以顯微拉曼光譜探悉砷化銦奈米線之晶格動力學

Abstract

本論文嘗試以拉曼顯微光譜，探悉以氣態源分子束磊晶法所生長之砷化銦奈米線其結構及光學特性。本研究達成了對單根奈米線之材料鑑定，並得到可供解析的砷化銦縱向光學、橫向光學、表面光學三種模態。吾人發現奈米線相較於塊材，其拉曼頻譜之光學模態呈現紅移和選擇律的改變。於變功率量測中，吾人並未觀察到模態位置的明顯移動，顯示雷射加熱於吾人奈米線中並不顯著。透過拉曼光譜各組態的量測，吾人認為乃是由奈米線中堆疊變異產生的短暫纖鋅礦結構，其於X(YY)X量測組態可存在、且頻率較低的E2模態混合於吾人所量測到的TO模態中，因而造成了TO模態約3~4 cm-1的紅移。吾人並於X(ZZ)X和X(YZ)X組態中觀測到了由缺陷引起的纖鋅礦B1模態。本研究首次觀察到了快速熱退火對奈米線拉曼模態造成的藍移現象，吾人認為此乃是ZB和WZ結構間之介面應變因高溫釋放之結果；而介面應變對TO、LO模態約有2 cm-1之紅移效果。

In this thesis, the optical and structural properties of InAs nanowires grown by GSMBE have been investigated by μ-Raman spectroscopy. To begin with, the single nanowire signal detection is achieved, and we observed the LO, TO and SO modes of InAs, which are analyzable. Secondly, we discovered that the optical modes of NWs are red-shifted compared with bulk counterparts, and the selection rules are different too. The possibility of laser heating is eliminated via power-variant measurement, in which we haven’t observed mode shifting. By performing measurements in different configurations, we attribute the 3~4 cm-1 redshift of TO mode under X(YY)X to the appearance of E2 mode of Wurzite structure caused by stacking variance in NW. The Wurzite-B1 mode, induced by lattice disorder, is also observed under X(ZZ)X & X(YZ)X. In addition, the blue-shifting of Raman modes after RTA is observed for the first time, and the phenomena is corresponded to the relaxation of interfacial strain between ZB&WZ structures. The redshift caused by interfacial strain is about 2 cm-1 for both TO & LO modes.