The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details.

Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details.

We study the effect on the density of states in mesoscopic ballistic billiards to which a superconducting lead is attached. The expression for the density of states is derived in the semiclassical S-matrix formalism shedding insight into the origin of the differences between the semiclassical theory and the corresponding result derived from random matrix models. Applications to a square billiard geometry and billiards with boundary roughness are discussed. The saturation of the quasiparticle excitation spectrum is related to the classical dynamics of the billiard. The influence of weak magnetic fields on the proximity effect in rough Andreev billiards is discussed and an analytical formula is derived. The semiclassical theory provides an interpretation for the suppression of the proximity effect in the presence of magnetic fields as a coherence effect of time reversed trajectories, similar to the weak localisation correction of the magneto-resistance in chaotic mesoscopic systems. The semiclassical theory is shown to be in good agreement with quantum mechanical calculations.

We demonstrate that the conductance of a field-effect transistor ͑FET͒ gated by a layer of nanometer-sized quantum dots is sensitive to the absorption of single photons. Rather than relying upon an avalanche process, as in conventional semiconductor single-photon detectors, the gain in this device derives from the fact that the conductivity of the FET channel is very sensitive to the photoexcited charge trapped in the dots. This phenomenon may allow a type of three-terminal single-photon detector to be developed based upon FET technology. © 2000 American Institute of Physics. ͓S0003-6951͑00͒01525-4͔Time-resolved single-photon detection is required for such diverse applications as medical diagnosis and imaging, chemical analysis, laser ranging, and materials characterization. 1 Photonic technology is also important for future applications in optical quantum cryptography and computing. Conventionally, single photons are detected by multiplication of a photogenerated carrier by an avalanche process, either in a vacuum photomultiplier tube, or, in the case of the semiconductor avalanche photodiode, a reversebiased junction ͑see, for example, Refs. 1-3͒. Here, we propose and demonstrate detection of single photons based upon an entirely different principle using a field-effect transistor ͑FET͒ containing quantum dots.Self-organizing growth techniques, based upon carefully controlled strained layer epitaxy, allow the formation of a high density of quantum dots with nanometer dimensions and relatively homogeneous size distribution. A particularly attractive aspect of this technique is that it can be used to produce quantum-dot layers within an epitaxially grown device structure. It has been shown that such a layer of selfassembled quantum dots can radically alter the transport properties of a nearby two-dimensional electron gas ͑2DEG͒. 4-6 Under illumination the quantum dots can trap photoexcited carriers, providing the possibility of using such dots as an optically addressed data storage medium. 7-11 Such structures have also been demonstrated as nonquantum detectors of midinfrared radiation through excitation of the bound-to-continuum intersubband photoconductivity. 12 It has been proposed 7 and demonstrated 8,10 that the inhomogeneous broadening of the quantum-dot optical transitions can be used to store more than one bit of information at each laser spot position, by tuning the laser wavelength to access dots with different transition energies. This requires a scheme to detect the presence of photoexcited charge in a single ͑or just a few͒ quantum dot. The results presented here demonstrate that by using a FET structure it is indeed possible to detect the presence of a single photoexcited carrier in a single quantum dot. Figure 1 shows a schematic of the device structure. It consists of a GaAs/Al 0.33 Ga 0.67 As modulation-doped FET containing a layer of InAs quantum dots separated from the 2DEG in the GaAs channel by a thin Al 0.33 Ga 0.67 As barrier. Since there are bound states of the quantum dots lying to lower ...