We report measurements of acoustic phonon emission from a weakly coupled AlAs/GaAs superlattice (SL) under vertical electron transport. The phonons were detected using superconducting bolometers. A peak (resonance) was observed in emission parallel to the SL growth axis when the electrical energy drop per SL period matched the energy of the first SL mini-Brillouin zone-center phonon mode. This peak was mirrored by an increase of the differential conductance of the SL. These results are evidence for stimulated emission of terahertz phonons as previously predicted theoretically and suggest that such a SL may form the basis of a SASER (sound amplification by stimulated emission of radiation) device.

We present measurements of the electron Hall mobility in n-type GaAs1−xBix epilayers. We observed no significant degradation in the electron mobility with Bi incorporation in GaAs, up to a concentration of 1.2%. At higher Bi concentration (≥1.6%) some degradation of the electron mobility was observed, although there is no apparent trend. Temperature dependent Hall measurements of the electron mobility suggest neutral impurity scattering to be the dominant scattering mechanism.

Spiral and pyramidal WS2 domains controllably synthesized through chemical vapour deposition technique exhibit interesting optical properties.

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We have used femtosecond pump-probe techniques to generate and detect coherent transverse and quasitransverse polarized acoustic phonons in GaAs∕AlAs superlattices. Direct generation of transverse phonons is achieved using superlattices grown on the low-symmetry, (311) and (211), crystal planes. The frequency of the generated phonons is determined by the superlattice period and is in the region of 0.4THz. The dependence of the mode structure on the pump polarization suggests that a Raman scattering process is responsible for coherent phonon generation. Using bolometers on the back surface of the substrate, we show that the transverse phonons leak out of the superlattice and propagate over macroscopic distances at low temperature.