D.Z. Shen

Dispersive optical bistability in ZnSe-ZnS/GaAs multiple quantum wells

Abstract Optical bistabilities with different directions of hysteresis loops in the ZnSe-ZnS multiple quantum wells (MQWs) grown by the metal-organic chemical vapour deposition (MOCVD) on GaAs substrates have been observed in transmission at 77 K with nanosecond switching time, for the first time. On the basis of the shape of the measured hysteresis loops, photoluminescence (PL) and absorption spectra measured, the optical bistability in ZnSe-ZnS/GaAs MQWs obtained here are attributed to the dispersive nonlinearity due to the effect of excitonic saturating absorption.

Picosecond optical bistability in ZnSe-ZnTe/CaF2 multiple quantum wells at room temperature

We present the first observation of room-temperature picosecond optical bistability in ZnSe-ZnTe multiple quantum wells (MQWs) grown by metalorganic chemical vapour deposition (MOCVD) on transparent CaF2(111) substrates. On the basis of the direction of the hysteresis loop, the absorption and the energy band structure in ZnSe-ZnTe MQWs, we show that the nonlinear mechanism for the optical bistability of ZnSe-ZnTe MQWs is due to the effect of increasing absorption, which is ascribed to the band gap shrinkage of ZnSe-ZnTe MQWs due to the high density of electrons and holes in the MQWs. The ps switching time can be explained by the electrons excited to the conduction band of ZnTe layer in ZnSe-ZnTe MQWs relaxing quickly to the conduction band of ZnSe layer in this material system.

Multiphonon Raman scattering in ZnSe/Zn0.80Cd0.20Se superlattices

Abstract A study of the multiphonon (MP) Raman scattering in ZnSe Zn 0.80 Cd 0.20 Se superlattices has been performed for the first time. Two kinds of longitudinal optical phonon modes were observed under the excitation of the 457.9 nm (2.71 eV) and 488.0 nm (2.54 eV) lines of an Ar+ ion laser at room temperature. A systematic discussion to distinguish the MP Raman scattering from hot luminescence is presented.

Optical bistability in ZnSe-ZnS superlattices with a Fabry-Pérot cavity

A Fabry-Perot (FP) cavity is prepared by the vacuum deposition method on ZnSe-ZnS superlattices grown on CaF2. Optical bistability (OB) of excitonic origin is observed at a wavelength of 440 nm in ZnSe-ZnS superlattices on CaF2 with FP cavity for the first time.

The study of third order nonlinearities in ZnCdSe-ZnSe/GaAs MQWs using Z-scan

Abstract The third order nonlinearities in ZnCdSeZnSe multiple quantum wells (MQWs) grown by the metal-organic chemical vapour deposition (MOCVD) on GaAs substrates have been studied at room temperature using Z-scan, for the first time. The research result indicates that the nonlinear refractive index n2 in the ZnCdSe-ZnSe/GaAs MQWs is about −5.05×10−5esu. Considering the absorption spectra in ZnCdSe-ZnSe/GaAs MQWs under different pump intensities at room temperature obtained here, the major nonlinear mechanism for the third-order optical nonlinearities in ZnCdSe-ZnSe/GaAs MQWs can be due to band shrinkage effect in the ZnCdSeZnSe MQWs.

Photoluminescence of ZnSe/Zn1 − xCdxSe strained superlattices under hydrostatic pressure

Abstract A study of the photoluminescence (PL) of ZnSe/Zn 1 − x Cd x Se strained superlattices under hydrostatic pressure (0–2.5 GPa) at room temperature has been performed for the first time. The small sublinear dependence of PL energy with pressure for the heavy-hole exciton of the well layers was observed. The pressure coefficients of the PL peak were obtained by least-squares fits to the experimental data. The linear pressure coefficient obtained by calculation is in good agreement with the experimental one.

EXCITONIC EMISSION IN ZNCDSE-ZNSE MULTIPLE-QUANTUM WELLS

Abstract Zn 1− x Cd x Se - ZnSe multiple quantum wells (MQWs) are grown on GaAs (100) substrate by MOCVD. Their photoluminescence (PL) is studied at temperatures between 77 and 300 K. We have observed five emission bands in Zn 0.68 Cd 0.32 Se - ZnSe MQWs under the 457.9 nm line of an Ar ion laser excitation at 77 K for the first time. Three of these bands are attributed to different exciton emission: the n = 1 heavy-hole (HH) exciton transition, the n = 1 light-hole (LH) exciton transiton and the n = 1 HH exciton transiton with the emission of two LO phonons. The two exciton emission bands P 2 and P 3 of n = 1 HH and n = 1 HH with two LO phonons emission can be observed up to 230 K.

Excitonic optical bistability of ZnSe—ZnS/GaAs MQWs on reflection at room temperature

Abstract We present the first observation of room-temperature nanosecond excitonic optical bistability on reflection in ZnSe—ZnS/GaAs multiple quantum wells, in which the switching intensity and contrast ratio for the optical bistability are about 0.6 MW/cm2 and 7 : 1. The research results indicate that the nonlinear mechanism for the optical bistability is due to the excitonic saturating absorption effect.

Second-harmonic generation in ZnCdSe/ZnSe asymmetric double quantum wells

Abstract Second-harmonic generation in ZnCdSe ZnSe asymmetric double quantum wells (ADQW) was observed using the Maker fringe technique. It is due to the noncentrosymmetric characteristics of ADQW, which make X(2) not equal to zero. The birefringence in ADQW was also observed by finding the point of phase match between fundamental wave and second harmonic.

Picosecond optical bistability in ZnSeCdZnSe multiple quantum wells with a Fabry-Pérot cavity

Abstract Excitonic optical bistability with picosecond switching time in ZnSeCdZnSe multiple quantum wells (MQWs) with a Fabry-Perot (FP) cavity is investigated at room temperature. The result indicates that the threshold and switching time for the optical bistability in ZnSeCdZnSe MQWs with a FP cavity are about 210 kW/cm 2 and 50 ps, respectively. On the basis of the excitonic nonlinear theories, excitonic absorption spectra in the ZnSeCdZnSe MQWs under different excitation intensities obtained here, we attribute the major nonlinear mechanism for the optical bistability in ZnSeCdZnSe MQWs with a FP cavity to the phase space filling of excitonic states and excitonic band broadening due to exciton-exciton interactions.