| dc.description.abstract | 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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