摘要
SiC雪崩光电二极管(APD)是用于探测微弱紫外光的优选器件。通过研究器件在高压下的光响应行为,发现随着偏压的增加,器件响应峰值和截止波长始终稳定在280 nm和380 nm处,表明SiC APD在雪崩击穿状态下仍具有可见光盲特性。这说明SiC APD在进行微弱紫外光探测时,凭借材料本身性质便可屏蔽可见及红外光的影响,有利于降低器件复杂度和成本。另外,为了增大器件的感光面积,将SiC APD直径增大到500μm,器件在95%击穿电压下,暗电流仅为2×10^(-10)A,当暗计数为1 Hz/μm^(2)时,器件单光子探测效率为0.7%,实现了SiC APD尺寸上的突破。
Objective High-sensitivity ultraviolet(UV)detectors are required in many critical applications such as corona discharge,m issile plume detection,environmental monitoring,and non-line-of-sight communications.As an attractive candidate for weak UV signal detection,avalanche photodiodes(APDs)operating in Geiger mode exhibit promising performance,including small size,low dark current,and high multiplication gain.Wide-bandgap semiconductor materials,such as Ga N and Si C,can effectively shield the influence of visible light and infrared light,showing obvious advantages in the field of UV detection.The defect density of Ga Nis relatively high,which leads to a generally high dark current in Ga NAPDs.In addition,the photoresponse behavior of Ga NAPDs under high pressure undergoes a significant red shift,and the cut-off wavelength is extended to 440 nm,indicating the loss of visible light blindness.In comparison,Si Ccan construct APDs with a much lower dark current than Ga Nowin g to its excellent material epitaxial technology.However,there is still little research on the high-voltage photoresponse characteristics of Si CAPDs,which are a key issue related to the background noise of the device.This work discusses the photoresponse behavior of Si CAPD under high voltages.Moreover,owing to material defects,the size of the Si CAPD is always below 300μm,but a device with a large photosensitive area is needed to improve the detection sensitivity.Although some studies have reported Si CAPDs with a diameter of 800μm,the key parameter of the single-photon detection efficiency has not been successfully detected.In this study,low-dark-current Si C APDs with a diameter of 500μm were successfully fabricated,and the devices exhibited single-photon detection performance.This is clearly a breakthrough in terms of the size of Si CAPDs.Methods Si CAPDs were fabricated on n-type 4H-Si Csubstrates(Fig.1).The epi-structure from bottom to top consists o f a 10μm p+layer(NA=3×1018cm^(-3)),a 0.78μm n-multiplication layer(ND=1×1015cm^(-3)),a 0.2μm n layer(ND=1×1018cm^(-3)),and a 0.15μm n+contact layer(ND=1×10^(19)cm^(-3)).To suppress peak electrical field around d evice edge,the beveled mesa with a slope angle of 5°was obtained via photoresist reflow technique,and the mesa was etched down to the multiplication layer by inductively coupled plasma.The device surface was then passivated by thermal oxidation at 1050℃in oxygen atmosphere followed by a 1μm Si O2layer deposited by plasma enhanced chemical vapor deposition at 350℃.The n and p type metal stacks,both based on Ni/Ti/Al/Au(35 nm/50 nm/100 nm/100 nm),were deposited by electron-beam evaporation.The devices were then annealed at 850℃for 3 min in N2ambient by rapid thermal annealing.Results and Discussions To analyze whether the Si CAPDs still have visible light blindness in the Geiger mode,the photores ponse characteristics of the Si CAPD are measured under high voltages.The results show that the response peak of Si CAPD is always maintained at 280 nm when the voltage changes from 0%to 90%breakdown voltage(Fig.3).It is proved that Si CAPDs still exhibit visible-li ght blindness characteristics under high voltages.Owing to the properties of Si C,Si CAPD enables the shielding effect of visible and infrared light,which greatly reduces the complexity,volume,and cost of the device.The activation energy of the 500μm Si CAPD is 0.131 e V(Fig.5),which indicates that the tunneling effect is the main cause of the dark current.At present,the best Si Ce pitaxy technology can grow epitaxial wafers with a dislocation density of 1000--2000 cm-2.This implies that there are at least 2--4 dislocations in Si CAPD with a diameter of 500μm,which exacerbates defect-assisted tunneling and leads to a rapid increase in dark current.Therefore,the material defect density is a key problem that restricts the development of large-sized Si CAPD.The dark current of the reported Si CAPDs at 95%breakdown voltage has been calculated,and the comparison shows that the 500μm Si CAPDs f abricated in this work have a lower dark current(Fig.7).Most importantly,the 500μm Si CAPDs in this work still have the single-photon detection capability.At a dark count rate of 1 Hz/μm^(2),the single photon detection efficiency of the device is 0.7%.The most recently reported largest diameter of Si CAPD with single-photon detection capability was 300μm.Although the single-photon detection efficiency of the 500μm Si CAPD reported in this work needs to be improved,a breakthrough in device size has been achieved.Conclusions In this work,by studying the photoresponse characteristics of Si CAPDs under high voltages,it is proved t hat Si CAPDs still exhibit visible light blindness in the avalanche breakdown state,which is more suitable for weak UV light detection than traditional Si or Ga N.In addition,we successfully achieve a breakthrough in the photosensitive area of Si CAPD and fabricate a large-sized Si CAPD with single-photon detection performance.The dark current of the device is better than the existing level.However,to further improve the single-photon detection efficiency of large-sized Si C APDs,it is necessary to optimize the quality of Si Ce pitaxial wafers in future work.
作者
杨成东
苏琳琳
夏开鹏
马文烨
Yang Chengdong;Su Linlin;Xia Kaipeng;Ma Wenye(School of Electronic Information Engineering,Wuxi University,Wuxi 214105,Jiangsu,China)
出处
《中国激光》
EI
CAS
CSCD
北大核心
2022年第24期15-19,共5页
Chinese Journal of Lasers
基金
国家自然科学基金(62106111)
无锡学院引进人才科研启动项目(2021r011,2021r012)。
