Optical active gallium arsenide probes for scanning probe microscopy

In order to produce microelectromechanical systems (MEMS) on base of gallium arsenide it is necessary to develop novel etching techniques. The conventional dip etching is not suitable to fabricate such systems reliably and with sufficiently small thickness variations. To overcome this problem we used a modified spray etching technique. A comparison between both methods is given. As a direct band gap semiconductor GaAs is used to fabricate light emitting probes with sub-wavelength apertures for scanning near-field optical microscopy (SNOM). The basic design consists of a GaAs cantilever with a vertical cavity surface emitting laser diode (VCSEL) integrated beneath the metallized tip. An aperture in the metallization layer at the apex is illuminated by the laser diode und thus serves as a miniaturized light source. This set-up simultaneously simplifies the cantilever deflection measurement. The laser beam emanating from the opposite side of the cantilever is detected with a position sensitive photo diode in accordance to the conventional light pointer method. We show a first probe with a VCSEL integrated in the very end of the cantilever. The short carrier life time in low temperature GaAs (LT-GaAs) enables the conversion of ultrashort optical into electrical pulses by means of a photoconductive gate. Based on this effect the voltage distribution of microwave devices can be investigated in the time domain by ultrafast scanning probe microscopy (USPM). For this purpose a photoconductive switch is integrated into an SFM probe to sample an electrical signal with picosecond time resolution. We report on the fabrication process of the modified SFM cantilever and first results.