| GaN and its heterostuctures have been intensively studied for wide applications. For example, InGaN/GaN quantum wells (QWs) have been used as active materials for light emitting diodes (LEDs) and laser diodes (LDs) from blue to green region while GaN/AlGaN QWs have been used for ultraviolet region. Meanwhile, nitrides are also very important materials for power electronic devices since such materials hold various advantage over competing semiconductor materials such as Si, GaAs, etc. Due to the above reasons, we believe GaN and its heterostructures will play crucial role for optics and electronics devices as silicon does for electronics. Thus, it is worthwhile to explore possibility of achieving different kinds of newapplications on GaN. This dissertation is focused on optical study on GaN based materials, including GaN thin film, InGaN/GaN QWs, InGaN dot-in-a-wire nanostructures, GaN/AlN QWs, etc. More specifically, in Chapter 2, we report efficient broadband terahertz (THz) generated in InGaN/GaN heterostructures due to spontaneous dipole radiation utilizing the strong internal field. Considering the normalized power, InGaN/GaN heterostructure is one of the most efficient materials for broadband THz generation. The correlated behavior between THz and photoluminescence (PL) has also been discussed. In Chapter 3, we present the study of PL upconversion from a free standing GaN and the mechanism has been attributed to phonon-assisted anti-Stokes photoluminescence (ASPL) if photon energy of pump laser is in the tail of absorption edge. The potential of laser cooling based on such phenomena has been explored. In Chapter 4, we have present detailed PL studies on different kind of nitrides materials including InGaN/GaN QWs, GaN/AlN QWs, GaN thin film and BN powders. In Chapter 5, we explore the possibility of nonlinear generation on GaN. A GaN/AlGaN multilayer waveguide has been designed to achieve transverse parametric conversion. The objective of this dissertation is not only to study the mechanism of optical behavior of GaN based materials, but also to explore the potential application based on these experimental results. |
