Chapter III - CdTe-Based Nanostructures

Abstract

This chapter illustrates the up-to-date know-how in the molecular beam epitaxy (MBE) growth of CdTe-based heterostructures. It induces for the II-VI QDs a 2D–3D transition, which occurs after and not during the growth by the rearrangement of a strained 2D layer. This morphology transition under a fixed amount of deposited material can be understood as a surface energy variation obtained by exposing the II–VI layer to a large quantity of the group-VI element. This method allows one to avoid a plastic relaxation and to get coherent grow QDs according to deposit an amount of material less than the one predicted by the plastic critical thickness for astandard SK transition occurring during the growth. The know-how to control the dimensionality of CdTe-based nanostructures, nowadays, CdTe and CdSe nanowires are also performed by MBE using metal droplets as a catalyst to initiate and control the one-dimensional growth mode Low-dimensional structures based on II–VI semiconductors show strong excitonic effects and large optical nonlinearities. Among II–VI systems, the CdTe/CdZnTe quantum well one has been intensively studied due to its interesting fundamental properties such as, for example, a large value of the excitonic Rydberg and large strain splitting of the valence band. This latter effect induces that the lowest energy transitions are spatially direct (type I) for heavy-hole excitons and spatially indirect (type II) for lighthole excitons. The robustness of the exciton Rydberg in II–VIs explains why it was possible to evidence, in 2D CdTe heterostructures, original quantum effects, such as the exciton centre-of-mass quantization, the strong coupling in a 2D microcavity leading to the Bose–Einstein condensation of polaritons, the first observation of the trion, and the tunneling of excitons as a whole.