Z.P. Guan

RAMAN-SCATTERING STUDY OF THE LONGITUDINAL OPTICAL PHONONS IN ZNSE-ZNS STRAINED-LAYER SUPERLATTICES

Raman scattering studies were performed on ZnSe–ZnS strained‐layer superlattices with different strains. In the optical phonon regime, the Raman spectra of the ZnSe–ZnS superlattices with a superlattice axis along [001] show optical phonons confined in the ZnSe well and ZnS barrier layers, and display a two‐mode behavior corresponding to ZnSe‐like and ZnS‐like modes. We report the experimental results, by means of Raman scattering of confined longitudinal optical phonons in ZnSe–ZnS strained‐layer superlattices. The Raman frequency shift dependence on the layer thickness, superlattice period, and interface strain is presented and discussed.

PHOTOLUMINESCENCE OF A ZNSE-ZNS STRAINED-LAYER SUPERLATTICE UNDER HIGH EXCITATIONS

Abstract The luminescence spectra of high density excitons in a ZnSe-ZnS strained-layer superlattice (SLS) have been studied in the temperature range 77–250 K. The photoluminescence (PL) spectrum in the SLS usually has only one near edge emission band Es. The Es band is attributed to free exciton recombination following scattering from electrons in the conduction band. According to whether the binding energy of the free exciton increases as the well width of SLS decreases, it can be explained that why it is difficult to observe the separated P band in the ZnSe-ZnS SLS system.

STIMULATED EMISSION AND LASER OSCILLATION FROM LIGHT-HOLE EXCITONIC STATE IN A ZNSE-ZN0.8CD0.2SE SUPERLATTICE

At 77 K, stimulated emission from n=1 light‐hole excitons in a ZnSe‐Zn0.8Cd0.2Se superlattice is observed and the oscillation mode properties of n=1 light‐hole and heavy‐hole excitons are analyzed. It is noticed that the ZnSe‐Zn0.8Cd0.2Se superlattice with the shorter Fabry–Perot cavity length d has the larger threshold excitation. The threshold of each mode has been determined using its time delay curve.

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.

Growth of high quality ZnSe epitaxial layers on transparent substrates CaF2 by atmospheric pressure metallo-organic chemical vapour deposition

Abstract High quality ZnSe epitaxial layers (epilayers) on CaF 2 (111) transparent substrate have been successfully fabricated for the first time by atmospheric pressure metallo-organic chemical vapour deposition, using dimethylzinc and H 2 Se as sources. The double-crystal X-ray diffraction pattern (111) shows a little shift of ZnSe diffraction peak towards a small diffraction angle, and the full width at half-maximum of the diffraction peak value from its (111) face is about 0.20°. The optical and electrical characteristics of ZnSe epilayers were measured by photoluminescence, scanning electron microscopy and the Van Der Pauw method; the epilayers exhibit a high crystallographic quality and reveal an even mirror surface. All epilayers have high resistivities of up to 10 7 Ω cm. From the analyses on the energy shift of the luminescence line, a compressive stress has been found in the epilayer sides of these heterostructures. This is consistent with the stresses predicted for a lattice between mismatch the ZnSe epilayer and the CaF 2 substrate.

The luminescence of mercury-like ions alkaline earth sulfides

Abstract The luminescence of mercury-like ions in alkaline earth sulfides is reported, the results show that the luminescence spectra present certain regularity. In CaS two luminescent centers are observed for Pb2+ and Bi3+ ions respectively. Energy transfer phenomena from mercury-like ions or host lattice to Eu2+ in MS are discussed.

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 in ZnSe/ZnS planar waveguide

Non-linear absorption and optical bistability with increasing incident light intensity are obtained at room temperature in ZnSe/ZnS planar waveguide grown by metal-organic chemical vapour deposition for the first time. According to the peak position of absorption spectra and photoluminescence, the optical non-linearity and bistability are attributed to excitonic optical non-linearity owing to the effect of excitonic saturating absorption.

The study of lattice strain and high-resolution transmission electron microscopy in ZnSe-ZnS strained-layer superlattices

The structural properties of ZnSe-ZnS strained-layer superlattices (SLSs) grown on GaAs (100) by atmospheric-pressure metalorganic chemical vapor deposition (AP-MOCVD) were studied using high-resolution transmission electron microscopy (HRTEM). The type and distribution of the defects in ZnSe-ZnS SLS are related to the surface quality of GaAs substrate, of the buffer layer and the thickness of each layer for ZnSe and ZnS in SLS. In this work we noticed that there are stacking faults (SFs), mismatch defects (MDs) and microtwins (MTs) in ZnSe1-xSx buffer layer at interfacial steps due to the GaAs surface not being smooth, and the dislocation can penetrate the ZnSe-ZnS SLS layer.

Excitonic transition of (ZnSe-ZnS)/CaF2 strained-layer superlattices under lower excitation

Abstract A photoluminescence (PL) study of ZnSe-ZnS strained-layer superlattice (SLS) on a transparent substrate, CaF 2 , grown by atmospheric pressure metalorganic chemical vapour deposition (AP-MOCVD) is presented. Two absorption bands and three emission bands in the SLS were observed for the first time under low excitation. The origin of some bands might be ascribed to the excitonic transition of n = 1 heavy and light hole.