Optical Detection and Ionization of Donors in Specific Electronic and Nuclear Spin States

Abstract

We resolve the remarkably sharp bound exciton transitions of highly enriched 28Si using a single-frequency laser and photoluminescence excitation spectroscopy, as well as photocurrent spectroscopy. Well-resolved doublets in the spectrum of the 31P donor reflect the hyperfine coupling of the electronic and nuclear donor spins. The optical detection of the nuclear spin state, and selective pumping and ionization of donors in specific electronic and nuclear spin states, suggests a number of new possibilities which could be useful for the realization of silicon-based quantum computers.

Silicon as a model ion trap: Time domain measurements of donor Rydberg states

“…The Bohr model is equally applicable to donor impurity atoms in semiconductor physics, where the conduction band corresponds to the vacuum, and the loosely bound electron orbiting a singly charged core has a hydrogen-like spectrum according to the usual Bohr-Sommerfeld formula, shifted to the far-infrared because of the small effective mass and high dielectric constant. As with atoms in traps the ground states are tightly confined and well isolated from the environment, giving rise to extraordinarily sharp transitions (3)(4)(5) and very long spin coherence times (6,7), measured with magnetic resonance experiments. There are several proposals for quantum information processing based on the spin of silicon donors (8)(9)(10)(11)(12)(13) and such impurities can now be placed singly with atomic precision (14).…”

“…For a real material, however, determination of relaxation times from the frequency domain linewidth is notoriously difficult because the observed shape of the absorption line is generally given by a convolution of the homogenous (or natural) linewidth with the instrument response and a variety of inhomogenous broadening mechanisms. The latter include random strain fields induced by impurities and/or dislocations (16,17), and other fluctuations in the donor environment caused by chemical impurities and different isotopes in the natural composition of Si with differing nuclear moment (3)(4)(5). Time-domain methods such as ours (18,19) can directly measure the relaxation without any convolution, but require a short-pulse laser, in our case, a far-infrared free-electron laser.…”

Impurity absorption spectroscopy of the deep double donor sulfur in isotopically enriched silicon

“…This material had previously proven to be of excellent quality [24,25], both in terms of isotopic enrichment as well as chemical purity. It has to be noted that the chemical purity of isotopically enriched silicon at the present stage does not yet meet that of UHP natural silicon.…”

“…The 30Si:nats sample was kept in the furnace for 24 hours at 1100 0 e. Here we see that it is possible to obtain a scan of the entire spectrum over all wavenumbers but on the other hand equation (3.5) also shows a limitation of the Fourier transform spectrometer. A real interferometer will always have a limited retardation 5 and as we shall see this results in a finite resolution.…”

“…The UHP Si sample was used to observe transitions of neutral centres like Sa and sg while the Si:B sample is better suited to observe ionized S+ impurity centres due to the higher B acceptor concentration. The ampule was kept in the furnace for about 24 hours at 1100 0 e.…”