Terahertz driven amplification of coherent optical phonons in GaAs coupled to metallic dog-bone resonators

Abstract

Two-dimensional terahertz spectroscopy on an AlAs/GaAs nanostructure covered by field-enhancing dog-bone resonators shows signatures of coherent optical phonon amplification. Amplification is due to stimulated phonon emission by a terahertz-driven electron current.

Non-equilibrium dynamics, materials and structures for hot carrier solar cells: a detailed review

“…Calculated coherence lengths of LO phonons in bulk GaAs vary with temperature and evolve from d LO coh (GaAs) = 300 Å (T = 1 K) via 35 Å (10 K) to 23 Å (300 K) [74], the latter matching recent experimental values quite well [75]. For TO phonons in bulk GaAs, d TO coh (GaAs) = 70 Å (T = 1 K) via 5 Å (10 K) to 12 Å (300 K) were obtained from [74].…”

“…For TO phonons in bulk GaAs, d TO coh (GaAs) = 70 Å (T = 1 K) via 5 Å (10 K) to 12 Å (300 K) were obtained from [74]. Confinement of optical phonons in GaAs epi-layers by coherence under THz field excitation was shown in experiment for d GaAs = 30 Å [75] which is a factor of 4 below the coherence length of acoustic phonons in GaAs. The authors also stated that the creation of a quasi-stationary electron/hole population with inversion presents a challenge because of the huge concomitant heat load which was solved by using a single 30 Å GaAs QW as an optical phonon resonator on a 300 µm thick GaAs wafer which acted as a heat sink, separated by a 400 Å thick AlAs spacer.…”

“…The experimental value of d QW (GaAs) = 30 Å for optical phonon confinement measured at T = 300 K [75] has to be seen in the context of electronic properties of such QWs. The exciton radius is derived from effective masses of electrons and holes m n eff , m p eff and the relative dielectric constant of GaAs [26] to r exc = 114 Å.…”

“…The exciton radius is derived from effective masses of electrons and holes m n eff , m p eff and the relative dielectric constant of GaAs [26] to r exc = 114 Å. Hence, quantum confinement occurs for d QW ≤ 228 Å, exceeding the value of d QW (GaAs) = 30 Å obtained above [75] by about 8-fold. This spatial discrepancy 15 Confining acoustic phonons is still important for electrothermal energy converters to diminish their thermal conductivity.…”

Absorption and Photoluminescence of Silicon Nanocrystals Investigated by Excited State DFT: Role of Embedding Dielectric and Defects

“…[ 45 ] The covalent Si—Si bonds would get excited by a displacement charge mechanism which provides much weaker electron–/hole–phonon coupling, [ 86,87 ] though, due to an increasing ionization of Si atoms towards the interface originating from charge transfer to the dielectric, a small partition of optical phonon emission may also proceed via the Fröhlich mechanism. The strong electron–/hole–phonon coupling and propagation likely exceeds the coherence lengths of optical phonons in semiconductors of ≈ 23 – 30 Å, [ 88,89 ] thereby considerably promoting the diverse phonon decay mechanisms from optical into acoustic phonon modes. As a result, the Bose–Einstein occupation factor of the optical phonon DOS does not grow much beyond its intrinsic value obtained in thermal equilibrium.…”