High optical sensitivity to ambient conditions of uncapped InGaAs surface quantum dots

Abstract

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.

Photoexcited-induced sensitivity of InGaAs surface QDs to environment

“…Conversely, in a wet atmosphere the surface states are presumed to be linked to adsorbed water molecules. It has been previously addressed that water physisorption yields to an improvement of the electrical and optical characteristics, decreasing the SR and increasing the photoluminescence, respectively [10][11][12][13]. This has been attributed to a reduction of the density of active surface states after this physical process, in which the negative part of the water molecule dipole is attached to the positively charged surface states.…”

“…The strong correlation between external conditions and the optical properties of the InGaAs surface QD (SQD) has been addressed to rely on the coupling between surface and confined states [14][15][16][17]. PL intensity quenches under vacuum and decreases in dry environments, whereas it is maintained under water-vapor-containing atmospheres [11]. Features of molecules in the surroundings, such as molecular weight, polar character and size among others, have been suggested to be responsible for similar effects [18,19].…”

“…Materials such as porous Si [3], ZnO nanostructures [4], colloidal II-VI quantum dots (QDs), graphene [5], carbon QDs [6] and III-V semiconductors [7][8][9] have been proposed as candidates for the development of environmental sensing devices. In particular, surface compound nanostructures based on the high mature arsenide technology (III-As) have recently reported a high sensitivity to external conditions [10][11][12][13]. The strong correlation between external conditions and the optical properties of the InGaAs surface QD (SQD) has been addressed to rely on the coupling between surface and confined states [14][15][16][17].…”

Chemical sensitivity of InP/In0.48Ga0.52P surface quantum dots studied by time-resolved photoluminescence spectroscopy

“…A strong sensitivity to the surface environment has been reported for SQDs made of InAs [13], InGaAs [7] and InP [8]. These QDs are not suitable to be used in solution, and thus cannot be exploited for application like in vivo imaging and diagnostics.…”

“…Recently, a new approach has been introduced which is based on Surface QDs (SQDs) grown by epitaxy on solid substrates [7,8]. Usually, epitaxial quantum dots require a capping layer of a wider band gap semiconductor providing charge carriers confinement and non-radiative surface state passivation.…”