ABSTRACT
With the development of the fabrication technique of nanostructures, multiform semiconductor structures are fabricated [1]. The twenty-rst century will see a dramatic change in lighting technologies. By 2025, uorescent and incandescent illumination sources should be replaced by more efcient, long-lasting, and versatile light sources, offering more lumens per cm2 and decreasing the consumption of energy for lighting by 29% [2]. The core of such lighting devices, in its simplest form, is a junction, a relatively simple multilayered structure formed by a semiconductor crystal between two higher bandgap semiconductors, which emits light when an electric current passes through it. The localization of carriers in all three dimensions breaks down the classical band structure of the continuous dispersion of energy as a function of momentum. Unlike quantum wells (QWs) and quantum wires (QWi’s), the energy-level structure of quantum dots (QDs) is quite discrete. This unique structure of QDs opens a new chapter both in fundamental physics in which they
9.1 Introduction ..........................................................................................................................307 9.2 Semiconductor Nanostructures .............................................................................................308 9.3 Quantum Dots .......................................................................................................................308 9.4 Semiconductor Nonlinearities ..............................................................................................309 9.5 Nonlinear Optical Susceptibility .......................................................................................... 310 9.6 Second-Order Nonlinearity .................................................................................................. 311 9.7 Quantum Dot Structure under Study .................................................................................... 314 9.8 Quantum Disk Model under Applied Electric Field ............................................................. 315 9.9 Calculated QD Subbands under Applied Electric Field ....................................................... 319 9.10 Density Matrix Formulation of Optical Susceptibility ......................................................... 320 9.11 Results on SONS................................................................................................................... 324 9.12 SHG, SFG, DFG, and OR ..................................................................................................... 328
9.12.1 Sum-Frequency Generation ...................................................................................... 330 9.12.2 Difference-Frequency Generation ............................................................................ 330 9.12.3 Optical Rectication ................................................................................................. 331
9.13 Inhomogeneity in QDs .......................................................................................................... 331 9.14 Results and Discussion of SHG, SFG, DFG, and OR in QDs .............................................. 332 References ...................................................................................................................................... 339
can be regarded as articial atoms and in potential applications as devices [3,4]. The density of states for a bulk material is a function of energy (~E1/2), while in a zero-dimensional (QD) crystal, the density of states is described by a discrete δ-function, (δ(E)) [5], due to the quantum connement effect.
