High-performance InAs/GaSb Ⅱ Superlattice Midwave Infrared Photodetectors

As the core optoelectronic conversion devices of infrared detection systems,infrared photodetectors have been widely used in various applications such as night vision,military missile tracking,medical imaging,and remote sensing,and are developing towards improving the imaging capability,pixel density,and operating temperature of detectors.Motivated by the tunable bandgap,high absorption and quantum efficiency,low Auger recombination rate and tunneling current,as well as the good fabrication compatibility with standard CMOS platform,InAs/GaSb type-Ⅱ superlattice（SL）detectors have demonstrated excellent performance in infrared regions and are currently one of the most promising infrared materials for room temperature detection.However,the relatively high noise and short carrier lifetime greatly limit the further performance improvement of InAs/GaSb detectors.To address these issues above,a stepped structure is proposed by energy band engineering and applied to the absorber layer of InAs/GaSb detector with nBn design.The nBn structure can suppress dark currents significantly,and a built-in electric field is introduced by the stepped absorber,which promotes the transport and collection efficiency of photo-generated carriers,the device with a stepped absorber exhibits high detection performance in the mid-wave infrared（MWIR）region.The research contents and results are as follows:（1）The subband structures and absorption spectra of InAs/GaSb SL are calculated by 8×8 k·p model,and the relationship between SL period and parameters such as effective bandgap,miniband position,carrier effective mass and absorption coefficient is investigated.Benefiting from the flexible tuning of energy band structure of SL,three InAs/GaSb SL with different periods,similar bandgaps,and simultaneous offsets in the conduction and valence minibands are designed by the energy band engineering,which can form a newly stepped structure.（2）The performance of InAs/GaSb SL MWIR detector with a stepped absorber is analysed and discussed comprehensively.Due to the enhanced photo-generated carrier transport,the device with a stepped absorber exhibits a maximum quantum efficiency of46.0%at 150 K;Owing to the low dark current density of 3.9×10^-3 A/cm² and high maximum responsivity of 1.81 A/W,the maximum specific detectivity of the device with a stepped absorber reaches 4.26×10¹⁰ cm·Hz^1/2/W at 4.9μm,which is 52.7%higher than the device with a uniform absorber;Meanwhile,the maximum specific detectivity of the device with a stepped absorber remains 1.16×10¹⁰ cm·Hz^1/2/W at 170 K,demonstrating the potential of high temperature operation.Furthermore,as the built-in electric field can partly alleviate the limitation of short carrier lifetime and diffusion length in InAs/GaSb SL,the maximum specific detectivity of device with a stepped absorber can be further increased to 5.08×10¹⁰ cm·Hz^1/2/W at 150 K by optimizing the structure of stepped absorber,which provides a feasible method to obtain high-performance InAs/GaSb SL infrared detectors.