本篇論文探討以傳統互補式金氧半電晶體（ complementary metal-oxidesemiconductor, CMOS）製程所製作之鍺量子點光二極體（photodiodes）、光電晶體（phototransistors）及其元件物理/電氣特性。主要具體的成果有三：第一、成功開發出以熱氧化介電層上的複晶矽鍺（poly-Si0.87Ge0.13）方法來形成鍺量子點；且其對於可見光至紫外光有高吸收效率。第二、實作出閘介電層含量子點的MOS光二極體，並分析不同量子點層數（零、一及三層）對於電流－電壓（current-voltage,I-V）特性的影響及電子/電洞在其內的傳輸機制。利用變溫I-V 分析來探討暗電流機制，並論證percolation hopping 理論為主要傳輸機制。在照光下，鍺量子點光二極體的電流大幅增加且展現具放大效應的光響應（amplified responsivity）； 亦即鍺量子點層從零、一增至三層時，光響應（及對應的量子效率）分別從4.64（1.42%）、482（148%）增至812 mA/W（245%）。此外，波長-光響應圖也顯示當量子點縮小（9 nm → 5 nm）後光譜峰值有明顯的藍移現象，意謂著吸收光的機制可能源自於鍺量子點的量子侷限效應。第三，實作並論證雙閘式薄膜電晶體（thin-film transistors）結構的鍺量子點光電晶體。相較於不照光而言，此鍺量子點光電晶體在光波長405－450 nm 照射下，有顯著的電流增加且次臨限特性得以明顯改善。這意謂著只有光激發的電洞透過垂直電場注入通道並貢獻於光電流，而無光激發電子所引發的接面位障下降的副作用。鍺量子點光電晶體的波長-光響應圖與光二極體之結果相吻合，表示光電晶體的光吸收亦源自量子點的量子侷限效應。變溫及光暫態量測顯示此光電晶體有良好熱穩定性及光吸收效率。未來此等鍺量子點光偵測元件預期將可與矽電子元件整合至矽基板以作為光電積體電路。 This thesis investigates the device physics and electrical characteristics of Ge-QD photodiodes (PDs) and hototransistors (PTs) fabricated in a complementary metal-oxide-semiconductor (CMOS) process. The main features encompass as follows. First, thermally oxidizing poly-Si0.87Ge0.13 onto a dielectric layer produces Ge QDs embedded in an SiO2 matrix to serve as an efficient absorption layer for visible to ultraviolet light. Secondly, we have successfully demonstrated the feasibility of MOS PDs including multi-layer Ge QDs in the gate oxide and elucidated the current–voltage characteristics in terms of zero, one and three Ge-QD layers. Ge-QD PDs exhibit dramatically enhanced current under light illumination in the inversion mode and amplified responsivity (quantum efficiency) from 4.64 (1.42%), through 482 (148%) to 812 (245%) mA/W, respectively, as the Ge-QD layer number increases from zero, through one to three. Shrinking Ge QD size from 9.1 nm to 5.1 nm reveals considerable blueshift in spectral peak energies, originating from the quantum confinement effect (QCE). The temperature and bias dependences on the dark current ascribe the charge transport mechanism to be percolation hopping. Thirdly, Ge-QD PTs are realized by double-gated thin-film transistors with Ge QDs in the top-gate dielectrics. Compared with the current in darkness, 405-450 nm light illumination strongly enhances drain current and improves the PTs’subthreshold characteristics, following from that only photo-excited holes within Ge QDs inject into the active channel via vertical electric field and contribute to photocurrent without the counterpart photo-generated electron-induced junction barrier lowering. Spectral responses of Ge-QD PTs are consistent with that of Ge-QD PDs, attributing the PTs’photo-absorption to QCE. Temperature-dependent and light pulse characterizations demonstrate Ge-QD PTs have great thermal stability and photo-absorption efficiency. These Ge-QD PDs and PTs offer a deterministic approach to integrate with Si-based electronics monolithically.
