Basic Research On Si-based APD In Near-Infrared Communication Wavelengths

With the development of quantum communication,stable and efficient single-photon detectors for infrared communication wavelengths become a research focus.Many researchers have paid attention to the avalanche photodiode(APD)which is regarded as a potential photoelectric device for the detection of infrared light,even for the amplification of single-photon signals due to its internal carrier multiplication.Silicon(Si)is a perfect multiplication material due to its low ionization coefficient ratio(k value).Besides,Si is regarded as a suitable material for APD because of its low-cost and broad application.However,Si is not sensitive to the near-infrared light due to its large bandgap of 1.12 eV in room temperature.In order to take advantage of the merits of Si material,researchers have tried to combine Si with other material(Ge，InGaAs)to detect near-infrared waveband.This paper mainly focuses on how to realize absorption and detection of Si-based APD in near infrared waveband,and main works are summarized as follows:1.We simulate a traditional Ge/Si SACM APD and discuss the influence of structural parameters on performance.Meanwhile,we analyze the change of electric field distribution in this device and its mechanism.Besides,we design a potential structure of Ge/Si APD based on the oxide-free Ge/Si bonded interface.This lateral-collection Ge/Si APD can reduce the thickness of Ge layer because of its interesting electric field distribution,which combines specific lateral electric field(lateral carrier collection)with traditional vertical high electric field(vertical avalanche).This thin Ge layer structure can reduce the carrier transit time.Besides,earriers transport in this structure occurs at the mesa edge where high velocity region is created,also leading to the decrease of the earrier transit time.A high 3dB-BW of～20 GHz and low dark current(～10-12 A)of the optimized lateral-collection Ge/Si APD are achieved.2.Since the absorption of germanium at 1550 nm wavelength is less than 1310 nm,and its excess noise is too large.We also choose III-V group material as a absorption region for Si-based APD,simulating the heterojunction SACM(Separate Absorption,Charge,and Multiplication)APD with InGaAs material as absorption layer,Si material as multiplier layer and substrate material.The detection characteristics of these devices are analyzed.The InGaAs/Si APD fabricated by direct-bonding method can achieve a high gain of 103 and low dark current of 10-10A.The phenomenon of high switching ratio caused by the special conduction band potential well structure of InGaAs/Si heterojunction is found through simulation calculation.This phenomenon is helpful to realize the fabrication of high photocurrent output and high gain Si-based infrared APD devices.3.The bonding preparation of III-V/IV heterojunction material system was experimented by using a-Ge as the interlayer material.The effects of different interlayer thickness and annealing temperature on bonding quality were researched during the experiment.It was found that wafer bonding of more than 70%area could still be achieved in the case of the interlayer with the lowest film thickness of 4 nm,and a favorable PN junction electrical characteristic curve was obtained.