Photoreflectance (PR) spectra of a GaN thin film and an AlGaN/GaN heterostructure were measured by using a HeCd laser or a mercury lamp as a pump beam. The wavelengths (£f) of the HeCd laser and the mercury lamp are 325 nm and 253.7 nm, respectively. The energy of the HeCd laser is lower than band-gap energy of AlxGa1-xN (x > 0.2) so that electron-hole pairs cannot be generated in the AlGaN layer. Hence, the PR of the AlGaN was measured by using Argon ion laser (£f=300 nm) or quadrupled Nd:YAG (£f=266 nm) rather than HeCd laser in the previous works. In this work, the mercury lamp (£f=254 nm)was used as the pump beam. The problem with using the mercury lamp as the pump beam is because it is a diffused source so that it cannot be focused to a small spot. Nevertheless, defocused pump and probe beams were used in the PR measurement to improve signal to noise ratio. Hence, the diffused property of the mercury lamp is not a hindrance to the PR measurements.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0729109-003626 |
| Date | 29 July 2009 |
| Creators | Peng, Yu-lin |
| Contributors | Quark Yung-Sung Chen, Dong-Po Wan, Yan-Ten Lu |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0729109-003626 |
| Rights | withheld, Copyright information available at source archive |
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