本論文主題為多層鍺量子點之製備及其在光偵測器上的應用。在高溫退火矽鍺氧合金時，矽會被優先氧化而鍺原子會自氧化物中被釋放出來並埋藏在氧化物與氮氧化矽介面，利用此選擇性氧化可製備出奈米尺寸的鍺量子點，且量子點的尺寸決定於鍺量子點釋放與聚集的機制，我們先利用電漿助長化學氣相沉積系統沉積非晶矽鍺氧/非晶氮氧化矽多層膜，並進行高溫退火處理，以形成包埋於氧化層內的多層鍺量子點。實驗結果顯示對非晶矽鍺氧/非晶氮化矽多層膜進行高溫退火處理後，可得到多層、分佈均勻且尺寸約為2~8奈米的鍺量子點，鍺量子點的結晶性係藉由拉曼光譜量測結果推知。增加非晶氮氧化矽層厚度，可以有效改善各層鍺量子點密度的均勻性。
接著將埋有多層鍺量子點的氧化層製作成金-氧-半MOS結構的光偵測器元件，首先藉由觀察到電容-電壓(C-V)特性的磁滯現象可判斷量子點生成情形及電荷儲存效果，所得到的記憶窗口可達3.39伏特。當埋有多層鍺量子點的氧化層厚度提升時，可有效降低元件暗電流，而得到較高的光/暗電流比值。
當鍺量子點密度較高時，可得到較高的光電流及較好的光響應度，且響應頻譜峰值波長會藍移。另外，在微弱的光訊號下(0.02 mW)，鍺量子點密度較高及氧化層厚度較薄的元件可以有效偵測到微弱(0.02 mW)的光訊號。外加偏壓較大或是元件氧化層厚度較薄時，由於較大電場會使光生載子的漂移速度變快而提升元件的響應速度。元件的RC時間常數也對上升下降時間有很大的影響，時間常數越大則上升下降時間會越長，響應頻寬也會越小。

In this thesis, multilayer Ge quantum-dots (QDs) have been fabricated and applied to photodetectors. Since the Si will be preferentially oxidized during the high-temperature annealing of SiGeO alloy and the segregated Ge atom will pile-up along the SiO2/SiON interface, it could be expected that the Ge quantum-dots could be tentatively formed with the Ge atom segregation and agglomeration. The QDs’ size depend on annealing process conditions, including temperature, ambient, and duration. The multilayer a-SiGeO/a-SiON thin-films have been prepared with a plasma-enhanced chemical vapor deposition system, then with a thermal annealing for a-SiGeO/a-SiON thin-films, the multilayer, well-separated, and 2~8 nm-sized Ge QDs were obtained. The crystallinity of Ge quantum-dots has been checked with a Raman spectroscopy. Increasing the thickness of a-SiON was beneficial to the formation of upper Ge QD layer, and a more uniform density of multilayer Ge QDs was obtained.
The metal-oxide-semiconductor (MOS) photodetector (PD) structures with multilayer Ge QDs embedded in oxide have been fabricated. From the obtained C-V hysteresis phenomena, the formation of Ge QDs and their charge storage effects were investigated. The obtainable memory window for MOS structure with multilayer Ge quantum-dots was 3.39 V.
Increasing the oxide thickness was effective to decrease the PD dark current and obtained a higher ratio of hotocurrent to dark current of PD.
A higher density of Ge QDs resulted in a higher photo-current, a better photo responsivity, and a blue-shift of peak response wavelength. Moreover, the amplified responsivity of PDs also can be seen in the spectra. The PD with a higher density of Ge QDs and a thinner oxide thickness could be used to detect the weak (0.02 mW) incident light effectively. By applying a large bias voltage or using a thinner oxide, the larger electric-field in the PD would increase the drift velocity of photo-generated carriers, and the response speed of PD became faster. The effect of device RC constant to rise-time and fall-time was significant. A large RC constant brought about the longer rise-time and fall-time and smaller response bandwidth.

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