Scanning tunneling spectroscopic monitoring of surface states role on water passivation of InGaAs uncapped quantum dots

Abstract

A detailed local analysis of the impact of water coverage on the density of surface states in In 0.5 Ga 0.5 As surface nanostructures is reported by spectroscopy monitoring the surface conductivity at the nanometer-scale. A correlation between the changes of the surface conductivity and the variation of the density of surface states under different environmental conditions is found in terms of I-V characteristics and scanning tunneling spectroscopy. From dry to humid conditions the surface conductivity of a threedimensional In 0.5 Ga 0.5 As uncapped nanostructured surface increases monotonically with the reduction of the density of available surface states. In contrast, neither the electrical properties nor the density of electrically active surface states of a surface quantum well exhibit any significant dependence on the external moist conditions. The adsorption of water molecules onto the surface passivates the surface states leading to an improvement in the electron transport. These results clearly reveal that the density of surface states depends on the dimensionality of a nanostructured surface and demonstrate the important role of these states for nanoengineering sensing devices.