Abstract: Semiconductor structures and a method of forming semiconductor structures The avalanche breakdown characteristics, such as breakdown voltage and impact ionisation coefficient, of a semiconductor structure can be controlled by controlling the Brilluin-zone-averaged energy bandgap (<Ec>) of the material forming the structure. Consequently, the avalanche breakdown characteristics of a device may be tailored independently of the bandgap Eg. The Brillouin-zone-averaged energy bandgap (<Ec>) may be controlled by controlling the composition of the semiconductor used or by straining its lattice.

Abstract: Optically generated charge carriers in an optically responsive medium, such as an optical switch, which are produced in response to a first pulse of optical radiation (P1), are de-excited by directing a second pulse (P2) of optical radiation into the medium. The second pulse occurs while the excitation produced by the first pulse remains coherent, and the relative phase of the first and second pulses is selected so that the second pulse destructively interferes with the excitation produced by the first pulse. The apparatus may be used as an optical switch or as a photodetector.

Abstract: Nanometre scale particles (3) e.g. of Au are deposited on a Si substrate (2) with a SiO.sub.2 surface layer (1) provided with receptor sites (4) of a first electrical polarity by treatment with APTMS solution. The Au particles (3) have a surface charge (5) of a second opposite polarity e.g from surface adsorbed citrate ions, such that they are attracted to the surface sites on the substrate. The deposited Au particles are then released from the surface sites such that the particles move over the substrate and coalesce into a low dimensional aggregated structure. The aggregated structure may form at a surface irregularity on the surface of the substrate. The structure may be used in a quantum electronic device such as a single electron transistor.