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In this paper a silicon microphone which can be fabricated using standard semiconductor processes is presented. The acoustic-electrical transducer is based on the capacitance change of a movable 400 nm thin poly-silicon membrane with different diameters (800-1200 µm). A source follower was integrated to transform the impedance. The complete chip is 2 × 2 × 0.5 mm 3 in size. The sensitivity achieved is in the range of 0.4 to 3.2 mV Pa −1 .

We used focused ion beam insulation writing to fabricate quantum point contacts in the two-dimensional electron gas of an InGaAs/InAlAs heterostructure. The conductance as a function of voltage on an adjacent in-plane gate exhibited steps for temperatures up to 60 K. From the temperature and source-drain voltage and magnetic field dependence of the conductance steps, we estimated the one-dimensional subband spacing to be 15 meV.

We study the lateral spreading of implantation-induced damage and measure the position dependence of the cathodoluminescence intensity of GaAs/AlAs heterostructures patterned by a focused Ga+ ion beam. Two luminescence lines, one from a buried AlGaAs/GaAs quantum well and the other from a deeper lying AlAs/GaAs short period superlattice are detected. Implantation doses in the range 1012–1015 cm−2 are investigated. We find that the lateral spreading of implantation induced damage considerably exceeds the implanted region in the case of the quantum well (50 nm below the surface), but is well limited to the implanted region in the case of the superlattice (250 nm below the surface). Micro-Raman measurements allow us to locally probe the degree of crystallinity at a certain point of the sample.

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