Design And Fabrication Of Si-based Ge Photodetector

Si-based Ge materials have been extensively applied in the field of Si-based opto-electronic integration and microeletronic devices due to their advantageous properties. Si-based Ge PIN photodetector has attracted much attention for its possible application in Si-based photonic integrated ciruits. The long diffusion time of minority carrier in the n-or p-type Ge, high Schottky barrier height and large contact resistance in metal/Ge contacts due to the strong Fermi-level pinning effect have been therotically predicted to affect the performance of Ge photodetectors. Therefore, the research on optimal design of photodetector and reduction of the specific contact resistivity of metal/semiconductor becomes the most important topics in fabricatoin of Ge devices.In this thesis, we calculated the3-dB cut-off frequency of the photodetector based on the continuity equations to optimize the parameters. Some key technologies of Si-based Ge photodetector have been investigated for higher performance of Ge photodectors. The main works are summarized as follows:1. The3-dB cut-off frequency of the photodetector are calculated based on the continuity equation. The influence of the thickness of p-Ge、 n-Ge and i-Ge on3-dB cutoff frequency of the photodetectors are investigated. The sturctures of the Si-based photodetectors are designed and optimized.2. The specific contact reistivities of metal/Ge contacts are extracted with circular transmission line model. The results show that the specific contact resistivity of Al/p-Ge is1.84x106Ω.cm2and the value of NiGe/Ge is1.43x1O-5Ω.cm2. in addition, Al/n+Si contact is also fabricated with the specific contact resistivity of5.21x10-5Ω.cm2. These values are helpful to achieve high performance Ge photodetectors.3. Relatively high quality Ge materials for PIN photodetectors are epitaxially grown on Si and SOI substrates. It is shown that the dark current of Ge photodetecotor on Si substrate is lx10-7A at reverse bias of-IV, wihc is lower by about one order of magnitude than that on SOI substrate. The photo-responsivity is about0.25A/W for both of the photodetectors on Si or SOI substates. The3db bandwidth of the photodetector on SOI substrate with24μm mesa diameter is about7.5GHz, which is larger than4GHz for the photodetector on Si substrate. The performance limitation of the photodetectors should be attributed to the longer diffusion time of minority carriers in n-or p-type Ge and the crystalline quality.