本論文利用選擇性氧化在氮化矽上方之複晶矽鍺柱的方式，形成鍺量子點包覆於二氧化矽內並鑽入下方氮化矽與矽基板接觸，並利用鍺量子點和矽基板接面生成3~4 nm品質良好的二氧化矽，同時解決矽鍺界面4.2%晶格不匹配與形成優良矽鍺異質結構，進而將此二氧化矽整合於金氧半(Metal-Oxide-Semiconductor )場效電晶體作為元件閘介電層，利用蝕刻鍺量子點上方的氧化層將之裸露，形成鍺量子點閘極/二氧化矽/矽底材之結構。藉此有效降低元件介電層厚度與電阻-電容時間延遲常數(RC delay time constant)，成功地研製出特性良好的鍺量子點閘極(Germanium quantum dot-gated)場效光電晶體(photoMOSFET)。
調變複晶矽鍺柱尺寸和氧化時間製作鍺量子點大小50 nm、70 nm和90 nm的鍺量子點閘極場效光電晶體。未照光時，電晶體有相當小的次臨限斜率，可做為開關元件使用。藉由光電量測得知，波長850 nm(功率4.38 mW)光照射下，鍺量子點大小50 nm、70 nm和90 nm的元件，光暗電流比值在元件關閉時分別為3.28×106、2.39×106和9.66×105；元件開啟時分別為8.23、11.3和5.13。光響應(Responsivity)在元件關閉時分別為5.25 A/W、6.26 A/W和6.6 A/W；元件開啟時分別為1481 A/W、2913 A/W和10597 A/W，元件對近紅外光的響應度相當出色。
最後，探討調變鍺量子點尺寸對元件特性的影響，不照光情況下，尺寸較小的量子點有較好的次臨限斜率與訊號放大能力。照光情況下，鍺量子點尺寸由小至大其鍺含量由少至多，光電流量和光響應在元件關閉時因鍺含量增加而提升；元件開啟時受到元件自身的訊號放大能力影響，鍺量子點尺寸較小的元件具有較大的光電流量和光響應，補足尺寸小量子點激發光電流較低的缺失。

In this thesis, Germanium quantum dots (Ge QDs) which individually surrounded SiO2 were formed by using selective oxidation of poly-crystalline SiGe pillars over the Si3N4 layer on the Si-substrate and then Ge QDs would burrowed into Si3N4 and eventually touched Si-substrate. The high quality SiO2 of 3-4 nm in thickness between Ge-QD and Si, which solves 4.2% lattice mismatch in between QD and Si-substrate, can be employed as the dielectric layer in metal-oxide-semiconductor field effect transistor. As the top SiO2 was etched until Ge QDs exposed, Ge-QD/SiO2/Si-substrate MOS structure was fabricated. Accordingly Germanium quantum dot-gated photoMOSFET which possessed tremendous photo-electrical characteristics was then realized, etching the gate dielectric thickness leads to effective reduction on RC delay time constant.
Phototransistor with Ge QDs of 50 nm, 70 nm and 90 nm were fabricated, respectively, by the SiGe pillar size and time oxidation. The transistor had small subthreshold swing at darkness can be considered as a switch. Under illumination with wavelength of 850 nm and incident power of 4.38 mW, current enhancement of devices with Ge-QDs of 50 nm, 70 nm and 90 nm is 3.28×106, 2.39×106 , and 9.66×105 in off region and 8.23, 11.3, and 5.13 in on region respectively. Responsivity is 5.25 A/W, 6.26 A/W, and 6.6 A/W in off region and 1481 A/W, 2913 A/W, and 10597 A/W in on region were also observed showing great performance for near infrared ray.
In the end, we investigated the effect of the QD size. The device with smaller QD size would get better subthreshold swing and amplification without illumination. Under illumination, photo current and responsivity would increase with higher Ge content because of larger Ge-QD in off region. However, the device with small QD size was determined by its amplified ability and then compensated the effect of small QD size for less Ge content, getting better photo current and responsivity.

[1] https://en.wikipedia.org/wiki/Moore’s_law
[2] W. C. Dash et al., “Intrinsic optical absorption in single-crystal germanium and silicon at 77℃ and 300℃,” Physical Review, 99, 1151 (1955)
[3] J. E. Roth et al., “Optical modulator on Si employing Ge quantum wells,” Frontiersin Optics., 93, 191112 (2007)
[4] D. Ahn et al., “High performance, waveguide integrated Ge photodetectors,” Opt.Exp., 15, 3916 (2007)
[5] S. J. Koester et al., “Germanium on SOI infrared detectors for integrated photonic applications,” IEEE J. Sel. Topics Quantum Electron., 12, 1489 (2006)
[6] Roosevelt people, “Physics and application of GexSi1-x/Si strained-layer heterostructures,” IEEE Journal of Quantum Electronics, 22, 1696 (1986)
[7] F. K. LeGoues et al., “Anomalous strain relaxation in SiGe thin films and superlattices,” Physical review letters, 66, 2903 (1991)
[8] T. K. P. Luong et al., “Control of tensile strain and interdiffusion in Ge/Si(001) epilayers grown by molecular-beam epitaxy,” Physical review letters, 114, 83504 (2013)
[9] D. J. Eaglesham et al., “Dislocation-free Stranski-Krastanow growth of Ge onSi(100),” Physical review letters, 64, 1943 (1990)
[10] H.Kroemer, “Theory of a Wide-Gap Emitter for Transistors,” Proceedings of the IRE, 45, 1535 (1957)
[11] K.-W. Ang et al. “Low-voltage and high-responsivity germanium bipolar phototransistor for optical detections in the near-infrared regime,” IEEE Electron. Device Lett., 29, 1124 (2008)

[12] Y. Kang et al., “Monolithic germanium/silicon avalanche photodiodes with 340 GHz gain-bandwidth product,” Nat. Photon., 3, 59 (2009)
[13] S. Assefa et al., “Reinventing Germanium avalanche photodetector for nanophotonic on-chip optical interconnects,” Nature, 464, 80 (2010)
[14] J. Wang et al., “Silicon waveguide integrated germanium JFET photodetector with improved speed performance,” IEEE Photon. Technol. Lett., 23, 765 (2011)
[15] A. K. Okyay et al. “SiGe optoelectronic metal-oxide semiconductor field-effect transistor,” Opt Lett., 32, 2022 (2007)
[16] A. K. Okyay et al., “Silicon germanium CMOS optoelectronic switching device: Bringing light to latch,” IEEE Trans. Electron. Devices, 54, 3252 (2007)
[17] Ryan W. Going et al., “Germanium gate photoMOSFET integrated to silicon photonics,” IEEE Journal of Selected Topics in Quantum Electronics, 20, 4 (2014)
[18] T. Akatsu et al. “Germanium-on-insulator (GeOI) substrates—A novel engineered substrate for future high performance devices,” Proc.Mater. Sci. Semicond. Process., 9, 444 (2006)
[19] C. J. Tracy et al., “Germanium-on-insulator substrates by wafer bonding,” J. Electron. Mater., 33, 886 (2004)
[20] J. H. Nam et al., “Germanium on insulator (GOI) structure using hetero-epitaxial lateral overgrowth on silicon,” ECS Trans., 45, 203 (2012)
[21] Y. Liu, M. Deal, and J. Plummer, “Rapid melt growth of Germanium crystals with self-alignedmicrocrucibles on Si substrates,” J. Electrochem. Soc., 152, 688 (2005)