自發捲曲微米管之製作與光學性質研究

Abstract

我們利用分子束磊晶技術來成長精確厚度的GaAs/InGaAs bilayer。同時在bilayer的下方成長一層犧牲層，當犧牲層被HF蝕刻去除的同時，bilayer會因為晶格常數不匹配而產生內部strain release的效果，而製作出自發捲曲的微米管。我們以磊晶及製程減薄改變bilayer中GaAs層的厚度的方式成功的調變了微米管的直徑大小。我們發現越厚的GaAs會產生越大的直徑，而且只要調變數個nm的GaAs厚度便可產生數個um的微米管直徑的改變。由實驗和理論預測的結果比較，我們發現使用製程或是磊晶調變厚度的結果都與理論預測相當符合。 我們架設一套低溫微螢光激發螢光系統，對微米管做低溫PL的量測。結果發現無論是量子點微米管或是量子井微米管皆會產生Peak紅移的現象，且不同直徑的微米管有著不同的紅移程度。紅移的現象來自於在捲曲之後GaAs層受到了tensile strain而同時GaAs中QW compressive strain release的原因。我們利用一維的model計算得到GaAs層厚度越厚的微米管其晶格常數的改變量較小，strain release的程度也較小。由微米管的PL以及晶格常數估算的結果我們發現直徑的改變來自於strain release的不同。 最後我們發現對微米管的PL作量測當改變不同聚焦景深會得到不同的訊號。藉由本實驗使用之微螢光激發系統可以精確調控制聚焦深度的特性，我們可以利用本系統得到微米管任何位置的訊號。因此未來期望可將微米管應用於生醫方面的量測。

We use MBE technology to grow precise thickness of GaAs/InGaAs bilayer as well as a AlAs sacrifice layer under of it. As the sacrifice layer was obviated by HF solution, the bilayer will roll up spontaneously by strain release caused by lattice constant mismatch. Through this principle, we can fabricate self-rolled up microtubes. We control the thickness of GaAs layer to modulate the diameter of microtubes either by epi or process method and fit nicely with theory prediction. We can produce larger diameter microtubes by using thicker GaAs layer. It’s worth to notice that we can modulate the diameter on micrometer scale by tuning only few nanometers on thickness of GaAs! For understanding photoluminescence of microtubes, we set up a low temperature micro PL system. Measurement result indicates that whether QD microtubes or QW microtubes have red shift phenomenon. Furthermore, we find that different diameter microtubes have different red shift extent. The red shift phenomenon comes from QW compressive strain release as GaAs layer under tensile strain after rolling up. In addition, we estimate the variation of the average lattice constant after bilayer rolling up. We find thicker GaAs layer cause fewer variation of lattice constant that means lesser strain release. Last, we find that PL signal of micotubes would vary from different focus depth. Therefore we can collect PL signal of each location of microtubes by precisely control the focus depth of our u-PL system. Through this result, it’s very promising to apply microtubes to biomedical measurement in the future.