Abstract
The group Ⅲ-nitride wide bandgap semiconductors have been recognized recently as very important materials for fabricating optical-electronic devices in the blue/UV region and electronic devices operating under high-power and high temperature conditions. The ternary Ⅲ-nitride compound InGaN is a promising candidate for the active layer for blue light emission because its band gap varies from 2.0eV to 3.4eV depending on the indium mole fraction. Optical transition and optical studies on carrier dynamics is the first step and important part in improving the quality for thin films. Photolumisence (PL) could be used to investigate the transition mechanisms for the materials. Time-resolved measurement is a key technique to study the dynamic processes. Terahertz (THz) spectroscopy is a powerful technique for the study of materials in the frequency range from a few tens gigahertz to a few terahertz. In this thesis PL, TR-PR and THz transmission experiments were performed on InGaN and undoped GaN. There are two peaks in the PL spectra for InGaN; the first peak is believed to be band-to-band transition and the second peak is believed to be band to deep level transition. We found that the intensity of these PL peaks can be correlated with the carrier relaxation time extracted from TR-PR measurements. THz transmission experiments were used to extract the information of absorption for undoped GaN. We found that there were no absorption peaks in the spectra range investigated. Our studies on GaN an InGaN may provide more experimental verification of the optical transition mechanisms in group-III nititrides, which were proposed in the literature.