In recent years the attachment of biomolecules to semiconductor surfaces has been identified as an essential step for the fabrication of devices in molecular electronics, biosensors, and other diagnostic materials. In the fabrication of biosensors a brush like structure of the probe is required to increase the efficiency of hybridization of the target molecule. We have successfully attached ss-DNA oilgonuleotides to As-terminated GaAs (001) with a covalent bonding between S and As. Some attachment through N-As and O-As also takes place. To enhance the brush–like structure, 6-mercapto-1-hexanol (MCH) was added to displace the N-As and O-As bonding by the stronger/preferred S-As bonding. To minimize the pi-pi stacking that occurs among the ss-DNA oligos during the attachment, the following two procedures were carried out: (1) increasing the ionic strength of the solution to establish charge screening, and (2) sonication after attachment. Grazing incidence x-ray scattering of the attached DNA shows a preferred orientation of the DNA oligos along the trenches in the [110] direction of the GaAs. Analysis by AFM shows an enhancement of the brush-like structure with addition of NaCl, which increases the ionic strength of the solution that leads to the decrease of the pi-pi stacking.

This work is supported by the Department of Energy-Innovations under the Nuclear Infrastructure and Education (INIE) program.