No abstract

A strain-balance multiquantum well (MQW) approach to enhance the GaAs solar cell efficiency is reported. Using a p-i-n diode structure, the strain-balanced GaAsP/InGaAs MQW is grown on a GaAs substrate and equals a good GaAs cell in terms of power conversion efficiency. The cell design is presented together with measurements of the forward bias dark current density, quantum efficiency, and 3000 K light-IV response. Cell efficiencies under standard air mass (AM) 1.5 and AM 0 illumination are projected from experimental data and the suitability of this cell for enhancing GaInP/GaAs tandem cell efficiencies is discussed.

We have observed a Fermi-edge singularity in the tunneling current between a two-dimensional electron gas (2DEG) and a zero-dimensional localized state. A sharp peak in the tunnel current is observed when the energy of the localized state matches the Fermi energy of the 2DEG. The peak gro~s and becomes sharper as the temperature is decreased to our lowest temperature of 70 mK. We attribute the singularity to the Coulomb interaction between the tunneling electron on the localized site and the Fermi sea.

Resistively detected nuclear magnetic resonance measurements have been performed on a high mobility heterostructure in the quantum Hall regime. At millikelvin temperatures the nuclear resonances are observed in the vicinity of various integer and fractional filling factors without previous dynamic nuclear polarization. Near nu = 1, the observed large enhancement of the resonance amplitude accompanied by a reduction of T1 strongly suggests a greatly increased coupling between the electronic and nuclear spin systems. This is consistent with the proposed coupling of the nuclear spin system to the Goldstone mode of the Skyrme crystal.