砷化鋁鎵光學特性

本論文以低溫光激發螢光(PL)、變光激發強度PL以及拉曼散射研究AlGaAs塊材的光學特性，這些AlGaAs樣品係以有機金屬化學氣相沉積法成長並已應用於現今的商用微波假晶式高電子遷移率電晶體(pHEMT)晶片中。從低溫PL頻譜可以觀察到各樣品皆存在四個波峰，其中兩個來自於AlGaAs，其餘則為GaAs緩衝層之信號。AlGaAs的低能量波峰其PL峰值能量為1.810±0.001 eV，我們判斷其為施體至受體(donor-to-acceptor, DA)的放光所致；而除了樣品I以外，其餘樣品的高能PL峰值能量皆在1.828~1.829 eV的範圍內，我們認為這是來自於束縛激子(bound exciton, BE)的放光。而樣品I高能量波峰峰值能量僅有1.824 eV，其半高寬值為6.3 meV也大於其餘樣品(3.3~4.5 meV)，因此我們推測樣品I的高能波峰為帶尾侷限化束縛激子放光(band-tail localized bound exciton, LE)所造成。對於變光激發強度PL頻譜的分析，我們透過整體PL強度對光激發強度之線性變化關係瞭解到，樣品I的載子復合主要都發生在AlGaAs磊晶層，顯示此樣品較深的激子束縛限制了激子的移動。而對比樣品的AlGaAs信號在高光激發強度時會出現飽和現象且GaAs緩衝層PL強度較強，後者並與光激發強度成線性關係，這些結果顯示對比樣品AlGaAs用以束縛激子的雜質濃度較低，大部分的激子都擴散到GaAs緩衝層放光。此外我們也利用速率方程針對上述現象加以驗證。在拉曼頻譜分析的部份，我們以空間相關模型(spatial correlation model)來擬合AlAs-like LO模態的半寬，其中樣品I擬合之相關長度(correlation length)為4.7 nm小於其他樣品之值(約5 nm)，顯示其合金成份波動程度最大，此結果與PL相符。由上述實驗結果顯示：樣品I的合金成份波動最為嚴重，其原因可能來自於較低的成長溫度以及較高的五族與三族比例。

關鍵字

砷化鋁鎵；光激發螢光譜；拉曼散射

並列摘要

In this thesis, we use low-temperature photoluminescence (PL), power-dependent PL and Raman scattering spectroscopy to investigate the optical properties of high purity AlGaAs bulk layer grown by MOCVD. These AlGaAs samples have been applied to pHEMT switches for commercial mobile phones. From low-temperature PL, we observed four bands for each sample. Two of them were the signals of AlGaAs, while the rest came from GaAs buffer layer. We attribute the low-energy band at 1.809 ± 0.001 eV to donor-to-acceptor (DA) transition. For all the samples except sample I, grown at the lowest temperature with the highest V/III ratio, we ascribe the high-energy band at 1.828 ~ 1.829 eV to bound exciton (BE) transition. In contrast, the high-energy band of sample I is assigned to band-tail localized bound exciton (LE) transition because of its lower peak energy (1.824 eV) and larger linewidth (6.3 meV). By analyzing the power-dependent PL of sample I, we found that the PL integral intensity of its AlGaAs bands is a linear function of excitation level, suggesting that carrier recombination mainly takes place in AlGaAs layer because the excitons are trapped in the tail states resulting from alloy potential fluctuation. For the contrastive samples, the PL intensity of AlGaAs saturate at high excitation intensity and the PL intensity of GaAs bands is strong and proportional to excitation intensity, indicating that the density of the impurity binding the excitons is low in the AlGaAs layer. As a result, most excitons diffuse to GaAs buffer layer and recombine there. In addition, we also utilize rate equation to verify these phenomena. In Raman spectra analysis, we used spatial correlation model to fit the AlAs-like LO band, and found that sample I has the shortest correlation length (4.7 nm), suggesting its strong alloy potential fluctuation. Finally, on the ground of aforementioned observations, we conclude that sample I has the most serious alloy potential fluctuation which could result from its low temperature and high V/III ratio growth condition.

並列關鍵字

AlGaAs ； Photoluminescence ； Raman scattering

參考文獻

[1] Yu.A. Goldberg and N.M. Schmidt, “Handbook Series on Semiconductor Parameters,” (eds. M. Levinshtein, S. Rumyantsev and M. Shur), London; World Scientific, vol. 2, pp. 1-36, 1999.

[5] M. Miyashita, H. Kizuki, M. Tsugami, N. Fujii, Y. Mihashi, and S. Takamiya, “Metalorganic chemical vapor deposition growth of high-quality AlGaAs using dimethylethylamine alane and triethylgallium-dimethylethylamine adduct,” J. Crystal Growth, vol. 192, pp. 79-83, 1998.

[6] E.F. Schubert, E.O. Göbel, Y. Horikoshi, K. Ploog, and H.J. Queisser, “Alloy broadening in photoluminescence spectra of AlxGa1-xAs,” Phys. Rev. B, vol. 30, pp. 813-820, 1984.

[7] J.E. Cunningham, W.T. Tsang, T.H. Chiu, and E.F. Schubert, “Molecular beam epitaxial growth of high-purity AlGaAs,” Appl. Phys. Lett., vol. 50, pp. 769-771, 1987.

[8] S. Takagishi, H. Mori, K. Kimura, K. Kamon, and M. Ishii, “Epitaxial growth of AlxGa1-xAs by low-pressure MOCVD,” J. Crystal Growth, vol. 75, pp. 545-550, 1986.

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