Research On Silicon UV Avalanche Photodetectors

High sensitive and low cost UV light photodetector is highly demanded because it is being widely applicated in the fields of scientific analysis,industrial systems,fire warning,quantum information technology and so on.In order to improve the spectral response of the silicon photodetector in the ultraviolet,this paper proposed to take advantage of the high gain of the avalanche photodetector in Geiger mode,and finally developed a highly sensitive UV silicon single-photon avalanche diode with the responsivity of 107A/W under the incident light of 200nm and the gain of 107 under the incident light of 261nm.The main research contents of this paper are as follows:1.In order to solve the problem that the absorption length of Si is only about 3-5nm at the wavelength of 200nm?280nm,the optical response of traditional silicon photodiodes used in visible image sensors is relatively low.Moreover,the high density of Si/SiO2 interface states makes the surface non-radiative recombination occur when the ultraviolet light passes through the interface states,which reduces the response of the ultraviolet light.Therefore,the structure of avalanche photodetector is proposed.The steep electric field distribution in the avalanche area causes the photogenerated carriers to be separated quickly and away from the surface.The characteristics of high gain of avalanche detector in Geiger mode are used to improve the spectral response of the detector in UV.In this paper,a coplanar silicon avalanche photodetector is fabricated based on pn junction.The test results show that the responsivity of the detector in Geiger mode reaches 2.97×107A/W at 200nm,and the frequency response at 850nm reaches 1.4GHz.It provides a new idea for the development of high sensitive silicon UV single photon detector.2.In order to reduce the non-radiative recombination of ultraviolet light in the high-concentration doped region,a cross finger structure is proposed.It can reduce the injection ratio in the high-concentration region of the device and increase the collection path of carrier by means of the ultraviolet light absorption in the low-doping region between the fingers.A coplanar cross finger avalanche photodetector is prepared.The test results show that in Geiger mode,the responsivity reaches 5.44×105A/W at 200nm.The reason of lower responsivity than the previous structure is that the electric field between fingers is lower and the carrier collection efficiency is low.The cross finger structure provides the possibility of reducing the non-radiative recombination in the high concentration region of the detector and improving the ultraviolet light response.3.In order to avoid the detector edge breakdown and further reduce the size of the device,a virtual protective ring is proposed.For this reason,two kinds of coplanar avalanche photodetectors were prepared,which used the virtual protective ring structure and the injection protective ring structure respectively to verify the effect of the virtual protective ring.The test results show that the test curves of the two protective ring structures are basically the same.The virtual guard ring structure provides a method to further reduce the device size,improve the duty cycle of the device and fabricate the array.