Coherent optical nonlinearities and phase relaxation of quasi-three-dimensional and quasi-two-dimensional excitons inZnSxSe1−x

Abstract

. Coherent optical nonlinearities and phase relaxation of quasi-three-dimensional and quasi-two-dimensional excitons in ZnSxSe1 -x/ZnSe structures. Physical Review B, 56(19), 12581-12588. DOI: 10.1103/PhysRevB.56.12581 Coherent optical nonlinearities and phase relaxation of quasi-three-dimensional and quasi-two-dimensional excitons in ZnS We investigate the dephasing of heavy-hole excitons in different free-standing ZnS x Se 1Ϫx /ZnSe layer structures by spectrally resolved transient four-wave mixing. ZnSe layers of 80, 8, and 4 nm thickness with ternary barriers are studied, representing the crossover from quasi-three-dimensional to quasi-two-dimensional excitons. A common feature of the four-wave-mixing signals is the appearance of two components, a prompt signature and a delayed photon echo, which are identified by their different polarization dependencies and decay times. For crosslinear polarized fields, the rapidly decaying signal is attributed to the response of spin-coupled exciton states, with a decay time given by the inhomogeneous broadening. The photon echo is due to a distribution of localized, noninteracting excitons. We determine the exciton-exciton and excitonphonon scattering cross sections for different dimensionalities by the intensity and temperature dependencies of the exciton dephasing. ͓S0163-1829͑97͒02943-3͔

Ultrafast Phenomena in II-VI Semiconductors

“…We find an exciton-exciton interaction parameter γxx of about 4 and 1.1 depending on the negative delay time of the prepump. These interaction parameters are quite similar to the ones found in ZnSe/ZnSSe QWs [1], in wide ZnSe/ZnMgSe QWs [11], in CdTe/CdZnTe QWs [12], and in GaAs/AlGaAs QWs [10]. But, it is a striking result that the interaction parameter in the case of coherent exciton interaction (τ31 = 0 ps) is nearly four times larger than the one for a dephased background population (τ31 = -5 ps).…”

“…This behavior is further illustrated in Fig. 3 where the homogeneous linewidth of the hh exciton is plotted as a function of prepump delay time τ3 1 . On the timescale of the dephasing of the macroscopic polariZation related to the background exciton population, Γ hom drops by about 30% to reach a value close to the one without prepump.…”

“…spectrally broad) laser pulses. It is thus possible to study exciton-exciton interactions in ZnSe QWs solely of 1s hh excitons [1]. The thermalization dynamics of 1s hh excitons within its dispersion parabola can be investigated starting from large center-of-mass momenta, i.e., high initial excess kinetic energies [2,3].…”

Coherent quantum dynamics of excitons in monolayer transition metal dichalcogenides

“…The data are modeled by γ 0 (T ) = γ 0 (0) + γ T , where γ is the exciton-phonon coupling strength. A fit to the data yields γ = 60 µeV K −1 , which is nearly an order of magnitude larger compared to conventional semiconductor quantum wells 57,58 and is a factor of two larger than excitons in bulk TMD InSe. 59 Extrapolated to zero density and zero temperature, the exciton homogeneous linewidth is γ 0 (0) = 1.6 meV (T 2 = 410 fs).…”

“…Compared to semiconductor systems of different composition and dimensionality (such as GaAs and ZnSe quantum wells), broadening due to EID measured here (≡ γ − γ 0 ), when normalized to the exciton Bohr radius, is nearly an order of magnitude larger. 57,58 Enhanced exciton-exciton interactions in TMDs are attributed to reduced dielectric screening in the 2D monolayers.…”