A Multiscale Materials-to-Systems Modeling of Polycrystalline Pb-Salt Photodetectors

We present a physics based multiscale materials-to-systems model for polycrystalline $PbSe$ photodetectors that connects fundamental material properties to circuit level performance metrics. From experimentally observed film structures and electrical characterization, we first develop a bandstructure model that explains carrier-type inversion and large carrier lifetimes in sensitized films. The unique bandstructure of the photosensitive film causes separation of generated carriers with holes migrating to the inverted $PbSe|PbI_2$ interface, while electrons are trapped in the bulk of the film inter-grain regions. These flows together forms the 2-current theory of photoconduction that quantitatively captures the $I-V$ relationship in these films. To capture the effect of pixel scaling and minority carrier blocking, we develop a model for the metallic contacts with the detector films based on the relative workfunction differences. We also develop detailed models for various physical parameters such as mobility, lifetime, quantum efficiency, noise etc. that connect the detector performance metrics such as responsivity $\mathcal{R}$ and specific detectivity $\mathcal{D^*}$ intimately with material properties and operating conditions. A compact Verilog-A based SPICE model is developed which can be directly combined with advanced digital ROIC cell designs to simulate and optimize high performance FPAs which form a critical component in the rapidly expanding market of self-driven automotive, IoTs, security, and embedded applications.