本論文主要探討PVK緩衝層對於氧化鋅/氧化亞銅異質接面光二極體表現之研究。首先，多晶的氧化亞銅薄膜電鍍在ITO的玻璃基板上，接著在氧化亞銅薄膜上旋轉塗佈PVK薄膜，定義好濺鍍於PVK薄膜上之氧化鋅晶種層後，再利用水浴法合成氧化鋅奈米柱陣列，PVK薄膜是用來當作電子阻擋/電洞傳輸層。掃描式電子顯微鏡和X光繞射儀用來對備製的元件進行表面形貌、薄膜界面、厚度與晶體結構之分析。
接著，我進一步量測及分析PVK緩衝層對氧化鋅/氧化亞銅異質接面二極體光電特性之影響。在紫外光的照射下,氧化鋅/PVK/氧化亞銅和氧化鋅/氧化亞銅光二極體在-0.5 V偏壓下光暗電流比分別為133和3.99。此外，氧化鋅/氧化亞銅的紫外光-可見光拒斥比為1.735，而當有PVK層的情況下紫外光-可見光拒斥比被提升至350，主要歸功於有較高的紫外光電流放大以及產生低的可見光光電流。
在上述的結果中，我發現幾個新穎的特徵:(a) 紫外光所產生的電洞載子能夠穿越PVK層傳輸至氧化亞銅層;(b) PVK緩衝層具有顯著地抑制逆偏漏電流,致使有較大的光電流放大效果;(c) 利用PVK層可改善紫外光對可見光拒斥比並達到高靈敏度的紫外光偵測能力。

In this dissertation, I investigate the effects of a poly-(N-vinylcarbazole) (PVK) intermediate layer on the performance of n-ZnO nanorods/p-Cu2O heterojunction photodiodes. Polycrystalline p-Cu2O thin film was electrodeposited on a commercial available ITO/glass substrate. An organic PVK layer was then spin-coated onto the Cu2O film followed by ZnO nanorods synthesis on a patterned ZnO seed layer using a chemical bath deposition (CBD) method. The PVK layer acts as an electron blocking/hole transporting layer between the ZnO and the Cu2O films. Meanwhile, the ZnO/Cu2O heterojunction photodiodes without PVK layer was also fabricated for comparison. A scanning electron microscope was used to observe the surface morphologies and cross-sectional images of the samples. Crystalline phase and orientation were determined by x-ray diffraction patterns obtained from an x-ray diffractometer.
To analyze the role of PVK, I measured the electrical and optical properties of the photodiodes. Under UV light illumination, the photocurrent/dark current ratios of the n-ZnO/PVK/p-Cu2O and n-ZnO/ p-Cu2O photodiodes at -0.5 V bias are 133 and 3.99, respectively. The n-ZnO/p-Cu2O exhibits a UV-to-visible rejection ratio (R-360nm/R-450nm) of approximately 1.735 under a -0.5V bias. When the PVK buffer layer is inserted between the n-ZnO and the p-Cu2O layers, the rejection ratio increase to 350 owing to higher UV photocurrent/dark current contrast ratio and lower photocurrent generation under visible light illumination.
On the basis of above results, several novel features have been demonstrated for the first time: (a) UV photo-generated holes can effectively transmit through the PVK layer to the p-Cu2O layer; (b) insertion of a PVK buffer layer significantly minimize the reversed-bias leakage current, which leads to a large amplification of the photocurrent; and (c) the device with a PVK buffer layer can improve UV-visible responsivity ratio and achieves better UV detection sensitivity.

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