Study On Dark Current Optimization Of T2SL Longwave Detector

Not so long ago,the InAs/GaSb type Ⅱ superlattice material has been used as the main material of infrared detectors.The heterojunction formed by the InAs/GaSb type Ⅱ superlattice is a broken gap band alignment.After absorbing perpendicularly incident infrared radiation,the electrons in InAs and the holes in GaSb can tunnel to achieve inter-band transition.The conduction band in microstrip is formed by the overlap of electron wave function,and the valence band in microstrip is formed by the overlap of hole wave function.By changing the InAs/GaSb type Ⅱ superlattice’s ratio of the layer thickness and the number of cycles,the equivalent performance band range can be continuously changed within 0.2 eV,which can realize long-wave infrared detection.However,the larger dark current density has become an important factor that limits the improvement of the optical detection performance of the type Ⅱ superlattice long-wave infrared detectors.Therefore,it is of scientific significance to study the dark current of long-wave detectors.In this paper,four barrier-type long-wave detector energy band structures of pBp,nBn,pπMn,and CBIRD are designed by simulation of the flexible material structure design characteristics of the superlattice.The purpose is to suppress the dark current of the detector,and the pBp structure is aimed at the dark current characteristics are analyzed and optimized.The main research work in this paper is as follows:(1)Using the Luttinger-Kohn model based on the 8×8 k·p theory,the energy band structure diagrams is included the absorber layer,barrier layer or contact layer which in different structures are calculated,and some parameters in absorber layer are calculated using Fermi’s golden rule,such as cut-off wavelength and peak light absorption coefficient of the superlattice.(2)Using the Poisson equation and the current continuity equation,the relationship between the dark current and the bias voltage of four type Ⅱsuperlattice long-wave detectors under low and high temperature conditions is calculated.At the same time,the dark current density of the four detector structures was compared and analyzed.The result shows that under low temperature conditions,due to the existence of the barrier layer,the dark current under low bias voltage is main consist of diffusion current,and under high bias voltage the dark current is main consist of tunneling current;while under high temperature conditions,direct tunneling current in the dark current is always the largest.(3)The dark current of pBp detector is optimized,and the influence of different doping concentration and layer thickness on the dark current of pBp detector is studied.The calculation results show that the dark current density of the optimized doping concentration and layer thickness of the pBp detector is 2.2×10-5 A/cm2 which is a decrease of the dark current density before the optimization.Order of magnitude,providing direction and ideas for the optimization of dark current for the type II superlattice long-wave detector.