Design And Simulation Of Sb-based Superlattice Very-Long-Wavelength Infrared Detector

Infrared detectors are of vital importance and extensive applications in civilian and military field,including: security,night imaging,missile warning and guiding,meteorological and hydrological detection,etc.With the continuous advancement of material technology and energy band structure design concepts,infrared detectors have achieved rapid and impressive progress towards high detection rates,high resolution,high operating temperature,miniaturization and multicolor detection.However,with the increasing demand,the commercial MCT detectors are facing many problems such as large area array manufacturing difficulties,high cost and poor stability and uniformity.At the same time,many new infrared focal plane materials of highperformance have emerged,among which antimonide-based In As / Ga Sb Type-II superlattice material stands out,being a candidate material for next generation infrared detector.In As / Ga Sb superlattice has the valuable merits of convenient energy band adjustment,good uniformity,Auger suppression,and high effective carrier mass,rendering its superiority especially in long and very-long wavelength region.The most outstanding advantage of Type-II superlattice materials is that they can freely adjust the energy band structure of the material,by varying the thickness or composition of the material within the superlattice period.In this work,a superlattice infrared detector simulation system has been established,including three components: superlattice band structure calculation,device band edge simulation and dark current simulation.The system is calibrated through analysis and fitting of experimental data.A general simulation procedure for an infrared detector is briefed:(1)determine the detection demand of the device;(2)use the 8 band k·p method based on Nextnano software to calculate superlattice band structure,and figure out the appropriate superlattice periods for each region that meet the need of band-matching;(3)use mathematical software to perform dark current simulation and find the dominating dark current mechanism;(4)using the device band edge simulation tool to reproduce operating condition and optimize device structure including doping and thickness;Last,list the growth plan,test and verify whether if it works.Facing the problem of too high dark current in our present VLW detector,we performed simulation and analyzed the device structure.It is found that the problem directly originates from the tunneling dark current caused by the high doping concentration of the barrier region.It leads to the serious band bending inside absorber and too close distance between conducting and valence band.After optimizing superlattice periods inside absorber and barrier,we propose a new barrier VLW detector design also based on the P?MN structure: Thin Barrier P?BN structure.On the one hand,the structure adopts P-type doping inside barrier and forms a P-P junction with absorber,in order to eliminate G-R and tunneling current.On the other hand,the barrier layer of structure is shortened around 150 nm to ensure maximum carrier transport.We cut down the barrier layer thickness based on our detailed research on the relationship between barrier thickness and carrier transport ability.The results show that a proper thin-barrier would bring both high QE and high RA.Afterwards,we further increase doping concentration inside barrier to reduce minority carrier amount and thus suppressing diffusion current.According to our simulation,the structure has the dark current characteristic of "Flat"(Diffusion)—— "Ascending"(G-R)——“Boost”(Tunneling)as verse bias increases.QE of above 45%,operating bias of-50 m V,dark current of 7.7x10-4 A/cm2 and specific detectivity of 1x1011 cm Hz1/2/W are expected.Next,we have proposed another structure design: Multi-Section Doping pBp structure based on.Its barrier layer is divided into three parts,the left and righ part are P-type doped to suppress G-R and tunneling current,while the middle part is N-type doped to elevate carrier transport.It will achieve the same performance with thin barrier P?BN structure.Moreover,we proposed a passivation method: First,perform additional shallow etching through M-barrier towards the top of absorber;Then cover a dielectric passivation layer with fixed charge on the device surface.The fixed charge will generate strong electric field and affect the energy band at the surface layer,turning the electron accumulation layer into electron depletion,thus cutting down the surface leakage channel inside absorber.Last,we analyzed three Long-Wavelength detectors based on Thin Barrier P?BN structure,and found the ideal diffusion dark current plateau at low bias,which verifies the effectiveness of new structure.Also,we concluded that current passivation method is not stable and uniform enough for mass production.