Vladimir V. Romanov

Superconductivity in silicon nanostructures

Superconducting properties of silicon sandwich nanostructures on the n-Si (100) surface, which represent the ultra-narrow p-type silicon quantum wells confined by heavily boron-doped δ barriers, manifest themselves in the measurements of the temperature and field dependences of resistivity, thermopower, heat capacity, and static magnetic susceptibility. The cyclotron-resonance, scanning-tunneling-microscopy, and ESR data identify the presence of the single trigonal negative-U dipole boron centers in nanostructured δ barriers B+-,B−, which are formed due to the reconstruction of shallow boron acceptors, 2B0 ⇒ B+ + B−. The obtained results indicate that these negative-U centers are responsible for the transport of small-radius hole bipolarons, which is likely the basis of the mechanism of high-temperature superconductivity with TC = 145 K. The superconductor-gap value of 0.044 eV determined from the measurements of the critical temperature using the above techniques is almost identical to the data on the tunneling spectroscopy and direct record of tunneling I–V characteristics. The quantization of the superconductive characteristics for silicon sandwich nanostructures manifests itself in the temperature and field dependences of the heat capacity and static magnetic susceptibility, which show the oscillations of the second critical field and critical temperature arising due to the supercurrent quantization.

Superconductor Properties for Silicon Nanostructures

Semiconductor silicon is well known to be the principal material for micro and nanoelectronics. Specifically, the developments of the silicon planar technology are a basis of the metal-oxygen-silicon (MOS) structures and silicon-germanium (Si-Ge) heterojunctions that are successfully used as elements of modern processors (Macilwain, 2005). Just the same goals of future high frequency processors especially to resolve the problem of quantum computing are proposed to need the application of the superconductor nanostructures that represent the Josephson junction series (Nakamura & Tsai, 2000). Therefore the manufacture of superconductor device structures within frameworks of the silicon planar technology seems to give rise to new generations in nanoelectronics. Furthermore, one of the best candidate on the role of the superconductor silicon nanostructure appears to be the high mobility silicon quantum wells (Si-QW) of the p-type confined by the δ-barriers heavily doped with boron on the n-type Si (100) surface which exhibit the properties of high temperature superconductors (Bagraev et al., 2006a). Besides, the heavily boron doping has been found to assist also the superconductivity in diamond (Ekimov et al., 2004). Here we present the findings of the electrical resistance, thermo-emf, specific heat and magnetic susceptibility measurements that are actually evidence of the superconductor properties for the δ-barriers heavily doped with boron which appear to result from the transfer of the small hole bipolarons through the negative-U dipole centres of boron at the Si-QW – δbarrier interfaces. These ‘sandwich’ structures, S-Si-QW-S, are shown to be type II high temperature superconductors (HTS) with characteristics dependent on the sheet density of holes in the p-type Si-QW. The transfer of the small hole bipolarons appears to be revealed also in the studies of the proximity effect that is caused by the interplay of the multiple Andreev reflection (MAR) processes and the quantization of the supercurrent.

Light emission from erbium-doped nanostructures embedded in silicon microcavities

Abstract We present the findings of high-efficient Er 3+ -related 4 I 13/2 ↔ 4 I 15/2 absorption and emission from self-assembled quantum wells (SQW) embedded in silicon microcavities. The microcavities are prepared by the short-time diffusion of boron into the Si (1 0 0) wafer doped with erbium. The intraband electron transitions accompanied by tunneling through strongly coupled SQW series are observed to excite the 4 I 13/2 ↔ 4 I 15/2 Er 3+ -intracenter emission, 1.54 μm , that is enhanced by strong sp–f mixing in the range of the Rabi splitting revealed by the transmission spectra.

Electrically-detected ESR in silicon nanostructures inserted in microcavities

We present the first findings of the new electrically-detected electron spin resonance technique (EDESR), which reveal the point defects in the ultra-narrow silicon quantum wells (Si-QW) confined by the superconductor delta-barriers. This technique allows the ESR identification without application of an external cavity, as well as a high frequency source and recorder, and with measuring the only response of the magnetoresistance, with internal GHz Josephson emission within frameworks of the normal-mode coupling (NMC) caused by the microcavities embedded in the Si-QW plane.

Electrically-detected magnetic resonance in semiconductor nanostructures inserted in microcavities

We present the first findings of the new electrically-detected electron spin resonance technique (EDESR), which reveal the point defects in the ultra-narrow silicon quantum wells (Si-QW) confined by the superconductor δ-barriers. This technique allows the ESR identification without application of an external cavity, as well as a high frequency source and recorder, and with measuring the only response of the magnetoresistance caused by the microcavities embedded in the Si-QW plane.