Research On Waveguide Integrated Germanium/silicon Avalanche Photodetector

Silicon photonic technology realizes the large-scale integration of photonic devices and optoelectronic devices by means of optical interconnection,it has been widely concerned in high-capacity application scenarios such as data centers and optical communication.As an important silicon photonics device,the high performance near-infrared detector is responsible for photoelectric signal conversion.?-? materials have no advantages in cost and heterogeneous integration with silicon materials,meanwhile,the epitaxial process of germanium is developing and can be compatible with CMOS process,thus germanium/silicon devices are more suitable to be prepared with silicon photonics platform to demonstrate low cost advantage.The avalanche photodetector has internal gain when it works,and it has small volume,high sensitivity and high responsivity.With the development of 100 G optical communication,near infrared APD has been paid more and more attention.In order to overcome the design contradiction between the bandwidth and optical responsivity of classic incident structure APD,the waveguide integrated structure appears and can be more conducive to the realization of on-chip integration.At present,waveguide integrated germanium/silicon avalanche photodetector has become one of the mainstream researches.In this paper,the waveguide integrated germanium/silicon APDs were studied.Based on the working mechanism of the avalanche photodetector,we found that for classic SACM structure germanium/silicon APDs the impurity concentration of charge layer has a great influence on the electric field distribution of device,thus accurate control of impurity distribution in charge layer during preparation will be a process difficulty.Lateral APD devices have simple structure and fabrication process,it can avoid the problem about charge layer mentioned above in design,and the main work of paper revolves around it.1.We explored the working mechanism of germanium/silicon lateral APD through TCAD tool and optimize its electric field distribution to improve the optical response characteristics by changing impurity doping,meanwhile qualitatively analysis towards the structural parameters of germanium region and gap was made to figure out their influences on the electric field and performances of devices,which has certain guiding significance for the structural design of germanium/silicon lateral APDs.2.The process flow of fabrication of waveguide integrated silicon/germanium lateral APDs was designed based on 8 inches silicon photonics platform of Institute of microelectronics,Chinese Academy of Sciences.Devices with different gap width were successfully prepared.The main process flows consist of etching process to prepare single mode waveguide and tapered waveguide,light etching to form focusing coupling grating,ion implantation on the substrate.Besides,RPCVD equipment was used to epitaxy high quality germanium films with the combination of the technique of selective epitaxy and low-temperature buffer layer,finally the electrode was formed after the contact hole and metallization process.3.The test results show that the attenuation coefficient of the single-mode waveguide is 2.58 dB /cm,the insertion loss and center wavelength of the grating is 3.08dB/port and 1552.1nm respectively.With reduction of 0.1?m for gap width,the absolute value of APD's breakdown voltage goes down about 5V,devices with gap width of 0.3 ?m have only-6.5 V of breakdown voltage,and the bandwidth of it can achieve as high as 20.06 GHz when measured under 90 percent of breakdown voltage;The breakdown voltage of device with gap width of 0.8?m is-28 V,under the condition that-37.6 dBm of effective incident light power was applied,it can obtain high responsivity of 75.89 A/W under the reverse bias voltage of-27.5 V.