Design and analytical modeling of high-performance mid-wavelength infrared photodetectors: an nBn architecture

Due to the instability of the conventional Hg_1-xCd_xTe alloy, the demand for barrier-based superlattice device structures for next-generation infrared photodetectors is rapidly growing. InAs_1-xSb_x, a Ga-free III–V ternary alloy, has the potential to show an advancement in the development of fourth-generation mid-wavelength infrared detectors. In this work, we develop an analytical, reliable simulation model to predict the dark current behavior of an nBn photodetector at various conditions and explain the physics of this new device structure to understand the operation of back-illuminated nBn photodetectors quantitatively. To provide the best possible performance, we consider InAs_1-xSb_x ternary alloy to design the absorber region due to its band gap tunability with Sb molar composition and favorable absorption characteristics. In order to complete the device design, InAsSb is used as a contact layer, and a lattice-matched, large-bandgap barrier layer of AlInAsSb is employed with the intent of minimizing diffusion current, depletion-region Shockley-Read-Hall (SRH) generation and leakage current in such devices. To construct the band structure of the considered heterostructure, we first determine the hole quasi-Fermi-level outside of the thermal equilibrium by solving the coupled equations for the electrostatic, carriers' current continuity, and Poisson equations. Finally, we calculate the current-voltage characteristics to gain insight into the dominant mechanisms in the generation of dark current and demonstrate how the radiative and non-radiative processes affect the performance in relation to temperature and applied bias. In addition, we shed light on the performance of the considered photodetector by varying the depth of the contact and absorber regions. Our findings from the current device design show that the InAsSb/AlInAsSb-based nBn architecture may be a promising alternative for achieving high performance using a simplified device structure while circumventing issues related to the conventional material system, thereby serving as a basis for next-generation infrared detectors.