Abstract

One of the most relevant phenomena determining the electronic and optoelectronic properties of semiconductors and semiconductor heterostructures is the interaction between charged carriers and lattice vibrations. Especially electron-LO-phonon interaction provides the dominant relaxation and scattering mechanism in polar compound semiconductors. A special class of material, the semiconductor superlattices, recently gained great attention due to the verification of the early prediction of Esaki and Tsu [1] to generate continuously tunable THz radiation from Bloch oscillation [2], where the Bloch oscillation frequency is solely determined by eFd/h (F is an applied electric field and d the superlattice period). Here we report on the first observation of Bloch oscillations in GaAs/Al_0.3Ga_0.7As superlattices with frequencies tuned in resonance with the LO phonon resonance of GaAs at 8.8 THz. These experiments give direct insight into the nature of electron-phonon interaction in semiconductors. In contrast to the assumption that electronic coherence is rapidly destroyed by electron-phonon interaction, we show that the electronic coherence retains and can be transferred to the lattice vibration due to the formation of coupled Bloch-phonon modes.

© 1996 Optical Society of America