weitere Autoren: PD. Dr. Thomas Friedrich; Univ. - Prof. Dr. rer. nat. habil. Ambacher, Oliver

We report on the growth of silicon nanowires on photostructurable glass by low-pressure chemical vapour deposition. Thereby, no additional catalyst was needed to stimulate the growth process. Instead, a self-organized crystallization process leads to the formation of metallic clusters and seed crystals within the glass, which are supposed to initialize the nanowire growth. The nanowires were contacted by direct deposition of Pt using a focussed ion beam system and characterized electrically.

The resonant frequencies and quality factors of MEMS and NEMS depend critically on the layer quality and the residual stress in the SiC/Si heterostructure. It is demonstrated, that FTIR-ellipsometry is a suitable technique for monitoring the inhomogeneous residual stress inside SiC/Si heterostructures containing thin layers and their variation with during processing.

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.

In this work we have investigated the impact of typical device processing steps on the surface properties (roughness, chemical composition, contact angle to water) of group III-nitride based chemical sensors with emphasis on the electrical performance of the sensor and the biocompatibility. Basic sensing device is an AlGaN/GaN high electron mobility transistor. The widely distributed mammalian cell cultures HEK 293FT and CHO-K1 served as biological model systems. The processing of the devices had only little influence on the cell growth onto the sensor. In all cases it was superior to silicon surfaces. Fluorine dry etching smoothes the surface and forms an oxide, which improves 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. For all other treatments the contact angle recaptures a value of about 50 +/- 5 degrees after exposure to air or water droplets for some hours due to the contamination by hydrocarbons.

A pulsed mode magnetomotive operation of micro- and nanoelectromechanical devices in air is demonstrated, where viscous damping determines the quality factor of the device. An enhancement of the quality factor by increasing the resonant frequency using strained resonator structures is proposed. Internal strain is the result of the thermal mismatch between heteroepitaxial SiC or AlN layers and the silicon substrates. Comparing unstrained and strained resonators, an increase of the quality factor by one order of magnitude from about 30 to 300 was achieved. This increase will improve the sensing performance of such resonant structures for an operation in ambient environment.

We propose the development of a basic module for a novel nanowire-based nanoelectromechanical device, which will require the mechanical coupling of nanowires to an AlGaN/GaN heterostructure containing a polarization-induced 2D electron gas. The deflection of freestanding nanowires in a streaming liquid causes an additional strain in the AlGaN barrier which leads to a change in the resistance of the 2D electron gas. The basic structure, underlying theoretical considerations and first steps towards the realization of this new sensor concept are presented.