We report the growth of self-assembled ErAs islands embedded in GaAs by molecular beam epitaxy. The nucleation of ErAs on GaAs occurs in an island growth mode leading to spontaneous formation of nanometer-sized islands. Several layers of ErAs islands separated by GaAs can be stacked on top of each other to form a superlattice. X-ray diffraction shows superlattice fringes from such samples. Pump-probe measurements indicate carrier capture times as short as 120 fs. These capture times are strongly correlated with the period of the superlattice.

We have grown epitaxial superlattice structures of layers of semimetallic ErAs particles embedded in an InGaAs matrix on (001) Fe-doped InP substrates. Temperature-dependent Hall measurements, x-ray diffraction, and transmission electron microscopy were performed on the materials. The carrier mobility and the temperature dependence of the charge density imply conduction in the InGaAs matrix. We calculate an offset between the conduction-band minimum of the InGaAs matrix and the Fermi level of the ErAs particles that is strongly dependent on the amount of ErAs deposited. As the size of the ErAs particles increases, the Fermi level decreases from ∼0.01 eV above the InGaAs conduction-band edge to ∼0.2 eV below the InGaAs conduction-band edge and the electrical conduction properties change from metallic to semiconducting.

A traveling-wave THz photomixer based on a free-space optical-THz phase-matching scheme is proposed. A dc-biased coplanar strip line fabricated on low-temperature-grown GaAs serves as the active area of the device, and is illuminated by two noncollinear laser beams which generate interference fringes that are accompanied by THz waves. The device with the laser-power-handling capability over 300 mW and a 3-dB bandwidth of 1.8 THz was experimentally demonstrated. The results show that traveling-wave photomixers have the potential to surpass small-area designs.

This article concerns the microstructure of self-assembled ErAs islands embedded in GaAs. The material is grown by molecular beam epitaxy. The nucleation of ErAs on GaAs occurs in an island growth mode leading to spontaneous formation of nanometer-sized islands. Several layers of ErAs islands separated by GaAs can be stacked on top of each other to form a superlattice. A series of such samples were grown with different depositions of ErAs at a growth temperature of 535°C. The microstructure of these samples was investigated by x-ray diffraction and transmission electron microscopy. We find that initially isolated ErAs islands with a diameter of 2 nm are nucleated. With increasing ErAs deposition, these islands branch out and form extended structures. The samples are coherent in growth directions for ErAs depositions up to 1.8 monolayers. At higher ErAs depositions defects are incorporated into the GaAs matrix.

Room-temperature attenuation measurements are made between lambda=0.8 and 10.0 microm on three GaAs epitaxial samples containing layers of ErAs nanoparticles. An asymmetric attenuation peak is observed around 2.5 microm that increases in strength with ErAs density, and is modeled well by a Maxwell-Garnett formulation and semiclassical transport theory. The nanoparticles are assigned a distribution function of oblate spheroids having a minimum volume corresponding to a 1.0-nm sphere. This is consistent with the self-organizing tendency of ErAs in GaAs, and explains the sharp attenuation peak as a spherical-particle surface-plasmon (i.e., Fröhlich) resonance.