Optimixation And Design Of Si-based Ge MSM Photodetectors

Owing to its excellent optoelectronic properties, which include high carrier mobility, narrow band gap, compatibility with silicon CMOS (complementary metal-oxide-semiconducto) circuits, germanium has been greatly used for silicon-based-light source and silicon-based-photodetectors. With the growing development of information society, high-dense monolithic integration will be one of the important persuit of silicon photonics. Silicon based germanium metal-semiconductor-metal photodetector can be used as high-speed detectors in optical systems for its easy fabrication, low capacitance, and sensitive to optical communication band (1.3-1.55μm).This thesis mainly focuses on the optimization of silicon based germanium metal-semicondctor-metal (MSM) photodetectors. The methods of dark current suppression, as well as further improvement of high-speed response were discussed in detail both theoretically and experimentally.From the aspect of dark current mechanism of MSM photodetectors, asymmetric interdigital electrodes and asymmetric area electrodes were introduced to the dark current suppression. The surctures of these two methods were simulated using ATLAS software. Then siliocon based germanium MSM photodetectors were fabricated and their optoelectronic performance were tested. Device structure influence on dark current was summarized. Through appropriate design of asymmetric structure, the dark current can be reduced to several μA, with the dark current density of4.47A/cm2, and the responsivity of our asymmetric devices can reach0.40A/W at wavelength of1550nm.In order to trade-off3dB bandwidth and responsivity, surface plasmon resonance effects were introduced to furtherly improve the optoelectronic performance of silicon based germanium photodetectors. By using finite difference time domain (FDTD) method, the device structure were simulated and optimised. The mechanism of surface plasmon resonance, together with the effect of the device structure on the performance of surface plasmon resonance were discussed in depth. Finally, the optimized structure of high performance photodetector was designed, of which the normalized spectral absorptioncan be as high as53.77%at the wavelength of1550nm with an enhancement factor of7.22.