Design And Fabrication Of An Entirely Group ? PIN Photodetector With Broad And Flat Response

In order to meet faster and larger capacity information transmission,optical communication technology has developed rapidly since the 21st century.Therefore,it is particularly important to develop a broadband photodetector that can completely cover all communication bands included 850 nm,1310 nm,and 1550 nm.Group ?semiconductor materials include Si,SiGe,Ge,and GeSn,etc.They show good characteristics in the preparation of photodetectors,and are compatible with Si-based processes,suitable for large-scale production,and have good commercial prospects.However,it is difficult for a device made of single group ? material to meet the needs of broadband detection.Therefore,combining the excellent characteristics of these materials,theoretically designing a structure with excellent performance,and experimentally exploring the device preparation process should be a challenging work nowadays.This thesis focuses on the theoretical design and experimental preparation of the entirely group ? PIN photodetector with a broad and flat response.The main research content and conclusions are the following three aspects:1.We simulate the spectral response and dark current density of PIN photodetectors with active regions of Si,SiGe,Ge and GeSn materials respectively.We analyze the different degree of red shift of the absorption peak position as the thickness of the active region increases.Combining the characteristics of Si-based epitaxial growth and the absorption characteristics of these four materials,we designed a broadband photodetector covering alll communication bands.By optimizing the device structure and adjusting the layer thickness of the active region,a flat optical response is obtained within the range of 700 to 1800 nm,the responsivity is maintained at about 0.57 A/W.The dark current density is reduced to 0.17 mA/cm2.This is beneficial to reduce the noise signal in the detection system and improve signal-to-noise ratio.2.We prepare a Ge film on the ultra-high vacuum vapor deposition system by using a low-temperature Ge buffer layer.We promoted the interdiffusion of Si and Ge materials through high-temperature annealing,and successfully obtained SiGe materials with a Ge composition from 0 to 1 with a dislocation density of about 7 ×107 cm-2.According to the experimental data and theoretical calculation,the diffusion of Si and Ge elements at high temperature is simulated.This provides a reference for the subsequent experimental process.Combined with ozone treatment,the second epitaxy was performed on the SiGe virtual substrate to obtain a high-quality Ge film with a FWHM of 248 arcsec.The surface morphology of the epitaxial layer was optimized by mechanical polishing,and the RMS was as low as 0.36 nm.3.A SiGe PIN photodetector was prepared by selecting SiGe materials that meet the design requirements.The ?-? characteristics,optical and dark currents of the detector were characterized,and was compared and discussed in combination with simulation work.The normalized photocurrent of the detector reaches a peak near 800 nm,and meets a high value in the wavelength range of 600 to 900 nm.This is in good agreement with the simulation results.