Nano-orbitronics in silicon

Shallow donor impurities in silicon, once frozen out at low temperature, share many properties in common with free hydrogen atoms [1]. They have long been the subject of spectroscopic investigation, but it is only very recently [2,3] that it has been possible to investigate the time-domain dynamics of orbital excitations such as the 1 s to 2p, due to the difficulty of obtaining short, intense pulses in the relevant wavelength range. These new techniques make shallow donors (and also acceptors [4]) attractive for studying atomic physics effects, and for applications in quantum information. We have measured the population dynamics of electrons orbiting around phosphorus impurities in commercially-available silicon, and shown that the lattice relaxation lifetime is about 200 ps, only 1 order of magnitude shorter than the radiative lifetime of free hydrogen.