Design and simulation of novel 2.05μm antimonide-based extended short-wave infrared (eSWIR) avalanche photodiode (APD)

GaSb-based avalanche photodiodes (APDs) operating in the extended short-wave infrared (eSWIR) require precise electric field partitioning to suppress tunneling in the narrow-bandgap absorber while enabling avalanche multiplication in the high-field multiplier. In this work, a simulation-based design study of Separate Absorption, Charge, and Multiplication (SACM) APDs operating near 2.05 μm is presented using Naval Research Laboratory (NRL) band parameters. Two transition implementations, step-transition and superlattice-transition, are investigated under matched electric field conditions, with charge-layer thickness systematically varied to evaluate its impact on electrostatic behavior. The results show that charge-layer thickness primarily determines the absorber electric field and the voltage margin between punch-through and avalanche breakdown. Thinner charge layers increase absorber field and expand the operating voltage window but reduce the efficiency of field confinement within the multiplication region, consistent with absorber-field-limited behavior. Conversely, thicker charge layers improve field confinement but reduce operating margin. The transition region influences the shape of the band profile and the resulting electric field distribution at the absorber–multiplier interface. Both implementations employ layered grading. However, the superlattice transition redistributes the band profile such that the most abrupt portion of the transition is alleviated. Under reverse bias, this produces a redistribution of the electric field, characterized by a local reduction in field upon entering the transition region before increasing to the breakdown field, whereas the step-transition design exhibits a monotonic increase. The results indicate that SACM APD design should be viewed as a two-scale electrostatic problem. The charge layer determines the global distribution of electric field across the absorber and multiplication regions, setting the overall operating window. In contrast, the transition architecture governs the local electric field profile at the absorber boundary, where tunneling is most sensitive. Because band-to-band tunneling depends exponentially on electric field, even small local variations in field near the heterointerface can dominate dark current. As a result, transition-region design provides a critical and previously underutilized degree of freedom for suppressing tunneling without sacrificing avalanche gain.