CVD直接成長之大面積MoS2/GaN異質接面自供能寬頻光偵測器

Abstract

本研究利用化學氣相沉積法的方式將二硫化鉬直接成長於氮化鎵基板上，此法能夠減少傳統機械剝離法及溼式轉印法在製程中容易產生的缺陷、材料厚度難以控制的問題，還能夠透過溫度、基板與材料源間的距離…等參數，調整成長後二硫化鉬的覆蓋率及大小。大面積二硫化鉬使我們可以利用更高製程效率的黃光微影取代電子束微影，成功製備出二硫化鉬/氮化鎵異質接面光偵測器。本研究對此二硫化鉬/氮化鎵光偵測器元件進行了光響應能力評估及分析，發現此元件具有自供能光偵測特性。在入射光波長404 nm，無外加偏壓時 (0V)，可得響應度為406 (mA/W)，偵測率為8.2×1011 (jones)，並且擁有良好的響應速度，上升/下降響應時間常數為18.6/74.9 ms (532nm, 0V)，以及對入射光功率密度良好的線性度，顯示了此元件優異的自供能光偵測能力。此外，利用二硫化鉬與氮化鎵結合能夠提升自近紅外光自紫外光波段的光吸收係數，使此元件在404、532、633、808 (nm)雷射量測下皆有良好的光響應，顯示了此元件寬頻偵測的能力。我們利用二維能帶模型對此二硫化鉬/氮化鎵異質接面結構之載子傳輸原理提出解釋。二硫化鉬/氮化鎵為第二型異質接面結構，透過光生伏打效應的概念，介面間的內建電場在無外加偏壓下能夠分離電子-電洞對產生光電流，使他能夠擁有自供能響應的特性。最後，我們針對了不同二硫化鉬分布密度進行光響應分析，得到擁有越高覆蓋率的二硫化鉬在無外加偏壓時有更高的響應度與偵測率，這吻合我們對於此材料是透過二硫化鉬與氮化鎵間的內建電場來形成自供能光偵測特性的推論。

In this work, the wafer-scale van der Waals epitaxial direct growth of Molybdenum disulfide (MoS2) on p-GaN/sapphire substrates using chemical vapor deposition (CVD) is demonstrated. The CVD method can avoid some of the issues often happen in conventional 2D materials transfer methods, such as interface defects, layer numbers control, or large-scale transfer. We fabricated MoS2/GaN heterostructure photodetectors by photolithography. The MoS2/GaN heterostructure photodetector shows self-powered and broadband photoresponse capability from near-infrared (NIR) to ultraviolet (UV). The high esponsivity of 406 (mA/W), a detectivity of 8.2×1011 (jones), is demonstrated at zero voltage bias under 404 nm laser. It also shows a fast response speed, the time constants of rising/decay are 18.5/74.9 ms (532nm, 0V bias), respectively. We provide a 2D band diagram to explain the carrier transport theory of the self-power properties. According to the Photovoltaic effect (PVE), the photo-generated carriers are split by the built-in voltage to detect without external bias.We also evaluate the photoresponse properties of different coverage MoS2. The higher coverage MoS2 device shows higher responsivity and detectivity without external bias. The results are consistent with our inference that PVE causes MoS2/GaN photodetectors' self-power capability.