二維材料與其體材料相比有著獨特且驚人的特性，例如：石墨稀的超高載子遷移率，因而成為近來熱門之研究領域。二維材料在光電元件應用上展現超越傳統半導體特性，少層p型硒化鎵於室溫下可視為直接能隙、少層n型硒化銦在6 nm以上為直接能隙，對光皆有著良好吸收率，因此本研究以GaSe、InSe凡得瓦垂直異質結構探討載子在界面的傳輸特性並進一步分析其光電轉換之特性與效率。經由測量電流對電壓關係(I-V特性曲線)，發現具有二極體整流特性之起始電壓0.2 V，並得到理想因子為1.7。由改變照光功率之測量，獲得典型光伏效應現象，在功率密度為10～4000 W/m^2之照光下，外部量子效應(External Quantum Efficiency, EQE)隨著照光功率增加而呈現下降之趨勢，0.03 %下降至0.006 %逐漸飽和，另外經由實驗數據證明了填充因子(Fill factor, FF)與轉換效率(Efficiency, η)在不同照光功率下呈現穩定值約0.38與5×10-4 %。我們進一部分析此異質結構之光電流轉換效率對應照光波長的關係，在改變照光波長500～800 nm之測量中(照光功率密度約2800 W/m^2)，約600 nm之光照為效率最佳的情況，且在照光為620 nm以上之波段，光電流明顯下降，顯示由於損失了GaSe被激發之激子(Exciton)所形成之光電流。最後，由改變施加閘極偏壓，利用閘極產生的電場改變材料中的主要載子濃度，得到P-N二極體之特性對應於閘極偏壓改變之結果，在負閘極偏壓下，二極體特性消失，正閘極偏壓下，二極體之理想因子最佳的量測值為1.4，出現於閘極偏壓為10 V，使二極體更接近理想I-V特性。而GaSe/InSe 異質結構的光電轉換效率沒有預期高的原因可能來自通道材料與SiO2介面之缺陷 ，使得載子遷移率低，造成光生電子電洞的複合率變高。經由改善接面品質，輔以本研究之測量結果，未來使GaSe與InSe能在太陽能電池中有更好的發展。

2D materials with a wealth of exotic dimensional-dependent properties are promising candidates for next-generation ultrathin and flexible optoelectronic devices. Indium selenide (InSe) and gallium selenide (GaSe), belonging to group-III monochalcogenides, are in the same crystal structure with similar lateral lattice constants (α_InSe = 4.002 Å, α_GaSe = 3.755 Å) and electronic structures. Pristine InSe and GaSe exhibit N-type and P-type transport behaviors, respectively, with carrier concentration of 1×10^15 and 1×10^14~4.5×10^15 m-3. In this study, we studied carrier transport properties in GaSe/InSe van der Waals heterostructure and further characterizes its optoelectronic properties. GaSe/InSe heterojunction exhibiteds rectification property with turn-on voltage at 0.2 V, and ideality factor n = 1.7. This junction also showed photovoltaic effect. Under power-dependence measurements, external quantum efficiency decreased from 0.03 % to 0.006 %, and become saturated. Fill factor and efficiency are stable with value 0.38 and 5×10^-4 %. Under wavelength-dependence measurements, it had the highest efficiency with wavelength ~600 nm; In addition, we observed ISC decreased rapidly when wavelength exceeded 620 nm. Finally, we performed Ids-Vds measurements under different back-gate voltages. The diode properties disappeared within negative back-gate voltages (-10 V to -80 V), however, the device approached more ideal I-V characteristic and got the best ideality factor of 1.4 under positive back-gate voltages at 10 V. Finally, such relatively low EQE of our device could be ascribed to the low mobility resulted from the trap sites in the interface of channel and SiO2 substrates. We expected optical-to-electrical conversion efficiency could be enhanced via improving the interface quality. It is anticipated that the fundamental understanding of charge transport properties at interface of GaSe/InSe is crucially important for future applications in optoelectronics.

論文審定書 i
誌謝 ii
摘要 iii
Abstract iv
目錄 vi
圖目錄 vii
第一章 序論 1
第一節 研究動機 1
第二節 前言 5
第三節 二維結構太陽能電池 8
第二章 儀器介紹 21
第一節 製程儀器 21
第二節 測量儀器 24
第三章 元件製程與元件結構 27
第一節 元件製程步驟 27
第二節 元件結構 30
第四章 實驗結果與討論 35
第一節 P-N二極體(Diode)特性 35
第二節 照光強度改變之ID-VD curve測量：Power dependence 37
第三節 照光波長改變之ID-VD curve測量：Wavelength dependence 42
第四節 不同閘極偏壓(Gate dependence)量測 46
第五章 總結 51
第六章 參考文獻 53

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