Structural and Optical Properties of InAs Nanowires
Date Issued
2012
Date
2012
Author(s)
Chen, Li-Hsing
Abstract
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.
Subjects
InAs
nanowire
two-step growth
zincblende
wurtzite
Raman
Type
thesis
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