AlGaN/GaN biosensor—effect of device processing steps on the surface properties and biocompatibility

The impact of typical device processing steps (KOH, HCl, HF wet chemical etching, SF6 and Cl plasma etching) on the surface properties (roughness, chemical composition, contact angle to water) of group III-nitride based chemical sensors is investigated with emphasis on the electrical performance of the sensor and the biocompatibility. An AlGaN/GaN high electron mobility transistor serves as basic sensing device. For our studies, the widely distributed mammalian cell cultures HEK 293FT and CHO-K1 are used as biological model systems. The processing of the devices has only little influence on the cell growth onto the sensor, which is in all cases superior to that on silicon surfaces. Fluorine dry etching leads to oxidation and smoothing of the surface, thus, improving the electrical properties of the AlGaN/GaN sensor. In contrast, autoclave treatment enhances the carbon contamination with negative impact on the sensor properties and increased the contact angle to water, which can be used as indicator for the state of the sensor surface. For all other treatments the contact angle recaptures a stable value of about 50 ± 5° after exposure to air or water droplets for some hours due to contamination by hydrocarbons.