氧化鋅奈米線與橫向磊晶成長的氮化鎵之拉曼光譜研究

Abstract

我們探討氧化鋅奈米柱及在載流氣體分別為氫氣、氮氫氣混和及純氮氣下，以氫化物氣相磊晶成長( hydride vapor phase epitaxy : HVPE)氮化鎵厚膜在異質基板上，並使用磊晶側向成長法 (epitaxial lateral overgrowth : ELO )成長的氮化鎵之表面結構與光譜特性，分析型態對光譜的影響。 在氧化鋅奈米柱的研究中，由拉曼散射光譜的分析，我們發現奈米柱的拉曼活性振動模與奈米線相近，綠光二極體基板上的氧化鋅奈米柱的光譜螢光訊號太強掩蓋住氧化鋅的訊號；藍光二極體基板上的氧化鋅奈米柱光譜E2(high) 振動模式 438 cm –1有比較強的譜峰，顯示氧化鋅的結晶品質；光譜上未顯示583 cm –1 峰，說明樣品具有低濃度的氧空缺。 在不同載流氣體下成長的氮化鎵之拉曼散射光譜研究中，我們發現其拉曼活性振動模在平面與橫截面明顯不同，平面的 E2 (high) 振動模強度最大，橫截面則以A1(TO) 振動模強度最大；E2 (high) 峰的變化顯現應力的影響。經由計算雙軸的應力可得在氫氣中的應力比較大約0.81 GPa；在氮氫混和中約0.36~0.51 GPa；在氮氣中則最小為0.38 GPa，皆為壓力的作用。 我們並以電漿子耦合效應的 Impurity-Induced Fröhlich（I I F）機制模擬，在氫氣中的氮化鎵電漿濃度為1 × 1017 cm-3；電漿阻尼常數為150 cm-1；晶格阻尼常數受位置影響約為7~12 cm-1。在氮氫混和中的氮化鎵電漿濃度為1 × 1017 cm-3；電漿阻尼常數為200 cm-1；晶格阻尼常數為7 cm-1。在氮氣中無明顯數據可模擬。

We present the results of the Raman-scattering measurements of ZnO nanorods by self-catalyzed vapor-liquid-solid（VLS）process and GaN microstructures grown by epitaxial lateral overgrowth（ELO）using hydride vapor phase epitaxy（HVPE）. The Raman spectrum of the ZnO nanorods exhibit three sharp phonon peaks at ~ 101,379, and 438 cm-1, corresponding to symmetries E2(low), A1(TO), and E2(high), respectively . It reveals a low concentration of oxygen vacancies in these ZnO nanorods and their high optical quality. By varying the carrier gas composition (hydrogen versus nitrogen), the growth mode of GaN microstructure can be modified during deposition. The Raman-active E2 (high) phonon is found to gauge the strain distributions of the sample, which gives evidence of the biaxial strain of －0.81 GPa, －0.51GPa, and －0.38 GPa in hydrogen, 1:1 mixed hydrogen/nitrogen, and nitrogen content. Moreover, the peak shift and the broadening of the linewidths as well as asymmetric shape observed in A1(LO) phonon agree with those calculated on the basis of the LO phonon-plasmon model, suggesting a low carrier density of 1 × 1017 cm-3 in hydrogen and 1:1 mixed hydrogen/nitrogen content.