In this work, we analyze the optical properties of semiconductor nanostructures and their application in photodetectors and lasers. Graphene with various geometrical structures embedded in boron-nitride lattices is studied as a new material. Quantum cascade lasers and detectors are studied in this thesis.
Chapter 3 investigates the optical properties of armchair graphene nanoribbons (AGNRs) and graphene nanoribbons embedded in boron nitride (BN) lattices. The first principle calculations, the tight-binding model, and the non-equilibrium Green’s function formalism employed in this study are presented in Sec. 3.1. In Sec. 3.2, the optical matrix elements and transition rules are discussed. Dielectric response, quantum efficiency, and photoresponsivity of AGNRs/BN are discussed in Sec. 3.3. Finally, Sec. 3.4 provides concluding remarks for this chapter.
Chapter 4 describes the analytical approach to approximate the wave functions and energy dispersion in zigzag graphene nanoribbons (ZGNRs). The electronic structure of ZGNRs is derived analytically in Sec. 4.1. The wavenumber approximations to reach analytical models for the dispersion relation and the wave function are derived in Sec. 4.2. In Sec. 4.3, optical matrix elements and transition rules of ZGNRs are obtained from the model. The two approximations used in our models and the derived optical properties are discussed in Sec. 4.4. Finally, Sec. 4.5 draws concluding remarks for this chapter.
In chapter 5, graphene superlattice-based photodetectors are discussed. The optical properties of one dimensional superlattices formed by AGNRs embedded in BN superlattices are presented in Sec. 5.1. The line-edge roughness model is described in Sec. 5.2. This chapter is concluded in Sec. 5.3.
In Chapter 6, the application of quantum cascade structures for the MIR and terahertz region is discussed. An optimization and dynamics study of quantum cascade lasers (QCLs) is presented. Section. 6.1 describes the transport and optimization models. In Sec. 6.2, the simulation results for performance optimization are presented and discussed. Dynamics of QCLs is studied in Sec. 6.3. Quantum cascade detectors are presented in Sec. 6.4.
Chapter 7 finally summarizes the thesis with conclusions.