The Research On Leakage Current Of Silicon Driff Detector Based On Surface Passivation Technology

As a high-performance X-ray detector,silicon drift detectors have extensive and important applications in various fields such as aerospace,nuclear industry,medical treatment,and security inspection.With the vigorous development of these industries in China,the demand for silicon drift detectors is also increasing.However,the technological monopoly of the detector abroad has greatly restricted the development of related industries in China,so it is urgent to start independent research of silicon drift detector production technology.In the production of silicon drift detectors,surface passivation is a very critical process,which plays a decisive role in the performance of the device.The quality of the surface passivation directly determines the surface leakage current,and the surface leakage current accounts for a large part of the total leakage current of the detector.Therefore,reducing the surface leakage current through good surface passivation is very important for improving the performance of SDD.This article mainly aims at solving the problem of excessive surface leakage current due to surface state caused by surface pollution and damage during the process.By adopting a new surface passivation structure,the device surface is well passivated.Finally,the surface state density is so small that it can lay a solid foundation for the production of high-performance silicon drift detectors.Based on the silicon surface passivation theory,two new passivation structures are proposed in this paper.The main work is explained as following:(1)Based on the excellent passivation characteristics of SiO2 and Al2O3 film,two composite passivation structures are proposed,both of which are SiO2/Al2O3/SiO2 composite layers.The difference between the two structures is that the growth method of silicon oxide on the surface of the silicon substrate is different.One is growth using plasma enhanced chemical vapor deposition(PECVD)technology,and the other is growth through nitric acid oxidation of silicon(NAOS).In the experiment,the effects and reasons of different passivation structures and process conditions on the minority carrier lifetime were explored.It is found that the passivation effect of the composite dielectric layer is much higher than that of the single-layer dielectric film,and annealing can significantly improve the surface passivation.Under the condition of light injection carrier concentration of 5e15 cm-3,the final minority carrier lifetime of the silicon substrate passivated by SiO2(PECVD)/Al2O3/SiO2 stacks is 1767 ?s.Silicon substrates passivated by SiO2(NAOS)/Al2O3/SiO2 structure have a final minority carrier lifetime of 5224 ?s,which is much higher than other passivation structures.(2)In order to further study the working principle of the device and the impact of some passivation effects on the device leakage current,this article establishes the device leakage structure model through Sentaurus software,and explores the influences of surface recombination rate,substrate quality,silicon substrate and charge at the interface of Si on the leakage current of SDD.(3)SiO2(NAOS)/Al2O3/SiO2 passivation layers were applied to the passivation of SDD.The test found that the leakage current of the device has dropped to the lever of 5 nA/cm2 at normal temperature.And in the follow-up experiment,by cooling the device to minus 40?,we successfully detected the X-rays emitted by the Fe55 source with an energy resolution of 210 eV@5.9keV.