CdSe, ZnSe, (Cd,Zn)Se, and (Zn,Mg)(S,Se) superlattices and coupled quantum wells

This chapter discusses the properties of CdSe, ZnSe, (Cd,Zn)Se, and (Zn,Mg)(S,Se) superlattices (SLs) and coupled quantum wells. The effects described in this section are only those that are expicitly related to the superperiodicity or the interwell coupling of electronic states in narrow-barrier structures. The explicit strain state (pseudomorphic or free standing) of a SL depends on the bufferlayer material, on the composition of wells and barriers, and on the overall thickness of the heterostructure. CdSe/ZnSe digital alloys or short-period SLs have been tested to replace the (Cd,Zn)Se alloy in (Cd,Zn)Se/ ZnSe heterostructures. Low-temperature PL and reflectance are reported for quasi-quaterneries based on (Cd,Zn)Se/MgSe superlattices. The excitonic absorption in ZnSe/ZnS strained-layer SLs as a function of layer thickness or of temperature are illustrated. The chapter also discusses modification of the optical properties by internal and external fields (hydrostatic pressure and magnetic field). The noncentrosymmetric character of (Zn,Cd)Se/ZnSe asymmetric double quantum wells (ADQWs) is exploited for second harmonic generation. (Cd,Zn)Se/ZnSe SLs embedded in an impurity-induced disordered (Cd,Zn)Se alloy show optical confinement in waveguide structures. Finally the chapter presents a brief discussion on transient effects and dynamics, namely, femtosecond pulse propagation, exciton tunneling in ADQWs, and recombination dynamics in nipis.