本論文利用選擇性氧化複晶矽鍺柱/氮化矽/矽基材的結構來形成高品質之鍺量子點，以作為高效率的長波光吸收層，進而製備出可適用於850奈米到1570奈米波長的鍺量子點光電晶體。 藉由調變複晶矽鍺柱之尺寸與氧化條件，本文得以精準控制量子點大小及鑽入氮化矽與基板的深度，進而控制鍺量子點碰觸到矽基板後形成矽鍺殼之大小與厚度。鍺量子點及其下端矽鍺殼的大小，直接影響了鍺量子點光電晶體的吸光層厚度與提升載子移動之速度，透過以上特性，得以針對吸光波長之需求對元件進行最佳化之設計。 由於鍺量子點埋入氮化矽中會受到壓縮式應力，且隨著鍺量子點尺寸愈小，所承受的壓縮式形變愈大。藉此，我們可以調整掩埋在氮化矽中鍺量子點之大小，來調變鍺量子點所感受之壓縮式應力，並將其有效應用於N-type基板之鍺量子點光電晶體的閘堆疊層之中。 50奈米、90奈米鍺量子點成長於N-type基板之鍺量子點光電晶體，在850奈米波長光源(功率為 4.375mW)照射下，通道關閉區域其光電流與暗電流比值分別可達到 7.53×109 以及 3.69×109 倍，且響應度 (responsivity) 最高分別可達到 1605.58 A/W 以及 1483.32 A/W；90奈米鍺量子點成長於P-type基板之鍺量子點光電晶體，通道關閉區域其光電流與暗電流比值可達到 1.76×1010 倍，且響應度 (responsivity) 在最高可達到2996.33 A/W。吸光波長可達 1570 奈米，適用於光連結之應用。 ;In this thesis, we generated a high quality germanium quantum dots (Ge QDs) by selective oxidation of SiGe nano-pillar / Si3N4 / Si substrates as the light absorption layer with high efficiency at long wavelength , and manufactured the Ge QDs phototransistors that can apply to wavelength 850 nm to 1570nm illumination. By tuning the size of poly-SiGe piller and the oxidation environment, we are able to control the size of Ge QD and the depth that Ge QD migrates into the Si3N4 and Si substrate. Progressively, we can control the size and thickness of SiGe-shell, which forms as Ge QD “contact” with the Si substrate. The sizes of Ge QD and SiGe shell below Ge QD determine the thickness of light absorption layer of Ge QDs phototransistors and the increment on the mobility of carrier. Through the above properties, we can optimize and characterize transistor device according to needs of absorbing different wavelength illumination. When Ge QD embedded within Si3N4, it generates size-dependent compressive strains that the smaller Ge QD will suffer the higher strain. By tuning the size of Ge QD that embed in Si3N4, we are able to control the compressive stain suffered by Ge QD, and apply it to Ge QD phototransistor with N-type Si substrate. Under 4.375mW illumination at 850 nm, Ge QD phototransistors with 50nm and 90nm Ge QD formed on N-type Si substrate have the photo-current-to-dark current ratio with 7.53×109 / 3.69×109 tines and responsivity with 1605.58 / 1483.32 A/W；Under 4.375mW illumination at 850 nm, Ge QD phototransistor with 90nm Ge QD formed on P-type Si substrate has the photo-current-to-dark current ratio with 1.76×1010 tines and responsivity with 2996.33 A/W. The absorption wavelength can reach 1570nm that are appropriate to the optical interconnects.
