THE ETCHING KINETICS OF ILLUMINATED NORMAL-GAP IN NITRIC-ACID

The kinetics of etching of an illuminated n-type GaP in nitric acid has been studied. Speculation on the role of complex formation and the increase of the photo-assisted dissolution rate with time show the strong nitrite dependence on the characteristics of the observed electrode reaction. Comparison between results predicted from the established potential-pH diagram and the experimental results from inductively coupled plasma emission spectrometry data is given. Etching of an illuminated GaP electrode in HNO3 is believed to be an autocatalytic nitrous acid-catalyzed oxidation; the nitrite ion is also involved with the nucleophilic attack on the electron-deficient gallium element, along with the dissolution of phosphates or phosphorus oxides, to remove the electrode material. Based on the interfacial energy scheme of GaP/HNO3, the hindrance of the electron transfer between the GaP electrode and the NO3-/NO2 redox system is suggested to be responsible for kinetic inertness of GaP in a HNO3 etch, and is in agreement with this model.