我們研究非線性光學半導體GaSe1-xSx (x = 0.00、0.01、0.03、0.14、0.18、0.26、0.37 及 1.00 ) 單晶塊材的光譜性質。首先，GaSe的拉曼散射光譜顯示四個拉曼活性振動模，其頻率位置在134 cm-1、212 cm-1、250 cm-1及307 cm-1，拉曼峰頻率位置隨著摻硫離子濃度上升而有藍移的現象；當x ≧ 0.18 時，我們觀察到多了一個160 cm-1拉曼峰，隨著摻雜硫離子濃度增加而對應到GaS的188.5 cm-1拉曼峰，這些拉曼散射光譜的變化與GaSe1-xSx層狀堆疊結構的改變有緊密的關聯性。此外，我們觀察到光激螢光光譜在x ≧ 0.18 時，其螢光峰的半高寬明顯變寬，且峰值的光子能量大於能隙，推測此時樣品與GaS同屬間接半導體，而多出來的能量即為聲子放射所造成。
我們進一步研究GaSe1-xSx的室溫全頻光譜與變溫穿透光譜，其中紅外聲子吸收峰隨著摻雜硫離子濃度上升而有藍移現象；由於摻雜硫離子後層間距離縮小，電子與離子作用距離較短因此作用力較強，所以造成能隙上升的現象；我們觀察到不同硫離子濃度樣品能隙的溫度變化率，在x ≧ 0.18 時略為上升後下降與低摻雜樣品的變化不同，此結果亦呼應堆疊結構的變化。最後，我們藉由使用第一原理理論計算GaSe在Γ點的聲子振動特性，並與拉曼散射光譜實驗及紅外光活性振動的實驗結果進行比較。

We report the optical properties of GaSe1-xSx (x = 0, 0.01, 0.03, 0.14, 0.18, 0.26, 0.37, and 1.00) single crystals. Room-temperature Raman-scattering spectrum of GaSe exhibits four phonon peaks at about 134 cm-1, 212 cm-1, 250 cm-1, and 307 cm-1. With increasing sulfur concentration, these Raman lines shift toward higher frequencies. When x ≧ 0.18, additional phonon mode appears at about 160 cm-1 and this phonon gradually hardens to 188.5 cm-1 in GaS, reflecting GaSe1-xSx crystallizes in the different kinds of stacking phases as the sulfur doping increases. Moreover, the linewidth of photoluminescence spectra broadens significantly and its peak position becomes larger than the values of energy gap at x ≧ 0.18. These changes are due to the modification of electronic structures when doped with S on Se in GaSe1-xSx.
Additionally, the room-temperature infrared and optical reflectance and transmittance spectra of GaSe show one phonon resonance at about 210 cm-1 and an electronic transition at about 1.98 eV. Notably, their peak positions shift toward higher frequencies with an increase of sulfur concentration. The temperature variation of the values of energy gap reveals different trends at x ≧ 0.18. All of these observables suggest that sulfur doping causes significant changes in the stack phases of GaSe1-xSx. Finally, the first-principles theoretical calculations were used to predict the frequencies of vibrational modes at the Γ point in GaSe, and compare with the experimental results.

[1] P. A. Franken, A. E. Hill, C. W. Peters, and G. Weinreich, 「Generation of optical harmonics」, Phy. Rev. Lett. 7, 118 (1961).
[2] 徐裕奎、陳晉瑋、張振雄、潘犀靈，利用差頻效應在硒化鎵晶體中產生連續可調之兆赫輻射技術及其應用，科儀新知第二十七卷第一期 (2005)。
[3] Wei Shi, Yujie J. Ding, Nils Fernelius, and Konstantin Vodopyanov, 「 Efficient, tunable, and coherent 0.18–5.27-THz source based on GaSe crystal 」, Optics Letters 27, 1454 (2002).
[4] Wei Shi, Yujie J. Ding, Xiaodong Mu, and Nils Fernelius, 「Tunableand coherent nanosecond radiation in the range of 2.7-28.7 μm basedon difference-frequency generation in gallium selenide 」, Appl.Phys. Lett. 80, 3889 (2002).
[5] E. D. Palik, Handbook of Optical Constants of Solids, Academic, NY, I (1985) , II (1991) and III (1998).
[6] T. Dahinten, U . Plodereder, A. Seilmeier, K . L. Vodopyanov, K. R. Allakhverdiev, and Z. A. Ibragimov, 「Infrared pulses of 1 picosecond duration tunable between 4 pm and 18 pm」, Journal of Quantum Electronics 29, 2245 (1993).
[7] Maman Budiman, Tamotsu Okamoto, Akira Yamada, and MakotoKonagai, 「Heteroepitaxy and multiquantum well structure of layeredcompound GaSe/GaSexS1-x on (001)GaAs substrate」, Jpn. J. Appl.Phys. 37, 5497 (1998).
[8] J. A. Giordmaine and Robert C. Miller, 「Tunable coherent parametric oscillation in LiNbO3 at optical frequencies 」, Phy. Rev. Lett. 14, 973 (1965).
[9] 馬英俊，雷射基本原理及應用，p117，1987年3月。
[10] 蘇品書，光科學及其材料，p147，1988年8月。
[11] V. G. Dmitriev, G. G. Gurzadyan and D. K. Nikogosyan, Handbook of nonlinear optical crystal. Springer series in optical sciences, 64 , Springer Verlag, Heidelberg.
[12] G. B. Abdullaev, L.A. Kulevskii, A. M. Prokhorov, A. D. savelev, E. Y. Salaev and V. V. Smirnov. JETP Lett. 16 ,90-92 (1972).
[13] 翁士民，國立臺灣師範大學物理研究所碩士論文，93 年 6 月。
[14] S. A. Ku, C. W. Luo, H. L. Lio, K. H. Wu, J. Y. Juang, A. I. Potekaev, O. P. Tolbanov, S. Yu. Sarkisov, Yu. M. Andreev, and G. V. Lanskii, 「Optical properties of nonlinear solid solution GaSe1-xSx (0 < x < 0.4) crystal. 」, Russ. Phys. J. 51, 1083-1089 (2008).
[15] C. H. Ho,and K. W. Huang, 「Visible luminescence and structural property of GaSe1-xSx (0<x<1) series layered crystals 」, Solid State Comm. 136, 591 (2005).
[16] Ming-Fu Li, Modern semiconductor quantum physics ,p.96, (1994).
[17] N. M. Gasanly, A. Aydinli, and H. Özkan, 「Low-temperature Raman scattering spectra of GaSexS1-x layered mixed crystals」, Cryst. Res. Technol. 37, 1011 (2002).
[18] N. M. Gasanly, A. Aydinli, and H. Özkan, 「Resonant Raman scattering near the free-to-bound transition in undoped p-GaSe」, Cryst. Res. Technol. 36, 1393 (2001).
[19] C. H. Ho, C. C. Wu ,and Z. H. Cheng 「Crystal structure and electronic structure of GaSe1-xSx series layered solids. 」, Journal of Crystal Growth 279, 321 (2005).
[20] J. Pellicer-Porres, A. Segura, Ch. Ferrer, and V. Munoz, 「High-pressure x-ray-absorption study of GaSe」, Phy. Rev. B 65, 174103 (2002).
[21] S. Jandl, J. L. Brebner, and B. M. Powell, 「Lattice dynamics of GaSe」, Phy. Rev. B 13, 686 (1976).
[22] Noritaka Kuroda, Yuichiro Nishina, and Tadao Fukuroi, 「Phonon structures in optical spectra of layer compounds GaSe and GaS」, J. Phys. Soc. Japan 28, 982 (1970).
[23] M. Hayek, O. Brafman, and R. M. A. Lieth, 「Splitting and coupling of lattice mode in the layer compounds GaSe, GaS, and GaSexS1-x」, Phys. Rev. B 6, 2772 (1973).
[24] C. Pere Leόn, L. Lador, K. R. Allakhversiev, T. Baykara, and A. A. Kaya, 「Comparison of the layered semiconductors GaSe, GaS, and GaSe1−xSx by Raman and photoluminescence spectroscopy」, J. Appl. Phy 98,103103 (2005).
[25] N. M. Gasanly, 「Compositional dependence of the Raman lineshapes in GaSxSe1−x layered mixed crystals」, J. Raman Spectrosc. 36, 897 (2005).
[26] H. Yoshida, S. Nakashima, and A. Mitsuishi, 「Phonon Raman spectra of layer compound GaSe」, Phys. Stat. Sol. 59, 655 (1973).
[27] Yu. M. Andreev, V. V. Atuchin, G. V. Lanskii, A. N. Morozov, L. D. Pokrovsky, S. Yu. Sarkisov, and O.V. Voevodina, 「Growth, real structure and applications of GaSe1-xSx crystal. 」, Mater. Sci. Eng. B 128, 205 (2006).
[28] Jia-Min Shieh, Yi-Fan Lai, Yong-Chang Lin, and Jr-Yau Fang, 「Photoluminescence: principles, structure, and applications」, 奈米通訊第十二卷第二期，94年5月。
[29] Charles Kittel, Introduction to Solid State Physics , p189, (2005).
[30] A. Zibold, H. L. Liu, S. W. Moore, J. M. Graybeal, and D. B. Tanner,「Optical properties of single-crystal Sr2CuO2Cl2」, Phys. Rev. B 53, 11734 (1996).
[31] K. L. Vodopyanov and L. A. Kulevskii, 「New dispersionrelationships for GaSe in the 0.65-18μm spectral region」, Optics. Comm. 118, 375-378 (1995).