| When the temperature of the detection target approaches room temperature,and itspeak radiation wavelength is in the long-wave range.And 8-14?m is an important atmospheric window.Therefore,developping of long-wave infrared focal plane detector is of great significance.However,the long-wave device has a narrow band gap,and one of the technical difficulties in preparing long-wave infrared focal plane lies in the high dark current of the long-wave detector.In As/Ga Sb type II superlattice is a periodic quantum structure material,which has the characteristics of flexible band adjustment,long Auger composite life,and large effective mass.Especially for long-wave band,the type II superlattice has good uniformity and is one of the preferred materials for preparing high-performance long-wave infrared focal planes.The main research content of this dissertation is to focus on the preparation technology and photoelectric performance of the InAs/GaSb ? superlattice long-wave infrared detector.The core goal is to reduce the dark current of the superlattice long-wave infrared detector and prepare a high-performance long-wave superlattice infrared focal plane detector.The main research contents and innovations are as follows:Firstly,film deposition technology related to the preparation of superlattice devices was systematically studied.The silicon nitride film was grown by using the Inductively Coupled Plasma Chemical Vapor Deposition?ICPCVD?technology.The performance of the film is related to the process parameters such as silane flow rate,ICP power and RF power.Among them,the RF power has an important influence on the stress of the silicon nitride deposited on the Ga Sb material.The RF power can make the compressive stress of the film reach 1000 MPa,which results the film to crack easily.The experiment finally obtained the optimized process of rapid deposition of silicon nitride,and applied to the mask growth of long-wave superlattice devices:Si H4 flow 45.0 sccm,N2 flow 38.0 sccm,ICP power 2000 W,chamber pressure 8.0 mtorr,temperature 75?,RF power 0 W.At the same time,an optimized process of low-rate silicon nitride film deposition was obtained and applied to the mesa passivation of long-wave superlattice devices:Si H4 flow 15.5 sccm,N2 flow12.5 sccm,ICP power 300 W,chamber pressure 8.5 mtorr,temperature 75?,RF power 0 W.The experiment also studied the deposition of silicon oxide film on Ga Sb material by ICPCVD.Unlike silicon nitride,the performance of silicon oxide is not related to various process parameters.Secondly,the etching processes of the superlattice device with a 50%cutoff wavelength 12.5?m were studied,and the relationship between the surface dark current and the Sb on sidewall surface was first proposed and verified.When device is wet etched by citric acid,the dark current density of the device is 3.8×10-3 A/cm2,and R0A is 37.2??cm2at 60 K.As the temperature decreases,the surface dark current will be the main part of the total current.The mechanism of surface dark current formation is that a disproportionation reaction between Sb2O3 and Ga Sb occurs on the sidewall surface of the mesa,and resulting a leakage channel of semimetal Sb on the surface.Dry etching using a Cl2/N2 inductively coupled plasma technology can obtain excellent electrical performance under the optimized etching conditions.Temperature is an important factor influencing the results of etching,as the temperature increases,the etching rate and etching selection ratio increase,the mesa tends to be right angle,and the dark current of the device also decreases.Within the scope of the experimental study,170?is the optimal etching temperature.At 60 K,the dark current density of the long-wave device etched at 170?is 1.9×10-4 A/cm2,R0A is89.1??cm2.Above 150 oC,the state of Sb from Ga Sb has changed very significantly,Ga Sb gradually disappears on the sidewall surface,and the dark current of the device decreases,indicating that Ga Sb on the mesa surface is related to the surface dark current.Finally,a 640×512 long-wave In As/Ga Sb type II superlattice infrared focal plane array was developed by the above basic processes.When the focal plane pixel is at 77K and the voltage is-0.05 V,the dark current is 2.7×10-9 A,and R0A is 19.0??cm2.At 60 K,the dark current of the pixel is reduced to 9.7×10-11 A,and R0A reaches838.4??cm2,indicating that the electrical performance of the pixel in the infrared focal plane with the silicon nitride passivation has been further improved.The focal plane array detector was flip-chip with the ROIC,and then loaded in a cryostat.The NETD of the focal plane array is 180 m K at 77 K,and the non-uniformity of the responsivity is 22%.At 60 K,the circuit injection efficiency will be higher than 90%.The bad pixel percent of the long-wave superlattice infrared focal plane array is0.95%,the non-uniformity of the responsivity is lower to 2.8%,D*is 6.61×1010cm?Hz1/2/W,NETD is as low as 17.2 m K. |
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