**1. Introduction**

The analogy between the hydrogen atom and donor and acceptor dopants in semiconductors has been known for a very long time—see References [1,2] and references therein. However, mainly during the latter half of the past century, in experiments related to conventional semiconductor physics, dopant-atoms have been used as passive elements for several kinds of logic building blocks, for example, P-N junctions [1]. Under this original implementation method, many dopants were implanted in semiconductor materials to obtain a primitive control of their band gap and to create a barrier that could, in turn, be used to control the transition between the OFF state and the ON state (or vice versa) of a transistor made with these materials [1]. However, towards the end of the past century, limitations to this primitive approach to band gap engineering became apparent. Successively, many researchers around the world started to fabricate individual devices, which allowed much better control of the band gap via heterojunctions and other sorts of nanostructures [1,3]. A heterojunction is formed when two di fferent semiconducting materials, typically with a small mismatch on the size of their lattice constants, are deposited one on top of the other. By doing so, it is possible to obtain a better control on the band gap of the materials, and consequently, to achieve fundamental advancements in the properties of optoelectronics devices [1,3,4]. While from their optical points of view, heterostructures fabricated via heterojunctions, such as quantum wells and superlattices, have already demonstrated the ability to achieve many of their electronic potentialities [3], zero-dimensional heterostructures (i.e., quantum dots), have also been introduced [3]. The latter potentially give rise to equivalent individual atoms in a semiconductor environment, and can be used as so-called artificial atoms [1,3–5]. In this context, there is a long list of materials, for example see References [6,7], that have been used for the observation of these exciting features of mesoscopic and "many-body" e ffects. In this short review paper, however, I will limit my discussion on some of the e ffects recently observed in devices fabricated with CMOS compatible materials [4,5].
