三五族半導體微米捲管及其光電特性研究

Abstract

本論文致力於研究由分子束磊晶系統成長的磊晶薄膜所形成的半導體微米捲管。將含有內建應力的雙層薄膜結構成長於晶格不匹配的基板上，我們可以利用選擇性蝕刻使應變雙層薄膜從基板上釋放而形成微米等級的捲管，並且發展出可以精確控制微米捲管直徑以及形狀、尺寸、位置等條件的製程技術。在本實驗中，我們成功的製作出內嵌有砷化銦量子點的砷化鎵/砷化銦鎵微米捲管。利用特別設計的光激發量測系統，我們可激發微米捲管上的特定位置來量測其發光特性。捲曲的管狀自然形成一環型共振腔，其光學共振模態可被清晰的測得，且模態間距與理論預測相符合。同時我們也量測到次級的縱向模態。僅管沒有測得明顯的雷射閥值，但是不含背景發光訊號的清晰共振模態，顯示此發光訊號極可能就是雷射所致，而雷射閥值極低的原因可歸因於共振腔的體積極小。 此外，我們也製作出利用鋅原子擴散而具有橫向PN接面特性的捲管，以藉此發展電激發的微米捲管雷射。電性量測顯示捲管確實具有PN接面的特性。然而，可能由於不良的歐姆接觸而造成的高串聯電阻，使我們仍無法測得其雷射特性。但只要再進一步地改善製程技術，我們相信在不久的將來電激發捲管雷射是可被達成的。

In this thesis semiconductor microtubes formed by thin epilayers grown by Molecular Beam Epitaxy is studied. Using the built-in strain in a bi-layer structure grown on lattice mismatched substrate, we are able to form micron sized rolled-up tubes by lifting off the strained layers using selective etching. We have developed techniques to precisely control the diameter, shape, size, and position of the microtubes. In this work, GaAs/InGaAs microtubes with embedded InAs quantum dots were fabricated. The light emission properties were studied using a specially designed optical pumping system, which was able to excite the tubes at desired locations. The rolled-up shape forms a natural ring cavity for the emitted light. Resonant modes of the ring cavity were clearly observed with the mode spacing agreeing with the theoretical predictions. Secondary longitudinal modes along the tube were also observed. Although no clear threshold was observed, the clear resonant modes without background emission, indicated very likely that the light emission was actually due to lasing action. The reason that the threshold is low can be attributed to the small cavity volume. We have also fabricated microtubes with a lateral P-N junction using Zn diffusion in an attempt to achieve electrically pumped microtube laser. Electrical measurement indicated the existence of the P-N junction. However, the high series resistance, probably due to poor ohmic contact, prevented us to see any lasing action. Further refinement of the processing techniques should allow us to achieve the electrically driven microtube laser in the near future.