砷化銦奈米線結構與光學特性研究

Abstract

本論文研究在砷化銦奈米線成長於矽奈米結構中的結構與光學特性。主要分別兩個部分：第一部分透過掃描式電子顯微鏡觀察奈米線的成長情形，探討經由不同的成長方法以及配合矽溝渠結構可以達到成長出定位控制、高密度以及高指向性的砷化銦奈米線。實驗發現當我們使銦分子束入射方向與矽奈米結構長邊指向平行時成長，可以給予成長出的奈米線具有高指向性，但長度不夠長，而當我們成長奈米線並且同時旋轉基板，可以使奈米線整體長度增長，但較不具有指向性，最後我們利用二階段磊晶方式，也就是綜合前面兩者先固定銦分子束入射方向成長奈米線在持續奈米線並且同時選轉基板可結合兩者優點。另外，我們也探討奈米線的成長機制。 第二部分透過穿透式電子顯微鏡觀察砷化銦分子堆積成奈米線時的結構轉換。實驗發現在低溫成長奈米線可使奈米線較易堆疊成閃鋅礦結構，這與原本成長砷化銦薄膜時的結構相同，但在高溫成長奈米線則會易使奈米線轉變成纖鋅礦結構，此結構原本只有以氮為五族的三五族化合物成長薄膜時才易觀察到。在不同的五三比成長條件也會使奈米線堆積成不同結構，在較高五三比中易觀察閃鋅礦結構但在較低的五三比則會使奈米線較易堆積成纖鋅礦。閃鋅礦與纖鋅礦結構堆積轉換於奈米線中的原因可歸因於雙晶及堆錯缺陷。在閃鋅礦結構中，其排列方式為A-B-C排列，若出現雙晶結構則會使閃鋅礦結構中出現微小區域的纖鋅礦結構；反之，在纖鋅礦結構中排列方式為A-B-A-B，若出現堆錯缺陷則會使纖鋅礦結構中出現微小區域的閃鋅礦結構。最後以拉曼量測觀察奈米線光學特性，拉曼量測中，TO聲子模態訊號的增強，此部分可歸因於纖鋅礦結構奈米線貢獻所致。我們亦觀察到奈米線相較於薄膜材料對雷射光入射能量較為敏感，此可歸因於奈米線結構的熱傳導率較薄膜低的關係。此外，纖鋅礦結構的存在也會使TO聲子模態往低能量位移

In this thesis, we study structural and optical property of InAs nanowires growing in Si/SiO2 nanotrench structure by gas source molecular beam epitaxy (GSMBE). There are two subjects in this thesis. In the first subject, we observe the morphology of InAs nanowires by scanning electron microscopy (SEM). We can grow position-controlled and high directional InAs nanowires with high density by different growth method and Si/SiO2 nanotrench structure. In the first method, we let In molecular beam be parallel to the longitudinal direction of nanotrench to grow InAs nanowires and this method can grow high directional nanowires but their length are not long enough. In the second method, we grow InAs and rotate the substrates simultaneously and this method can grow longer nanowires but the orientation of nanowires is worse than the first method. Finally, we combine these two methods and develop a two-step growth method. Namely, we let the first method as the first step and the second method as second step. In addition, we also discuss the growth mechanism of InAs nanowires. In the second subject, we observe the structure transformation of InAs molecules stack in nanowires by transmission electron microscopy. At low growth temperature, InAs molecules will stack in zincblende structure easily and this structure is consistent with growing in InAs bulk while at high temperature, InAs will stack in wurtzite structure easily and this structure is easy to be observed only in nitride-based III-V compounds. Like temperature, V/III ratio also influence InAs stacking in nanowires and InAs molecules stack in zincblende structure at high V/III ratio while stack in wurtzite structure at low V/III ratio. The reason of structure transformation in nanowires can be ascribed to twins and stacking faults. The stacking sequence in zincblende is A-B-C and twins will form a minimal wurtzite in zincblende structure. The stacking sequence in wurtzite is A-B-A-B and stacking faults will form a minimal zincblende in wurtzite structure. Finally, we use Raman measurement to observe property of InAs nanowire. In Raman measurement, the increase of TO mode is ascribed to contribution of wurtzite structure in nanowires. Nanowires have a larger sensitivity to laser power than bulk because of small contact area with substrate. Additionally, wurtzite structure will cause TO mode downshift in nanowires.