| Summary: | 碩士 === 國立中央大學 === 照明與顯示科技研究所 === 103 === In this research, topic is Development of silicon-based epitaxial germanium films and photodetectors at a low temperature. Germanium whose bandgap is 0.66eV can absorb near-infrared light of wavelength. Germanium of Mobility is fast than silicon so germanium Integrated in silicon-based generally applies of high frequency device. Due to cutoff wavelength of Ge is at 1550 nm, so germanium can be used as a near-infrared photodetector. Ge films on Si is overcoming the large lattice mismatch (4.2% at 300 K), which cause a high threading dislocation density (TDD) in the Ge layers. Many Group in international use high temperature and annealing in fabrication to solve this problem. High temperature of fabrication will restrict to integrate in CMOS. In this research, all of the manufacture is low temperature(<375℃), advantage of which affect photodetector be integrated in COMS in the future.
We cooperated with NDL to operate Reduce Pressure chemical Vapor Deposition (RPCVD).The silicon-based epitaxial germanium Films were manufactured by RPCVD cooperated with NDL. The germanium films are part of 500nm and 2µm which are measured 183arsec and 119arsec by XPD. RMS of germanium films is 1nm by AFM and threading dislocation density is 〖10〗^7 〖cm〗^(-2)by EPD to be a high quality films. The photodetector is p-i-n structure whose way of p-doping are part of 1.ECR-CVD and 2. ion implantation. 1.The photodetector whose germanium films is 500nm by RPCVD are measured dark current density be 4.34 mA/cm^2(area is 530µm×530µm ) at -1V, responsivity is 0.32 A/W in 1310nm of laser and 0.24 A/W in 850nm of laser.
2.The photodetector whose germanium films is 2µm by RPCVD are measured dark current density be 1.86mA/cm^2(area is 530µm×530µm ) at -1V, responsivity is 0.1 A/W in 1310nm of laser and 0.05 A/W in 850nm of laser. Ion implantation of p-doped films possess high mobility and electric conductivity but we know concentration are not enough by SIMS.
In this experiment, all of photodetectors have low dark current density. This priority affect device have good signal-noise ratio. Dark current density is often a symptom of poor reliability.
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