Competitive adsorption of air constituents as observed on InGaN/GaN nano-optical probes

The photoluminescence properties of InGaN/GaN nanowire arrays were used to probe the adsorption of H2O, O2, NO2 and O3 on III-nitride surfaces. Upon adsorption these gases either enhance (H2O) or quench (O2, NO2, O3) the photoluminescence intensity which allows the related adsorption processes to be evaluated. An analysis of the experimental data in terms of the Langmuir Adsorption and Recombination model reveals that - at room temperature - the Langmuir energy of adsorption Eads increases in the order H2O, O2, NO2, and O3 and that for each gas species Eads increases linearly with increasing surface temperature. We show that this behaviour can be explained by a competition of these air constituents for the same kind of Ga(In) adsorption sites. In contrast, exploratory experiments with H2 and simple hydrocarbons reveal that these reducing species neither quench nor enhance the native photoluminescence response, which indicates that these do not compete for the same adsorption sites as the background air constituents.