低維度氮化銦:成長視窗及導電高分子異質接面

Abstract

本論文目的，主要係探討利用低維度氮化銦材料與導電高分子以形成異質接面，並以此接面作為近紅外線偵測器的應用與電荷分離之機制研究。其中，低維度氮化銦材料包括一維奈米材料與薄膜材料，亦將界定出這些不同奈米結構的成長視窗，並參考文獻探討可能之成長機制。 本論文利用有機金屬化學氣相沉積方法來合成氮化銦奈米結構，並使用氣相-液相-固相成長機制來闡釋其形成的原因，而其中包含了液態合金催化劑擴散以及表面擴散兩種成長機制。此外，在金屬-氮化銦與導電高分子-氮化銦接面進行光電流與光反應量測，由光反應的靈敏來探討其元件的缺失；同時，使用靜態與動態螢光光譜來解析在異質接面發生的電荷分離現象，並更進一步利用電容-電壓量測來模擬出導電高分子的位能分佈，以找出電荷分離的機制。 因液態合金催化劑之擴散機制，使合金催化劑的大小決定了奈米線半徑大小；相對地，奈米柱呈現半徑逐漸縮小的現象，而這可以歸因於表面擴散的成長機制所導致。藉由與薄膜材料的活化能比對，可以發現一維奈米材料與薄膜材料均係呈現平面式成長，並且，對照奈米線與奈米柱的成長速率，本論文發現奈米柱需要較長時間來進行奈米結構初始成長。 由光電流產生在金屬-氮化銦接面研究可知，表面氧化層會抑制光電流產生；此外，光電流在導電高分子-氮化銦接面可以因此而增大，然而，於低偏壓下，由於熱游離電子使得此異質接面無法形成明顯的驅動電壓。本論文亦發現，由於氮化銦表面具有表面電荷累積，使得表面具有很強的內建電場，故造成導電高分子位能重新分佈導致電荷分離。 本論文認為，如何有效地降低氮化銦的載子濃度，並藉由表面修飾方法以控制表面位能彎曲程度，將會是未來影響氮化銦元件發展的關鍵。

The aim of this thesis is to form the heterojunction based on low-dimensional indium nitride and conducting polymer. A number of studies have been done to investigate the near infrared photodetector and the mechanism of charge separation using this hetero-junction. This thesis, by reference to the relevant literature, defines the growth windows of different nanostructures, including one-dimensional nanostructures and thin films. Possible growth mechanisms are also considered thoroughly. In this thesis, the low-dimensional indium nitride is synthesized by using metal-organic chemical vapor deposition and vapor-liquid-solid growth mechanism, including liquid alloy and surface diffusion. The photocurrent and photoresponse measurement are performed in the junctions of metal/indium nitride, and conducting polymer/indium nitride. The potential application of the devices is evaluated by measuring the photoresponse sensitivity. Meanwhile, this thesis analyzes the phenomenon of charge separation by using static and dynamic photoluminescence spectroscopy. Potential distribution in conducting polymer is then modeled according to capacitance-voltage measurement. Because of liquid alloy diffusion, the diameter of nanowire is determined by alloy droplet. By contrast, the phenomenon of nanorod tapering can be attributed to surface diffusion. According to activation energy, the one-dimensional nanostructures follow planar growth, which is the same as the case for thin films. Also, the initial growth time of nanorod is longer than that of nanowire in accordance with growth rate. Thus, photocurrent will be suppressed by surface oxide layer based on the studies of photocurrent generation in metal/indium nitride. In addition, due to the junction between conducting polymer and indium nitride, photocurrent will be enhanced. However, in lower bias condition, the current-voltage curve does not show apparent built-in potential because of thermionic emission mechanism. Because the surface accumulation layer exists in indium nitride which results in strong built-in electrical field, it induces potential rearrangement in conducting polymer for charge separation. To conclude, this thesis argues that, to decrease the carrier concentration of indium nitride and control the magnitude of surface band bending would be indispensable for development of InN-based devices in future.