氮化矽波導整合鍺量子點光電晶體之研製及分析

Abstract

本論文將一步驟氧化形成鍺量子點/二氧化矽/矽鍺之異質結構製作於金氧半場效電晶體之通道區。利用SOI基板本身之Buried oxide作為披覆層，氮化矽二維錐形波導作為核心層提供對接耦合（Butt couple）的媒介；閘極金屬選用可透光之氧化銦錫作為電極。以乾蝕刻調控閘氧化層厚度至38.5 nm及3.5 nm，並以鍺量子點及矽鍺作為光吸收材料，製作出可供垂直入射及側向入射量測之光電晶體。 閘氧化層厚度3.5 nm元件在未照光下，常溫所量測之次臨限斜率為80 mV/decade，元件開關電流比值達到3.41×108 A/A，顯示極佳的閘極調控能力。當元件關閉時，以功率約1.9 mW，波長850 nm、1310 nm及1550 nm光垂直入射下，分別得到108、300及30 A/A之光增益；當元件開啟時，以功率約0.1 μW，波長850 nm、1310 nm及1550 nm光垂直入射下，光響應度分別為139.4、2.23及6.81 A/W。顯示元件在近紅外光波段具有優異的光偵測特性。端面研磨後進行閘氧化層厚度38.5 nm元件之側向照光量測，在功率143 μW，波長850 nm側向入射光下，有15.3倍的光增益。波導整合的光偵測元件將使光連結系統的更加容易及可行。

In this thesis, we fabricated a heterostructure of Ge Quantum Dots/SiO2/SiGe in the channel of a MOSFET in a single oxidation step. Applying the buried oxide layer of SOI substrate and the 2-D tapered Si3N4 waveguide as the cladding and core layer for butt-coupling, respectively. For normal incidence optimal transmission, we chose ITO as the gate electrode. In other words, we demonstrated a waveguided phototransistor which can be measured either by normal incidence or lateral incidence, the absorption layer consists of Ge QDs and SiGe shell . We controlled the gate oxide thickness of 38.5 nm and 3.5 nm by means of dry etching. In the darkness, good switching behavior (subthreshold swing of 80 mV/decade), and high on/off ratio (Ion/Ioff = 3.41×108 A/A) were measured on the phototransistor with tox=3.5 nm at 300K. At off state, photocurrent gains are 108, 300, and 30 A/A under a normal incidence power of about 1.9 mW at 850 nm, 1310 nm, and 1550 nm, respectively. At on state, photoresponsivities are 139.4, 2.23, 6.81 A/W under a normal incidence power of about 0.1 μW at 850 nm, 1310 nm, and 1550 nm, respectively. Indicating that the phototransistor has a significant photodetection in the near-infrared regime. After the edge polishing, photocurrent gain value of 15.3 A/A under a lateral incidence power of 143 μW at 850 nm are measured on the phototransistor with tox=38.5 nm. The waveguided phototransistor would provide a better access to Si optical interconnect and make the integration more feasible.