B.J. Yang

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.

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.

Dispersive optical bistability in ZnCdSe-ZnSe/GaAs strained-layer superlattices on reflection at room temperature

The excitonic optical bistability with nanosecond switching time in ZnCdSe-ZnSe/GaAs strained-layer superlattices has been studied on reflection at room temperature. On the basis of the shape of the measured hysteresis loops, photoluminescence and absorption spectra, the origin of the optical bistability is attributed to the effect of excitonic saturating absorption.

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.

Absorptive optical bistability due to impurity nonlinearity in CdS:Cu

Abstract With the excitation of a ps pulse laser we found both the optical bistability and the multi-order bistability in CdS: Cu + crystals. The nonlinear response time is as fast as 150 ps, and the switching time of the second-order bistable loop approaches 80 ps. The technique of the degenerate four wave mixing (DFWM) has been used to investigate the optical nonlinearity related to the Cu + impurity. The third-order nonlinear susceptibility of χ (3) was measured to be 9 × 10 −9 esu.

Optically pumped lasing in ZnSe epilayers grown by OMVPE

Abstract Blue lasing emission in ZnSe thin films under optically pumped excitation has been observed. The films were grown on (1 0 0) GaAs substrates by organometallic vapor phase epitaxy (OMVPE). These epitaxial films have been characterized using low temperature photoluminescence (PL) and electrical transport as well as deep level transient spectroscopy (DLTS) measurements. It has been found that deep level PL bands are strongly dependent on the growth temperature, and the near band edge (NBE) emission predominated the entire PL spectrum only at the growth temperature near 285°C. The lasing emission spectrum from the ZnSe cavity has been measured at 77 K under various excitation levels by the 337.1 nm line of a N2 laser. Only one emission band Es at 445 nm appears under low excitation level. With increasing excitation level a new band P follows at 448.5 nm below the Es band, which is ascribed to the interaction of excitons. The lasing emission from OMVPE films which originates from the P band with 0.75 MW/cm2 threshold power has been reported for the first time and it can be operated up to 150 K.

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.

EXCITONIC PROPERTIES OF ZNSE-ZNCDSE MULTIPLE-QUANTUM WELLS UNDER HIGH-EXCITATION DENSITY

ZnSe-Zn0.78Cd0.22Se MQWs are grown on GaAs(100) substrate by MOCVD. The photoluminescence (PL) under pulsed N2 laser excitation is investigated in detail. The bands observed in PL spectra at 77K are attributed to the n = 1,2 heavy-hole exciton transitions, respectively. In high-density excitation the excitonic recombination is mainly on the exciton interaction, involves the exciton-electron (Ex-x) and exciton-exciton (Ex-Ex) interactions. The stimulated emission due to Ex-Ex scattering is observed at 77K in ZnSe-ZnCdSe MQWs.

Resonant Raman Scattering and Photoluminescence in Zn1-xCdxSe–ZnSe Superlattice

The Raman scattering and photoluminescence from a Zn0.76Cd0.24Se-ZnSe superlattice at room temperature and 77 K have been studied. Two kinds of LO phonon confined modes were observed in detail for the first time, they were ascribed to those of ZnSe barrier layers and Zn0.76Cd0.24Se well layers in the superlattice, respectively. Four orders of LOw multi-phonon modes for well layers, including Stokes and anti-Stokes, and five orders of LOb multi-phonon modes for barrier layers were seen clearly at room temperature. At 77 K every order of LO phonon modes shifts a little toward lower frequency. Three photoluminescence peaks located at 2.478 eV (19990 cm-1), 2.554 eV (20600 cm1) and 2.387 eV (19250 cm-1) were observed at room temperature.