Effective performances of chronoamperometry on the passivation process of n-InP in acidic liquid ammonia (-55 °C)

Abstract Chronoamperometry has proven to be a useful in-situ technique to investigate on the anodic passivation mechanism on n -InP semiconductors in acidic liquid ammonia. From our preliminary work, we assumed that the phosphazene film results from parallel electrochemical reactions: InP dissolution and ammonia oxidation. The main question posed here was based on the involvement of bromide (Br − ) from the conductive salt (NH 4 Br) in the anodic process. From chronoamperometry, the decrease in the current deviated from Cottrell behavior. No variation of the anodic charge and no shift of the anodic peak potential was found by using various ammonium halogenides (I - , Br - , Cl − ). Contrary to ammoniacate solvent, the reduction of Br 2 was never observed. These results suggested that the oxidation of Br − into Br 2 apparently could not occur during the anodic process. Thanks to chronoamperometry, the passivation rate constant was determined for the first time on InP in liquid ammonia. This constant (–k≈ 10 −2  s −1 ) was roughly similar to that described in the literature on Pt in aqueous alkaline solution during ammonia oxidation. As for on Pt, the deactivation of the surface could be interpreted as a partial electrochemical oxidation of ammonia on n -InP.