Guangyou Yu

Carrier tunneling in a novel asymmetric quantum well structure

Based on the carrier tunneling effect, a novel asymmetric quantum well is designed to improve the carrier injection for a type I quantum well. Two type II quantum wells were chosen to provide the electrons and holes for the type I quantum well via carrier resonant tunneling, respectively. Under the condition that both electrons and holes have fast tunneling rate, the carrier recombination in the type I quantum well can be enhanced. In order to optimize the structure, the small coupling barrier width, energy level resonance and small energy level width should be chosen simultaneously.

Investigation on the Phase Transition Behaviors in Pb0.97La0.02(Zr0.42Sn0.40Ti0.18)O3 Ceramics

Phase transition behaviors in Pb0.97La0.02(Zr0.42Sn0.40Ti0.18)O3 (PLZST) ceramics were investigated by means of polarization, pyroelectric and dielectric studies. The polarization analysis indicated that the initial state of this PLZST ceramics is ferroelectric (FE) and it transforms into a narrow antiferroelectric (AFE) phase when the temperature approaches 120°C. This phase transition behavior was further confirmed by the pyroelectric and dielectric measurements. What is more, after poled, the frequency dispersion in dielectric constant (ϵ) and dissipation factor (tanδ) induced by La modification disappeared.

Temperature-dependent exciton recombination in asymmetrical ZnCdSe/ZnSe double quantum wells

Temperature-dependent exciton recombination in asymmetrical ZnCdSe/ZnSe double quantum wells is studied by recording photoluminescence spectra and photoluminescence decay spectra. The exciton tunnelling from the wide well to the narrow well and the thermal dissociation of excitons are two factors that influence the exciton recombination in this structure. In the narrow well, both of the two processes decrease the emission intensity, whereas, in the wide well, these two processes have contrary influences on the exciton density. The change of the emission intensity depends on which is the stronger one.

Spontaneous and stimulated emission in ZnCdSe/ZnSe asymmetrical double quantum wells

The spontaneous and stimulated emission in ZnCdSe/ZnSe asymmetric double quantum wells have been studied. The exciton photoluminescence both in the narrow well and in the wide well is influenced by two factors, the exciton tunneling and the thermal dissociation processes. The change of the emission intensity is determined by the stronger one. The carrier tunneling through the thin barrier is conductive to the stimulated emission from the wide well, and the threshold can be lowered by optimizing the structure.

Laser action in ZnCdSe/ZnSe asymmetric double-quantum-well

Lasing from the wide well of ZnCdSe/ZnSe asymmetric double-quantum-well structures is studied. Owing to the difference of the energy levels between the wide well and the narrow well, the carriers tunnel from the narrow well to the wide well, which can influence the emission effectively. The carrier tunneling is conducive to lasing from the wide well. The threshold can be lowered by optimizing the structure.

Photoluminescence characterization of ZnTeSe epilayer at room temperature

ZnTexSe1-x epilayers with composition x equals 0.005, 0.02 and 0.16 have been grown by low pressure-metal organic chemical vapor deposition (LP-MOCVD) method. Two bands (blue S1 and green S2) were observed in the ZnTexSe1-x epilayer with composition x equals 0.005 at room temperature (RT). With increasing composition x greater than 0.02, the S1 band disappeared and the S2 band was the main emission in photoluminescence (PL) spectra. The origin of the S1 and S2 bands was attributed to excitons trapped at Te1 and Ten (n greater than or equal to 2) cluster.

Impurity process in ZnCdSe/ZnSe multiple quantum wells

At high excitation intensity the photoluminescence (PL) spectra of ZnCdSe/ZnSe multiple quantum wells were studied, which showed strong excitonic emission and a broad emission band at low energy side. The dependence of the broad emission band on excitation intensity shoed obviously that the broad emission band is related to impurity. In time resolved luminescence spectra, with increasing the delay times (ns), the broad emission band shifts to low energy side and full width at half maximum decreased, which showed the typical characteristic of donor-acceptor pairs (DAP) emission. And then, the reason that the excitonic emission peak and the DAP band decay with same speed was discussed and it was attributed to the free carriers relax effect.

Saturating refractive nonlinearities and optical bistability in ZnSe/CdZnSe MQWs at room temperature

The excitonic nonlinear refractive index was calculated by using Kramers-Kronig relation and the saturating absorption of ZnSe/CdZnSe multiple quantum wells (MQWs) was studied under different pump intensities. The maximum nonlinear refractive index change is about -6.19 X 10-3. Excitonic optical bistability in ZnSe/CdZnSe MQWs is investigated at room temperature. The result indicates that the threshold and contrast ratio for the optical bistability in ZnSe/CdZnSe MQWs are about 210Kw/cm2 and 2:1, respectively. On the basis of the excitonic nonlinear theories and excitonic absorption spectra in the ZnSe/CdZnSe MQWs, we attribute the major nonlinear mechanism of the optical bistability in the ZnSe/CdZnSe MQWs to the phase space filling of excitonic states and excitonic band broadening due to exciton-exciton interactions.

Carrier tunneling in ZnCdSe/ZnSe asymmetric double-quantum-well structure

Optical characteristics of ZnCdSe/ZnSe asymmetric double- quantum-well structure grown by LP-MOCVD were studied. By analyzing the photoluminescence spectra, we found that the excitation power and temperature could influence the tunneling of the excitons, and due to different tunneling time of electrons and holes, space-charge effect was observed.