Interactions between coherent optical phonons and excitonic quantum beats in GaAs/AlAs multiple quantum wells: strategy for enhancement of terahertz radiation from coherent optical phonons

Abstract

We have investigated the dynamical properties of coherent longitudinal optical (LO) phonons and excitonic quantum beats in GaAs/AlAs multiple quantum wells with various layer thicknesses, utilizing a reflection‐type pump‐probe technique and an optical gating method with a photoconductive dipole antenna. It is found that the pump‐probe signal of the coherent GaAs‐like LO phonon is markedly enhanced under the energy‐resonance condition of the LO phonon and the quantum beat due to the fundamental heavy‐hole and light‐hole excitons. This enhancement is caused by the coupling between the coherent LO phonon and excitonic quantum beat via the longitudinal polarization; namely, the quantum beat acts as a driving force for the coherent LO phonon. On the basis of this finding, we have demonstrated that the terahertz radiation from the coherent LO phonon is considerably intensified at room temperature by the longitudinal polarization coupling described above. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Frequency Shift of Terahertz Electromagnetic Waves Originating from Sub-Picosecond-Range Carrier Transport in Undoped GaAs/n-Type GaAs Epitaxial Layer Structures

“…In fact, the strong terahertz radiation from the coherent LO phonon is observed in semiconductor superlattices, which originates from the breaking of the translational symmetry by the existence of interfaces. 16,17) In the present i-GaAs/n-GaAs structures, the relatively strong uniform built-in electric field is formed in the whole i-GaAs layer. The formation of the built-in electric field leads to the breaking of the translational symmetry along the growth direction.…”

Quantum beats of type-I and type-II excitons in an InxGa1−xAs/GaAs strained single quantum well

“…This phenomenon can be exploited for potential applications in optodevices and in sources of terahertz electromagnetic wave. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] Typical excitonic quantum beats originate from the impulsive interference between the heavy-hole (HH) and light-hole (LH) exciton states in a QW, and the beating period is determined by the HH-LH splitting energy (DE HH-LH ). The excitonic quantum beats in type-II superlattices have been observed by photoluminescence dynamics under magnetic fields.…”