Changing photoluminescence intensity from GaAs/Al0.3Ga0.7As heterostructures upon chemisorption of SO2

Abstract

Chemisorption of SO2 gas molecules onto photowashed GaAs surfaces results in a change in the density of charge at the surface, giving rise to a measurable change in the charge distribution within the semiconductor. We consider the development of a novel semiconductor chemical sensor based on this phenomenon. The intensity of photoluminescence (PL) from metalorganic vapor phase epitaxy grown GaAs/Al0.3Ga0.7As structures at 300 K is used to detect this change in charge distribution. The doping densities and layer thicknesses within these heterostructures are shown to have a profound influence on the relative magnitude of PL intensity and its sensitivity to changes in the density of surface charge brought about by chemisorption of SO2. New analytical and finite element method (FEM) numerical models are derived to quantitatively predict the effect of changing surface charge on the PL intensity from finite thickness heterostructure layers. The PL response from these heterostructures is shown to follow the trends predicted by these models and suggests that the adsorption of SO2 from a 0.6 mol % mixture of SO2 in N2 results in a reduction in the negative surface charge density by 9×109 to 2×1010 cm−2. Simultaneous changes in surface recombination rates due to adsorption are shown (using the FEM model) to have no effect on the PL intensity from the structures studied here. The results are applied to the improvement of signal characteristics from a potential chemical sensor device.