Superlattices and various quantum structures obtained thereof have drawn much attention in past decades [46]. Commensurate or pseudomorphic junctions of two different semiconductors have been grown layer by layer to form a periodically repeating superlattice structure with sharp lattice-matched interface [96,174,175]. Owing to the band discontinuities at the interface, they behave as a multiple quantum well structure according to the effective mass theory. Electrons confined in these quantum wells exhibit two-dimensional electron-gas behavior with interesting quantum effects [46]. Two-dimensional conduction-band electrons (valence-band holes) confined to the wells have displayed a number of electronic and optical properties [96,174–177].
In this chapter, the optical properties of hydrogen-passivated armchair graphene nanoribbons superlattices (HSLs) and boron-nitride-passivated armchair graphene nanoribbons superlattices (BNSLs) are studied.
The results indicate high responsivity and quantum efficiency as well as long wavelength operation which render these devices as potential candidates for future photodetection applications.
Figure 5.1 shows the structure of the studied superlattices. In the structure shown in Fig. 5.1(a) the dangling bonds of edge carbon atoms are saturated by hydrogen atoms, whereas in the structure shown in Fig. 5.1(b) the semiconducting region (formed by carbon atoms) is surrounded by BN. Throughout this study, the structures in Fig. 5.1(a) and (b) are used as main structures which are referred to as HSL(11) and BNSL(11), respectively. The numbers inside the parentheses represent the number of carbon atoms along the width of the wider part of the superlattice (nw).
Lengths of 8acc and 7acc are considered for the well and barrier regions, respectively, where acc = 1.42 Å is the carbon-carbon bonding distance. To investigate the optical properties of these superlattice structures, the non-equilibrium Green’s function (NEGF) formalism introduced in Sec. 3.1.3 along with a tight-binding (TB) model for the electronic bandstructure (Sec. 3.1.2) are employed. The TB parameters are modified to match the results with first principle calculations. For first principle calculations we employed the SIESTA package [152]. The parameters used for the DFT calculation are given in Sec.3.1.1.
