本論文利用調控預先定義好之複晶矽鍺柱之鍺含量、幾何圖形大小，以及熱氧化時間，來精準控制鍺量子點的直徑大小、位置及鑽入矽材的深度，以達成量身訂作鍺量子點/矽異質結構之功效。經由高解析度穿隧式電子顯微鏡與能量散佈光譜儀觀察分析鍺量子點與矽的異質界面確認此法可以精準地置放鍺量子點在矽底材上，而且藉由矽與鍺之間約3–4 nm的二氧化矽來化解矽與鍺之間4.2 %晶格不匹配的問題。利用此鍺量子點/矽異質結構，本文成功地製備出高品質的鍺近紅外光偵測器與光電晶體。 將50 nm 鍺量子點陣列整合於金屬-氧化物-半導體 (MOS) 二極體的閘極堆疊層中可以有效地提升在可見光至近紅外光的光電轉換效率與光響應。分別在400–1000 nm、1160、1500 nm光源照射下，鍺量子點金氧半二極體所展現之光電流與暗電流比值可高達35,000、1,800與87倍，且具有非常低之暗電流 (1.1 A/cm2)。在近紅外線光照射下，鍺量子點/矽界面所累積之正電荷造成內建電場的產生，有利於元件操作速度的提升。螢光光激發譜線也證實此50 nm量子點的光激發峰值約在 0.9 eV (約在1380 nm)，由強度相依的螢光譜線解晰可知此1380 nm的螢光譜線是來自於導/價電帶之間激子之交互作用，另由溫度解析的螢光譜線強度可萃取出其活化能量約10.72 meV。 最後將 50 nm鍺量子點陣列整合於金氧半光電晶體中，能夠在 850 nm 的光源照射下展現清楚的光調變能力。汲極的光飽和電流與暗電流之比值增益可以達到 310 %。本文所呈現之鍺量子點光偵測元件之製作完全與現行之互補式金氧半電晶體技術相容，所提供之高品質鍺/矽異質結構與光元件有利於積體電路中光連結的應用。 In this thesis, we have successfully demonstrated Ge quantum dots (QDs) of desired size, location and depth of penetration into the Si substrate using the control available through nano-patterning and selective oxidation of SiGe pillars over a buffer layer of Si3N4 deposited over the Si substrate. Transmission electron microscopy (TEM) and electron dispersive x-ray spectroscopy (EDX) analyses reveal that a 3–4 nm thin amorphous interfacial oxide is present between the Ge QD and the Si substrate, successfully improving the crystalline quality of the Ge QD by de-coupling the lattice-mismatching constraint of 4.2%. A low dark current of 1.1μA/cm2 and a high photocurrent-to-dark current ratio of 35,000 and 1,800, and 87 respectively, under 1.5 mW illumination at the wavelength of 400-1000, 1160, and 1500 nm were measured on MOS photodiodes based on the 50-nm-GeQD/Si structures. Notably the photocurrent almost becomes saturated at zero bias, revealing a strong built-in E-field within the QD that would enhance the operating speed of Ge QD photodetectors. The corresponding photoluminescence (PL) peak of 50-nm-Ge QD centered at 0.9eV with a fitted α of 0.96 from the power dependent PL spectra suggest the PL emission being dominated by exciton recombination in the Ge QDs. The activation energy (Ea) extracted from temperature dependent PL is about 10.72 meV. Finally, we incorporated a 50-nm-Ge QD-array into a phototransistor (W/L=10 m/10 m) and demonstrated a large ratio of photo drain current to dark current up to 310% under 850-nm illumination. The demonstrated high-performance Ge QD MOS photodetector was realized in a CMOS compatible approach, offering a great potential for future Si-based optical interconnection applications.
