Nano-island fabrication by electron beam lithography and selective oxidation of Al-rich AlGaAs layers for single electron device application

A nanometer-scale island embedded between two tunnel junctions constitutes the elementary cell of single electron devices (SED), such as single electron transistors (SET) and memories. In this work we report on a new method for the fabrication of a nanometer-scale semiconductor island through AlGaAs/GaAs epitaxial growth, electron beam lithography and selective oxidation of Al-rich AlGaAs layers. We have used a combination of high-resolution electron beam lithography and selective oxidation of Al-rich AlGaAs layers in order to fabricate a non-oxidized semiconductor island smaller than the electron beam lithography (EBL) defined size. The pattern was transferred down to the bottom AlAs layer and a selective oxidation of the Al-rich layers was performed in water vapor at a temperature of 300 °C, which led to the formation of the aluminum oxide. The higher oxidation rate of the AlAs compared to the Al0.8Ga0.2As layer, together with the strain accumulation in the Al0.8Ga0.2As, caused the formation of nanoscale semiconductor islands embedded in an aluminum oxide shell. After the oxidation and cleavage of the sample, selective wet etching has been performed in order to evidence the unoxidized region through an SEM inspection.