Fabrication And Characterization Of 4H-SiC Ultraviolet Single Photon Avalanche Photodiodes

Ultraviolet(UV)avalanche photodiodes(APDs)based on 4H-SiC have aroused great interest worldwide.Because this kind of device has the ability of detecting extremely weak or even single photon UV signals,which has many potential applications such as UV astronomy,corona detection,environmental monitoring,UV lidar,biological detection as well as jet engine or missile plume detection.Compared with traditional vacuum photodetectors,such as photomultiplier tubes(PMTs),SiC APDs have the advantages of being smaller in size,lower in cost,easier to be integrated and potentially have higher detection efficiency.Besides,semiconductor APDs normally have longer lifetime and can be operated at much lower voltage than that of PMTs.Meanwhile,compared with group-? nitrides,currently 4H-SiC semiconductor has considerably lower defect density,which is a key advantage for APD fabrication.As a result,most reported SiC APDs exhibit better performances in terms of dark current,avalanche gain and reliability.In this work,beveled mesa 4H-SiC ultraviolet(UV)avalanche photodiodes(APDs)with partial trench isolation are designed and fabricated;the device performances of APDs with device diameter ranging from 75?m to 1000?m are studied and 50-pixel 4H-SiC APD linear arrays capable of operating in Geiger mode are reported for the first time.The detailed results are shown as follows:1.A beveled mesa 4H-SiC ultraviolet(UV)avalanche photodiode(APD)with partial trench isolation is reported.By adopting partial trench isolation structure,when device diameter of the APD is 150?m,its fill-factor can increase from 33.9%to 63.5%compared with traditional full trench isolation structure.Photocurrent of the APD device shows corresponding increase when illuminated with the same UV light source.Through current-voltage,spectral response and single-photon detection characterizations,it is confirmed that the performances of the partial trench isolation APD do not degrade compared with traditional full trench isolation structure.The APD fabricated in our experiment with partial trench isolation shows a peak quantum efficiency of 66.4%at 270 nm and a single photon detection efficiency of 9.5%at 280 nm when the corresponding dark count rate is fixed at 1 Hz/?m2.2.APDs with different device diameters ranging from 75pm to 1000?m are fabricated,the current-voltage,spectral response and single photon detection characteristics of these devices are compared and the APD with 1000?m diameter still shows relatively high avalanche gain(>105)though its current-voltage characteristics suffers obvious degradation.3.A 50-pixel linear array of 4H-SiC ultraviolet avalanche photodiodes operating in Geiger mode is reported for the first time.The 50 pixels within the linear array are all capable of detecting single photons but with a small number of them suffering from extra leakage current near avalanche breakdown.The enhanced leakage is likely correlated with structural defects existing within the epi-structure,which would lead to higher dark count rate(DCR)at the same single photon detection efficiency(SPDE)in Geiger mode.For a low leakage APD device within the linear array,a room temperature SPDE of 9.7%at 280 nm is obtained with a corresponding DCR of 5.8 Hz/?m2.