Design And Fabracation Of 4H-SiC Sam-APD Ultraviolate Photodetectors

With the advantages of high quantum efficiency,high response speed,and high UV-visible ratio,the junction-based solar-blind UV detector based on third-generation semiconductor materials such as SiC and GaN has broad application prospects in the military and civilian fields.The avalanche UV detector employs an avalanche multiplication effect to amplify the optical signal and increase the responsivity.In the Geiger mode,it can accurately detect extremely low-ultraviolet light signals.In this paper,a 4H-SiC sam-APD structure UV detector with absorption layer separated from the multiplication layer is studied.The design idea of this structure is to increase the thickness of the absorption region,increase the quantum efficiency,and make the multiplication of photogenerated carriers arise in the thin multiplication region to obtain a uniform gain.At present,research on avalanche ultraviolet detectors at home and abroad has made a lot of progress,and domestic avalanche detectors based on 4H-SiC materials have not yet been widely commercialized.Edge breakdown,large dark current,and non-uniform internal gain have become important factors limiting device performance.This article from the perspective of the principle and simulation,combined with experiments,discussed the vertical structure of the device and the lateral edge of the terminal device performance,proposed some of the devices to improve the performance of the program,the specific work includes:1.The modulation effect of the vertical structure of the device on its internal electric field and breakdown voltage was analyzed.A simplified formula for the distribution of the electric field inside the device at various doping concentrations and thicknesses of multilayer pn junction structures was deduced,and a design idea for the vertical structure was proposed.From the design point of view,the longitudinal structure of several devices was designed.After the simulation,it was verified that the electric field in the multiplication layer could reach 4 MV/cm before the breakdown of the device,and the electric field in the absorption layer was 1 MV/cm,which satisfied the high gain of the multiplication layer.The absorption layer also has a higher drift speed.2.Through the simulation,the feasibility of the inclined mesa terminal,the MJTE terminal,and the JTE injection type terminalcorresponding tothe variationof the vertical design was studied,as well as the fringe electric field.The simulations found that the small-angle negative slope terminal is suitable for the case where the concentration difference between adjacent two layers is large,the positive slope terminal is suitable for the case where the concentration difference between two adjacent layers is small?less than4 times?,the MJTE terminal depends on the the doping concentration of the heavily doped side and requires that the doping concentration on the heavily doped side should not be greater than 2×10¹⁸ cm^-3,and for the JTE injection type termination with a multiplication layer doping concentration of 4×10¹⁷ cm^-3,the ion implantation concentration should be within the range of 1×10¹⁸ cm^-3 to 1.5×10¹⁸ cm^-3 to achieve a good edge breakdown suppression.Considering the cost and ease of implementation,two kinds of sam-APD structures with positive and negative mesa are designed.3.In the simulation,the effect of the surface etching window on the quantum efficiency and the influence of the window on the electric field below are analyzed.During the experiment process,the etching of the window should be avoided to affect the lower electric field.Based on the principle of a low electric field well below the window,a sam-APD structure design scheme for separating the lateral absorption region and the multiplication region was proposed.4.A sam-APD device was actually fabricated.The peak responsivity of the tested device was 0.15 A/W,and it was located near the 260 nm wavelength,corresponding to a quantum efficiency of 71.5%.the applied voltage was from 5 V to 126 V,and the peak responsivity was from 0.013 A/W.Change to 673.18 A/W.The breakdown voltage of the device is 127 V,the dark current is on the order of 10^-9 A,the dark current is 89 nA at 95%breakdown voltage,and the gain is close to 100.Through contrast experiments,it was found that the passivation of SiO₂ by the method of PECVD at the edge of the mesa reduces the dark current by 1² orders of magnitude.According to the results,it is presumed that the dark current of the device is determined by the edge leakage of the mesa at low voltage.At high voltage,the edge trap captures a single charge,which causes the edge electric field to increase,leading a local avalanche,and the dark current increases.Using thermal oxidation can further improve the edge quality and reduce dark current.