Photocurrent enhancement in hybrid nanocrystal quantum-dot p-i-n photovoltaic devices.

We fabricate a hybrid nanocrystal quantum-dot patterned p-i-n structure that utilizes nonradiative energy transfer from highly absorbing colloidal nanocrystal quantum dots to a patterned semiconductor slab to demonstrate a sixfold increase of the photocurrent conversion efficiency compared to the bare p-i-n semiconductor device.

High temperature gate control of quantum well spin memory.

Time-resolved optical measurements in (110)-oriented GaAs/AlGaAs quantum wells show a tenfold increase of the spin-relaxation rate as a function of applied electric field from 20 to 80 kV cm(-1) at 170 K and indicate a similar variation at 300 K, in agreement with calculations based on the Rashba effect. Spin relaxation is almost field independent below 20 kV cm(-1) reflecting quantum well interface asymmetry. The results indicate the achievability of a voltage-gateable spin-memory time longer than 3 ns simultaneously with a high electron mobility.

Precession and motional slowing of spin evolution in a high mobility two-dimensional electron gas.

Optical spin-dynamic measurements in a high-mobility n-doped GaAs/AlGaAs quantum well show oscillatory evolution at 1.8 K consistent with a quasi-collision-free D'yakonov-Perel'-Kachorovskii regime. Above 5 K evolution becomes exponential as expected for collision-dominated spin dynamics. Momentum scattering times extracted from Hall mobility and Monte Carlo simulation of spin polarization agree at 1.8 K but diverge at higher temperatures, indicating the importance of electron-electron scattering and an intrinsic upper limit for the spin-relaxation rate.

Measurement of the hyperfine structure of Pr(3:):YAG by quantum-beat free-induction decay, hole burning, and optically detected nuclear quadrupole resonance.

The hyperfine splitting of the ground state and the lowest electronic component of the (1)D(2) excited state have been measured for Pr(3+) in YAG. We show that a particularly simple and powerful technique is the production of sublevel coherence by short-pulse (impact) excitation, which is detected by coherent forward scattering of a weak probe beam and Fourier transformation of the resulting quantum-beat signal. This yielded excited-state splittings of 6.49 and 8.29 MHz. The ground state shows large pseudoquadrupole splittings of 33.4 and 41.6 MHz, which were obtained by optically detected nuclear quadrupole resonance.