Simulations Of Electrical Performance For Open-Shell-Electrode Detector

Silicon detectors have advantages over other semiconductor detectors for their small volume,light weight,fast response speed,high sensitivity,high position resolution,high energy resolution,wide linear range,easy integration with readout electronics.They are widely used in high energy physics,astrophysics,space,medicine and many other fields.The main disadvantage of the relatively new 3D-Trench-Electrode silicon detector is that it has large dead space due to the fact that its trench electrode is not etched through.In this work,we propose a new type of 3D detector called the Open-Shell-Electrode Detector(OSED).The novel OSED can be etched through,thus removing the dead space from the detector.We correspond detactor electrical properties such as leakage current,capacitance,depletion voltage,charge collection,response time to the detector performance parameters such as noise,energy consumption,energy resolution,collection efficiency.Main research results of this article are:(1)The concept and design of the new OSED silicon detector are presented and described in detail.In cylindrical symmetry,the electric field distribution of a detector single cell with circular shape is the most uniform.In an array made of circular cells,we found that the gap region between cells is minimal when the electrode spacing is 22 μm.When the PN junction is at the out ring(the trench),the full depletion voltage is one-third of that when the PN junction at the central electrode.Therefore in our design and simulations,the PN junction is selected at the out ring.When designing the openings in the trench electrode,or as we called the open-shell-electrode,the value of the opening S is kept at0 S≤10 μm.Through these discussions,the structure of the OSED is determined.(2)In the Silvaco TCAD,our simulation toll,a device model for the novel circular OSED is established.The simulation adopts an OSED unit cell with a cylindrical structure.The open sell electrode is n+ with a doping concentration of 1019 Ph/cm3.The central electrode is p+ with a doping concentration of 1019 B/cm3.The detector bulk material is high resistivity P-type silicon with a doping concentration of 1012 B/cm3.After radiation to1×1016 n/cm2,the effective doping concentration is made as 1×1014 B/cm3 to simulate negative space charges induced by strong radiation.In the simulation process,the central electrode is the cathode,the outer trench is the anode.(3)Through the simulation,we made a 2D cut at z=151 μm to get 2D electric potential and electric field distributions of the detector.These distributions are uniform and there is no saddle point in electric potential distribution.The dead space of the OSED silicondetector is much smaller as compared to that of the conventional 3D-Trench-Electrode detector.Detector current-voltage(I-V)curves at different radiaiton fluences are obtained.Detector leakage current increases with radiation fluence.The SNR(Signal to Noise Ratio)is related to the value of the leakage current.For example,the leakage current is 5.87×10-9 A when there is no radiation,it increases to 6.28×10-8 A at a radiation fluence of 1×1015neq/cm2,and it further increases to 5.38x10-7 A at a radiation fluence of 1×1016 neq/cm2.As the opening S of the shell electrode increases,the detector leakage current slightly increases.At a surface charge concentration of 4×1011 cm-2 and a radiation fluence of 1×1016 neq/cm2,the breakdown voltage of the detector is 230 V.Detector capacitance-voltage(C-V)curves at different radiation fluences are also obtained.Capacitance-voltage(C-V)characteristic curves change with radiation fluence.However,the saturation capacitance has been found to be 122 fF,independent of radiation fluence.As the opening S of the shell electrode increases,the detector capacitance does not change significantly.The SNR(Signal to Noise Ratio)is related to the value of the capacitance as well.The full depletion voltage of the detector is 2V without radiation,it increases to 5 V at a radiation fluence of 1×1015 neq/cm2,and it further increases to 23 V at a radiation fluence of 1×1016 neq/cm2.Charge collection properties of the detector is slightly better near the opening regions of the shell electrode.However,as radiation fluence increases,Detector charge collection properties become worse in general.