The bias voltage applied to a weakly coupled n-doped GaAs/AlAs superlattice increases the amplitude of the coherent hypersound oscillations generated by a femtosecond optical pulse. This bias-induced amplitude increase and experimentally observed spectral narrowing of the superlattice phonon mode with a frequency 441 GHz provides the evidence for hypersound amplification by stimulated emission ...

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We demonstrate a midinfrared source tunable from 6.7 to 12.7 μm via difference frequency generation (DFG) in orientation-patterned GaAs, with 1.3 mW average output power. The input pulses are generated via Raman self-frequency shift of a femtosecond Tm-doped-fiber laser system in a fluoride fiber. We numerically model the DFG process and show good agreement between simulations and experiments. ...

A GaN-based heterostructure barrier diode (HBD) similar to GaAs planar-doped barrier diodes is demonstrated. Instead of doping with impurities, the polarization-induced sheet charge at the III-nitride heterojunction behaves as an effective δ-doping. An AlGaN/GaN heterostructure is used for the demonstration. The rectifying characteristics of the polarizationinduced GaN HBDs can be tuned by cont...

We use subpicosecond laser pulses to generate and monitor in real time collective oscillations of electrons in a modulation-doped GaAs quantum well. The observed frequencies match those of intersubband spin- and charge-density excitations. Light couples to coherent density fluctuations through resonant stimulated Raman scattering. Because the spin- and charge-related modes obey different select...

We report the observation of the positively charged exciton and of the triplet state of the negatively charged exciton in modulation doped GaAs quantum wells. Applying a gate voltage at high magnetic fields we find that the photoluminescence line of the two-dimensional electron gas smoothly transforms into a negatively charged exciton and not into a neutral exciton. The Zeeman splitting of this...

First-principles simulations have been performed for [001]-ordered Mn/Ge and Mn/GaAs " digital alloys " , focusing on the effects of i) a larger band-gap and ii) a different semiconducting host on the electronic structure of the magnetic semiconductors of interest. Our results for the exchange constants in Mn/Ge, evaluated using a frozen-magnon scheme, show that a larger band-gap tends to give ...

The nonlocal dynamics of electrons in pseudomorphic AlGaAs/GaAs/InGaAs heterostructures with double-sided donor-acceptor doping AlGaAs barriers and additional digital potential short-period AlAs/GaAs superlattices around the doped regions has been theoretically studied. For studied heterostructures, introduction significantly, by 30-40%, increases drift velocity overshot when they enter region ...

A new technique has been developed for measuring the T1 spin lifetime of electrons, and should have near universal applicability among III–V semiconductors. The technique has been applied to a lightly doped GaAs sample with n = 3 × 1014 cm−3. Spin decays were measured for fields from 0.5 to 7 T, at temperatures of 1.5 and 5 K. The spin lifetimes were shorter than expected, possibly due to compe...