Miniband structures and effective masses of GaAs/AlAs superlattices with ultra-thin AlAs layers

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

“…In fact, we demonstrated that the intensity of the coherent LO phonon in the (35, 35) MQW is resonantly increased at the LH-exciton energy [2]. Thus, the similarity between the pump-energy dependence of the coherent LO phonon and that of the excitonic QB in the (18,18) MQW suggests that the two coherent modes couple with each other. Figures 3(a) and 3(b) indicate that the temperature dependence of the integrated FT intensity of the excitonic QB and that of the coherent LO phonon in the (35, 35) and (18,18) MQWs, respectively, where the pump energy was tuned to the center energy between the HH and LH excitons.…”

“…On the other hand, in the time range longer than 1.5 ps, the period of the weak oscillation is 113 fs, which is the same in the three MQWs. The amplitude of the weak oscillation after 1.5 ps in the (18,18) MQW is about 20 times larger than that in the (35, 35) MQW, while the amplitude of the strong oscillations hardly changes with the layer thickness. , it is evident that the peak frequencies are the same in the three MQWs: 8.8 THz corresponding to the LO-phonon energy of GaAs (E LO ).…”

“…The ratio of the FT intensity of the coherent GaAs-like LO phonon to that of the excitonic quantum beat is 1.7×10 −2 in the (18, 18) MQW and 2.6×10 −5 in the (35, 35) MQW. The FT intensity, which corresponds to the square of the oscillation amplitude, of the coherent GaAs-like LO phonon in the (18,18) MQW is about 650 times stronger than that in the (35, 35) MQW. Thus, the intensity of the coherent LO phonon is markedly enhanced in the (18,18) MQW.…”

“…Figure 1(a) shows the time-domain signals of the (18,18), (25,25), and (35, 35) MQWs at 10 K, where the pump energy was tuned to the center energy between the HH and LH excitons in each MQW. The splitting energy of the HH and LH excitons (∆E HH-LH ) are also denoted in Fig.…”

Photoluminescence from excitons at the mini‐Brillouin‐zone boundary in a GaAs/AlAs superlattice

“…In order to detect the PL from the π-point exciton that has a very fast relaxation process in momentum space, we measured time-resolved PL (TRPL) spectra with a streak-camera system. Photoreflectance (PR) spectroscopy, which is much sensitive to detect the optical transition at the singular point of the density of states [5,6], also used to characterize the optical transition energies at the Γ and π points: clear observation of the transition of the heavy-hole exciton in the first (n = 1) miniband at the π point, H11(π), in addition to the Γ-point exciton, H11(Γ). Under a condition that an excitation energy is higher than the H11(π)-transition energy, we have never observed the PL band of the H11(π) transition.…”