Research On The Photoresponse Enhancement Of Silicon Based Photodetector

As a common material for semiconductor photodetectors,silicon has an indirect band gap structure and electron multiplication as the main material characteristics,which makes silicon-based avalanche photodiode（Si-APD）have the advantages of high gain coefficient,low noise and good stability.It has been widely used in the detection of visible and near-infrared bands.In recent years,with the rapid development of visible light communication（VLC）technology,there is a more urgent need for high-sensitivity detectors in the visible light band.Si-APD has attracted more and more attention because of its excellent performance.However,the general Si-APD has low responsivity in the blue band,which limits its application in VLC systems.In addition,due to the short response cut-off wavelength of Si-APD,which is only 1.1μm,its application in the field of near-infrared wide-spectrum detection is also severely limited.In order to improve the spectral responsivity of Si-APD in blue light band and expand its response spectrum,this thesis has carried out relevant research work and achieved the following main research results:（1）A kind of high blue light spectral responsivity Si-APD basic epitaxial structure was designed and optimized.By pre-posing the absorption layer,postposing the field control layer and the multiplication layer,and optimizing the parameters of each functional layer,the optical responsivity of the device in the blue band is improved.The calculation results show that when the bias voltage V_apd was 0.95V_br-apd,the optical responsivity in the blue band of 400～500nm was 3.72～6.08A·W^-1.（2）The nanohole array structure for enhancing the blue light absorption of Si-APD was designed and fabricated.The test results showed that the blue light band achieves an optical absorptivity of more than 0.91 and an average optical absorption gain of 0.63 under normal incidence.When the incident light angle is greater than 60°,the optical absorptivity in the blue light band still exceeded 0.73.Under the same applied bias voltage(V_apd=148V),compared with the Si-APD without the nanohole structure,the photocurrent of the device at 400nm,450nm and 500nm increased by more than 120%.（3）A composite nanohole array（DCN-A）structure was designed to enhance the light absorption of silicon thin film devices in the visible light band by using the light capture effect of DCN-A.The calculation results showed that when the silicon film thickness was 3μm,the optical absorptivity exceeded 0.8 in the wavelength range of 400～678nm.（4）A basic epitaxial structure of Si/Ge-APD with wide spectrum and high response was designed and optimized.By pre-posing the Si multiplication layer and the field control layer and postposing the Ge absorption layer,and optimizing the parameters of each functional layer,the high responsivity of the device in a wide spectral range is achieved.The calculation results showed,that the device could achieve a wide spectral response of 0.4～1.6μm,when the bias voltage is V_apd=0.95V_br-apd.The peak response wavelength is 1.30μm and the optical responsivity is 11.2 A·W^-1.（5）A back reflection grating structure for near infrared light absorption enhancement was designed.Compared with devices without back reflection grating structure,at 1.31μm the light absorptivity increased from 0.35 to 0.69,and the light absorption gain is about 0.97;at 1.55μm,the light absorptivity increased from 0.17 to 0.58,and the light absorption gain is about 2.41.When the bias voltage was V_apd=0.95V_br-apd,the photoresponsivity at 1.31μm increased from 11.1A·W^-1 to 15.4A·W^-1,and the responsivity at 1.55μm increased from 1.7A·W^-1 to 5.47A·W^-1.