Coherent Propagation and Many-Body Effects of Exciton Masses at Semiconductor Interfaces

点击翻译按钮获取中文摘要

In our research, photoinduced high-density effects on excitons and phonons, and their coherent propagation at quasi tow-dimensional interfaces in semiconductors have been studied from experimental and theoretical aspects.In layered crystals BiI_3, GaSe, and PbI_2, we have studied spatial and temporal behavior of high-density exciton masses and their nonlinear optical responses. In BiI_3, extraordinarily large spatial expansion of the excitons confined in a tow-dimensional stacking fault interface (SFE) was observed in the space- and time-resolved photoluminescence above a threshold excitation density. The degenerate four-wave-mixing (DFWM) light induced by spatially isolated two laser-light spots tuned to the SFE state on the sample surface was emitted owing to the coherent transport of the exciton mass from one to the other exciting spot sites showing the SFE-polariton masses being in a Bose-condensed phase. In GaSe as well as PbI_2, it turned out that heavy photo-excitation brings ab … More out recoil luminescence due to scattering with the other excitons or carriers in competition with the biexciton formation.For the excitonic properties and coherent-phonon phenomena in superlattices (SLs), we have obtained the following results. (1) In GaAs/AlAs type-II SLs, where the electron and hole are spatially separated in the AlAs and GaAs layers respectively, the density relation of the excition-biexciton system in the decay process is dominated by Bose-Einstein statistics, which results in a threshold-like increase in the biexciton density. (2) In GaAs/AlAs type-I SLs, the transformation process from the biexciton to the electron-hole-plasma phase is revealed, connecting with the band-gap renormalization due to high-density carriers. (3) In InAs/GaAs SLs, the photoexcited plasmon couples with the GaAs-like coherent-LO phonon through the miniband state.We have theoretically studied macroscopic quantum phenomena in an interacting dilute quasi-two-dimensional Bose gas of excitons in a type-II semiconductor quantum wells and clarified its ordered states, elementary excitations and mechaisms of phase transitions. Less