The influence of the environment on the optical properties of self-assembled In0.5Ga0.5As surface quantum dots is studied as a function of different ambient conditions for sensing applications. Their room temperature photoluminescence (PL) quenches under vacuum and decreases strongly under dry O2 or N2 environments. Nevertheless, they have a strong signal at 1.55 μm in air or in a wet atmosphere. The presence of water molecules in the environment improves the PL intensity likely due to its polar character and therefore its easier adsorption by the surface dangling bonds, leading to a suppression of the non-radiative recombination centers.

The impact of the environment on the electrical properties of uncapped In0.5Ga0.5As nanostructures is studied as a function of different atmospheres for sensing applications. Electrical response from surface quantum dots (QD) shows a strong dependence on the atmosphere, in contrast to the response of 2D nanostructures. The sheet resistance drops by 99% from vacuum to air, and decreases more than one order of magnitude when relative humidity changes from 0 to 70%. The adsorption of water molecules onto the QD surface improves the conductivity likely by reducing the density of surface states acting as carrier traps, which enhances electron transport.

The photoluminescence (PL) of self-assembled In0.5Ga0.5As surface quantum dots is studied as a function of different species present in a controlled atmosphere. The presence of oxygen-containing molecules on the surface leads to a correlation of the PL intensity with the polarity and molecular mass of the species. Such molecules are more easily adsorbed, giving rise to a reduction of the number of nonradiative recombination centers and, therefore, to an enhanced PL of the dots. The strong dependence of the signal emission on the ambient conditions makes these nanostructures very promising for the development of sensing devices.

A detailed analysis of the impact of illumination on the electrical response of In 0.5 Ga 0.5 As surface nanostructures is carried out as a function of different relative humidity conditions. The importance of the surface-to-volume ratio for sensing applications is once more highlighted. From dark-to-photo conditions, the sheet resistance (SR) of a three-dimensional In 0.5 Ga 0.5 As nanostructure decays two orders of magnitude compared with that of a two-dimensional nanostructure. The electrical response is found to be vulnerable to the energy of the incident light and the external conditions. Illuminating with high energy light translates into an SR reduction of one order of magnitude under humid atmospheres, whereas it remains nearly unchanged under dry environments. Conversely, lighting with energy below the bulk energy bandgap, shows a negligible effect on the electrical properties regardless the local moisture. Both illumination and humidity are therefore needed for sensing. Photoexcited carriers can only contribute to conductivity if surface states are inactive due to water physisorption. The strong dependence of the electrical response on the environment makes these nanostructures very suitable for the development of highly sensitive and efficient sensing devices.

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