氮化鎵奈米線中縱光聲子與電漿子的耦合

Coupled LO-phonon and Plasmon Modes in GaN nanowires

游振威(Chen Wei Yu)

指導教授 ： 賈至達 博士

國立臺灣師範大學/理學院/物理學系在職進修碩士班/碩士(2001年)

摘要

由VLS (氣、液、固三相)所製程的氮化鎵奈米線中，n型氮化鎵的電漿為雜質所造成。縱波光學LO(longtidinal optical)聲子與電漿之耦合現象以拉曼光譜之方法測得，對於介於LO、橫波光學TO(transverse optical)聲子間的譜線可以被解釋為較大電漿阻尼下，LO聲子和電漿的耦合效應所造成的結果，並可由CDF(Charge Density Fluctuations)，IIF(Impurity-Induced Fröhlich)兩種機制說明，電漿的介電係數則採用Lindhard-Mermin 的表示式。由程式模擬拉曼散射光譜和實驗結果比對發現，兩種機制都可同時存在並有不同的比例，此比例和入射光能量有關並可由程式擬合，程式擬合發現氮化鎵電漿濃度約在1019 cm-3數量級，阻尼常數約在 200 cm-1 以上，並推測靠近 LO 的峰值由IIF 機制所造成的效果，而非確實LO 聲子的位置，且隨入射光光子能量增加，使得譜線中IIF 效應增強而有偏移現象，並在接近能帶之入射光光子能量，IIF所造成之聲子峰接近LO 聲子的位置。

關鍵字

氮化鎵 ； 拉曼 ； 耦合

並列摘要

The GaN nanowires grown by the vapor-liquid-solid mechanism were studied by Raman scattering. The free electron gas was due to n-type impurities introduced during the growth. The Raman spectra clearly show the coupling of LO phonon and plasmon. The coupling between LO-phonon and plasma can be well explained by CDF (charge-density fluctuation mechanism) and by IIF (impurity-induced Frühlich mechanism). An overdamped plasma model, along with the Lindhard-Mermin dielectric function, was used to calculate the coupling of LO phonon and plasmon. We found it matched with measured Raman spectra, and impurity concentration can be deduced . Plasmon damping constant was over 200 cm-1 and concentration was about 1019 cm-3. The phonon-like peak was deduced by IIF mechanism and shifted when laser energy relatively close to fundamental band gap of GaN.

並列關鍵字

GaN ； Raman ； coupled

參考文獻

5.John R. Reitz, Frederick J. Milford and Robert W. Christy, Foundations of Electromagnetic Theory, edited by John R. Reitz （Addison Wesley Publishing Co.1993）,p.122~123.

3.Y. G. Cao, X. L. Chen, Y. C. Lan, X. P. Xu, and J. K. Liang, J. Mater. Res.15, 267 (2000)

3.C. C. Chen, C. C. Yeh, C. H. Liang, C. C. Lee, C. H. Chen, M. Y. Yu, H. L. Liu, L. C. Chen, Y. S. Lin, K. J. Ma and K. H. Chen, J. Phys. and Chem. of Solids. 62, 1577-1586 (2001)

4.C. C. Chen and C. C. Yeh, Adv. Mater. 12, 738 (2000)

2.C. C. Chen and C. C. Yeh, Adv. Mater. 12, 738 (2000)