鈣鈦礦奈米薄片之光電特性及電晶體研究

Abstract

本研究提出將三維結構有機無機混和型鈣鈦礦的厚度降低至數奈米的實驗方法以及後續將其製作成元件觀察鈣鈦礦薄片的光電特性。在本研究中，有別於其他文獻常使用的化學氣相沉積法，使用溶液的方式，藉由調整實驗條件，例如：轉速、旋轉時間、是否臭氧清洗機處理等，來獲得碘化鉛薄片，再將其轉換為鈣鈦礦薄片。利用此方法製作的碘化鉛薄片最薄可以到2.6nm，而後續本研究製作出轉換前碘化鉛薄片厚度為4nm的鈣鈦礦薄片電晶體。並確認鈣鈦礦薄片，如同其他研究，在室溫下呈現四方晶系。並且越薄的薄片，其出平面分子振動模式強度越低。而透過量測光致發光光譜，越薄的鈣鈦礦薄片的光致發光峰值會有藍移的現象，對應其具有越大的能隙。 後續，本研究將鈣鈦礦薄片製作成光偵測器與電晶體。對於光偵測器而言，越厚的鈣鈦礦薄片有越明顯的光電流變化，從光偵測器的電流開關比可以看到研究中最厚的薄片可以達到最薄的2.5倍，這是因為厚度較厚的鈣鈦礦薄片載子數量較多以及厚度足以吸收較多的入射光。而電晶體方面，較厚的薄片具有雙極性，較薄的薄片呈現P型。而厚度變薄遲滯現象變小、臨界電壓絕對量值變大的現象。

In this thesis, an experimental method to reduce the thickness of organic-inorganic hybrid perovskite flakes to several nanometers was proposed, and electrical and optoelectronic properties of perovskite nanoflakes were investigated. Different from the chemical vapor deposition method commonly used in the literatures, a solution method was adopted to obtain lead iodide flakes by adjusting the experimental conditions, such as: rotation speed, rotation time, whether to treat with an ozone cleaning machine, etc. After that, lead iodide flakes were converted into perovskite with solution method, too. The thinnest lead iodide flakes synthesized by this method can reach 2.6 nm. Perovskite flake transistors were subsequently fabricated. The perovskite flakes, like other researches, were tetragonal phase at room temperature. The thinner the flake, the weaker the out-of-plane vibrational mode. Blue shift, corresponding to a larger energy bandgap was observed in the photoluminescence peak as the perovskite flake becomes thinner. As the active layer of photodetectors, thicker perovskite flakes show more obvious changes in photocurrents. The on/off ratio of the photodetector with the thickest flake could reach 2.5 times of that of the thinnest counterpart. This is because the carrier concentration was larger and the flake was thick enough to absorb the incident light sufficiently. As the channel layer of the field-effect transistors, thicker flakes are bipolar and thinner flakes are p-type. Also, the thinner the flakes, the smaller the hysteresis phenomenon, and the larger the absolute value of threshold voltage.