SiGe Waveguide Resonant-cavity-enhanced Photodetector

Resonant-cavity-enhanced (RCE) photodetectors and waveguide photodetectors have been proposed for achieving high speed and quantum efficiency. The former leads to the decoupling of quantum efficiency and speed successfully, but there is trade-off between the responsivity and the line width of spectra, and the absorption length is limited by the critical thickness of SiGe. The latter resolves the interdependence between response speed and quantum efficiency as the directions of incident light and current are orthogonal and also can be easily applied to optoelectronic integration.We propose a novel SiGe waveguide-RCE photodetector for visible to near infrared operation. The novel device owns the merits of waveguide and waveguide-RCE photodetector. Contrasting to the conventional waveguide photodetetors, the device area can be designed small enough to satisfy high - speed operation. Contrasting to the RCE photodetectors, the limitation of SiGe critical thickness is circumvented and clever design can be expected. The following studies were carried out in the present thesis:(1) The influence of parameters on the performance including quantum efficiency, wavelength selectivity and response speed of waveguide-RCE photodetectors is studied in details. The parameters such as reflectivity of the front and rear mirrors, absorption length are optimized to obtain high quantum efficiency. The simulation by the method of transmission matrix predicts that high quantum efficiency up to 82% can be obtained for the photodetectors with 1nm line width. An optimization procedure for designing RCE photodetectors is proposed. Simultaneously, the main factors for determining the response speed are analyzed.(2) Based on electromagnetic theory of dielectric waveguide, 3D distribution of the field is simulated by BPM of SiGe/Si MQW waveguide. The coupling efficiency between fiber and waveguide is analyzed.(3) The processes and the key technologies for fabricating SiGe photodetectors were studied. The condition related to photolithography and various parameters of ICP are groped to form small waveguide and lateral reflectors with smooth side - wall. Waveguide photodetector and waveguide-RCE photodetector have been successfully fabricated.(4) Electrical performance and spectral response of the device are measured. Relatively small dark current has been obtained for both types of the photodetectors. Within a certain range, the intensity of photocurrent increases with increasing absorption length of waveguide photodetectors, and the spectral response peak wavelength is about 1008 nm.