Arrays of Two-Dimensional Islands Formed by Submonolayer Insertions: Growth, Properties, Devices

Ultrathin insertions of a narrow band-gap material in wide band-gap matrices represent a challenging medium in view of aspects of growth phenomena, unique optical properties, and non-trivial approaches for structural characterization. In a very general case ultrathin submonolayer insertions may form arrays of islands due to the principally discrete nature of the growth front. If the islands are large enough, these islands may act as locally formed quantum well (QW) insertions. If, however, the islands' size is comparable to the Bohr radius and the band-gap difference between the insert and the matrix material is large enough, quantum dots (QD) are formed. Realization of the first or the second regime depends on the surface properties of the substrate and the deposit, particularly, on the tensors of the intrinsic surface stress of both materials and on the lattice mismatch. In this work we consider in detail the case of ultrathin CdSe insertions in wide gap ZnMgSSe matrices: that the nominal thickness is chosen below the critical thickness for three-dimensional (3D) island formation. We give an overview of the experimental results available for these structures obtained by submonolayer or about-one monolayer CdSe depositions. A comparison with similar phenomena observed in conventional III-V and III-N systems is given and possible growth scenarios are discussed. We also discuss practical device applications of the structures based on ultrathin insertions for non-traditional devices. Examples of resonant waveguiding and lasing in edge geometry, of surface emitting lasers with low finesse cavities, and of broad-miniband high-frequency Esaki-Tsu anti-dot superlattices are given.