement of the photocurrent response and the redshift of the absorption edge of the photocurrent spectra are observed. Inversely, no shift of the photoluminescence peak is detected. However an exponential quenching of the photoluminescence is also attributed to an absorbent behavior of the porous layer.