The Structure Design And Research Of New Type APD Based On Silicon And Germanium

The explosive spread of the internet has increased the demand for highly sensitive optical detectors for high bit rate optical fiber communication systems. The avalanche photodiode (APD) is now finding acceptance in an increasing range of applications including optical communications, ranging, and laser systems. Its advantages lie in its small size,internal current gain, high-frequency response, and it usually requires a relatively low supply voltage. The materials used in APD structure have a major effect on determining the characteristics of the avalanche photodiode. There are three main materials that been used in avalanche photodiodes, germanium, silicon and group III-V compounds. Germanium can be used for wavelengths in the region 800 nm-1700 nm, and silicon can be used for wavelengths in the region between 200 nm - 1100 nm. Basic silicon photodiodes are very suitable for optical receivers because of their small capacitance and low dark current noise.However due to their absorption rate being limited by the silicon band gap, for silicon avalanche photodiode are normally restricted to use in the 800 nm to 900 nm range, and the germanium or other similar compound semiconductors are used in the 1300 nm to 1500 nm range.This paper based on the Silvaco TCAD semiconductor process simulation package. We build the SAM type APD device structure by Atlas module, and then simulate the basic photoelectric characteristics of the APD device. We have to adopt build impact ionization model, the carrier indirect composite model, the carrier mobility model and the light injection model. First of all, we simulated the relationship of avalanche breakdown voltage and device structure, observed the absorption efficiency of different wavelength photon in Si absorption area, and the influence of bias voltage on gian for Si absorption area in the device. Then,the light absorption area is replaced by Ge material, we simulated the absorption efficiency of Ge absorption area with different wavelength photon, as well as gain effect. Finally, we researched the characteristics of integrated Si/Ge avalanche photodiode device structure, and analyzed the impact of the Ge content in the SiGe layer on the leakage current. The influence of the capacitance characteristics is also discussed. In addition, we discuss the process flow of the improved avalanche photodiode device.