A Magnetic Resonance Force Microscopy Quantum Computer with Tellurium Donors in Silicon

We propose a magnetic resonance force microscopy (MRFM)-based nuclear spin quantum computer using tellurium impurities in silicon. This approach to quantum computing combines the well-developed silicon technology with expected advances in MRFM.Comment: 9 pages, 1 figur

Insulator-to-metal transition in sulfur-doped silicon

We observe an insulator-to-metal (I-M) transition in crystalline silicon doped with sulfur to non- equilibrium concentrations using ion implantation followed by pulsed laser melting and rapid resolidification. This I-M transition is due to a dopant known to produce only deep levels at equilibrium concentrations. Temperature-dependent conductivity and Hall effect measurements for temperatures T > 1.7 K both indicate that a transition from insulating to metallic conduction occurs at a sulfur concentration between 1.8 and 4.3 x 10^20 cm-3. Conduction in insulating samples is consistent with variable range hopping with a Coulomb gap. The capacity for deep states to effect metallic conduction by delocalization is the only known route to bulk intermediate band photovoltaics in silicon.Comment: Submission formatting; 4 journal pages equivalen

Single Spin Measurement using Single Electron Transistors to Probe Two Electron Systems

We present a method for measuring single spins embedded in a solid by probing two electron systems with a single electron transistor (SET). Restrictions imposed by the Pauli Principle on allowed two electron states mean that the spin state of such systems has a profound impact on the orbital states (positions) of the electrons, a parameter which SET's are extremely well suited to measure. We focus on a particular system capable of being fabricated with current technology: a Te double donor in Si adjacent to a Si/SiO2 interface and lying directly beneath the SET island electrode, and we outline a measurement strategy capable of resolving single electron and nuclear spins in this system. We discuss the limitations of the measurement imposed by spin scattering arising from fluctuations emanating from the SET and from lattice phonons. We conclude that measurement of single spins, a necessary requirement for several proposed quantum computer architectures, is feasible in Si using this strategy.Comment: 22 Pages, 8 Figures; revised version contains updated references and small textual changes. Submitted to Phys. Rev.

Visible Light-Emitting Diodes - The Formative Years

A brief history of visible light-emitting diodes (LED's) is given, from the first experimental observations of H.J.Round in 1907 to the mid-1970's when red and green emitters were in extensive production. Early investigations were empirical. This was changed with the invention of the transistor in 1947 by the demonstration of minority carrier injection at a forward-biased junction, followed by recombination. In 1952 the discovery of the semiconducting behaviour of III-V compounds introduced a new range of materials. Gallium nitride seemed attractive for light emission and was investigated at Philips and RCA laboratories but at the time proved to be too difficult for practical use. Gallium phosphide emerged as the most promising material and groups to investigate it were set up at SERL in England, Philips Central Research Laboratories in Germany and Bell Telephone Laboratories in the USA. Zinc and oxygen doping gave red emission. At Philips, the emphasis was on efficiencies. At SERL the emphasis was on reproducibility for manufacturable devices and when the conditions for zinc and oxygen doping were strictly controlled the world's first practical visible LED's were produced at the end of 1961. At Bell Telephone Laboratories progress was initially slow but with the advent of liquid-phase epitaxial growth production of red emitters on the scale required became possible. The accidental discovery of nitrogen doping of gallium phosphide at Bell led to the production of good green emitters. Until the end of the 1970's, gallium phosphide red and green emitters dominated the LED market. Subsequent developments to the present day are sketched in outline