Study On Ultraviolet Photodetector By Theoretical Simulation Design And Fabrication

China's marine satellite ultraviolet imaging instrument will use ?-N semiconductor photodetector for imaging,in order to fabric ultraviolet detectors with high responsivity,high detection rate,in this paper,we mainly study on the back-illuminated InGaN/GaN photodetector combined with the optical and electrical properties of InGaN semiconductor material.Inaddition,the problems in the study of the solar blind band Al GaN ultraviolet detectors and SAM-type APD devices are studied.The main research contents are as follows:First of all,the performance characterization parameters of the photodetector and the semiconductor device simulation platform Silvaco TCAD are introduced.The semiconductor basic equations and physical models applied in the numerical simulation are summarized.The effects of parameters such as the thickness of n-GaN,i-InGaN and p-GaN,the polarization effect and the minority carriers SRH lifetime on the spectral response of the device were specificly investigated in InGaN ultraviolet photodetector.The response spectrum of the simulation agrees well with the experimental test curve when the minority carrier SRH compound lifetime is 0.01-0.1 ns.The n-GaN affects the short-wave rejection ratio of the photodetector which has little effect on the peak responsivity.With the increasement of the thickness of i-InGaN layer,the responsivity of the photodetector will gradually increase and then reach the maximum value when the thickness of n-GaN and p-GaN keep consistent.The responsivity gets the peak value when the thickness of i-InGaN layer is 400 nm in this structure.The InGaN/GaN interface polarization charge density is small due to the low molar fraction of In,so that the polarization intensity has no significant effect on the detector responsivity.Inaddition,the influence of the thickness of the side surface passivation layer,the depth of etching damage,the width of the p electrode and the width of the mesa on the dark current of the InGaN/GaN hetero-junction photodetector were also numerically simulated.It is observed that the dark current increases with the thickness of the side surface passivation layer,and increases with the increase of the etching damage depth.And so on,the dark current of the photodetector increases with the width of the mesa,and there is no obvious relationship with the width of p electrode.When the thickness of the side passivation layer SiO₂ is 50 nm and the thickness of the etching damage is 20 nm,the simulation value of the dark current is in good agreement with the experimental test value.Then,the In_0.03Ga_0.97N/GaN hetero-junction photodetector was fabricated by standard ?-N mesa device preparation technology.The radius of the photosensitive surface was 30?m,the dynamic zero bias voltage was about 2.00×10¹²?,the quality factor R0A=5.66×107??cm²,the peak responsivity R=0.215A/W at 371 nm,the corresponding peak detection rate D*=2.34×10¹³cm?Hz1/2?W-1.Inaddition,the effects of n-electrode annealing conditions on the ohmic contact of p-electrode were studied in the fabrication process,and the dark current characteristics of the actual detector were also analyzed.When the samples were annealed in a nitrogen atmosphere,the shorter annealing time and the lower annealing temperature that the smaller the effect of the p-electrode ohmic contact,within a certain range,while ensuring that the n-electrode forms an ohmic contact.The research on the dark current of the real detector have the following results:?a?the reverse dark current decreases with the p-electrode width when the width of the mesa is constant,?b?the reverse dark current decreases with the width of mesa when the p-electrode width is constant,?c?the reverse dark current is smaller 3 orders of magnitude when the thicker electrode with the electrode lead wire.Finally,the response spectrum of the AlGaN ultraviolet photodetector was simulated when introduced with the tail effect optical model.The SAM structure APD device achieves the separation of the acceleration region and multiplication region when the thickness of n1 layer is 20 nm and the carrier concentration is 1.0×10¹⁸cm^-3.Inaddition,the early breakdown phenomenon of the SAM structure APD devices is studied.Here we have numerically simulated the electric field distribution in air with field structure,micro-mesa structure and oblique mesa structure.The intensity of the electric field at the edge of the p-electrode decreases and stabilizes with increase of the thickness of the passivation layer and the length of the field plate in a certain range.Adjusting the thickness of the passivation layer under the field plate and the length of the field plate can make the electric field intensity at the edge of the p electrode and the edge of the field board approximately equal,as a result,possibility of premature breakdown is minimized.Under the-100 V high reverse bias voltage,the 45 ° tilt angle of the inclined mesa area has a wide range with low electric field distribution.