氮化鎵材料是一項重要的材料尤其在藍光頻段的光電元件以及高溫及高壓元件
上的應用。InGaN 三元化合物可使用於光電元件的active region，同時可以調變能階在2.0eV 到3.4eV間。利用光學方式研究材料的載子動態是改善材料成長的第一步也是相當重要的步驟。

由冷激發光譜我們可以用來研究電子由價帶到導帶的傳輸機制。電子由價帶到導帶的傳輸可以分成四個重要的傳輸過程。量測改變雷射出光的實驗，我們可以用以分辨其中兩個過程。於變溫的實驗中我們可以看到光譜強度對溫度的關係以及能階對溫度的關係。利用這項技術，我們量測由工研院所提供的四塊同樣成長速度，不同成長溫度的InGaN樣品。們可以分辨出第一個光譜來自於價帶與導帶間的傳輸或激子到價帶的傳輸，同時第二個光譜來自於defect level到帶間的傳輸。

利用TR-PR 我們可以用來量測樣品的載子生命週期。本實驗裝置為一籃光激發紅光探測系統，我們針對此探測及激發波段研究其對樣品的反射率變化及吸收變化。我們定760nm探測及380nm激發量測上述之InGaN樣品，我們發現PL強度及樣品載子生命週期有一相關性。我們也改變波長量測樣品，我們發現波常對樣品的生命週期變化並不大。

此外，兆赫波穿透實驗也用來萃取GaN樣品的吸收。我們發現兆赫波的波形有一反射對波形這個反射可能來自於兆赫波源及樣品間的反射。最後我們萃取出樣品的吸收，我們發現樣品的吸收並不大。

本論文我們成功的以PL及TR-PR實驗探討InGaN樣品，同時我們發現樣品的PL強度及載子生命週期有一相關性。載子生命期長的樣品其PL強度相對的比較大，於此論文我們認為其來自於非放光性的生命週期較短，而此一機制的PL強度亦相較的比較弱。而兆赫波穿透實驗提供將來我們用來對樣品於此一波段的自由載子吸收做初期的研究。

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.

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