Impact of Band Anticrossing on Band-to-Band Tunneling in Highly Mismatched Semiconductor Alloys

Abstract

We theoretically analyze band-to-band tunneling (BTBT) in highly mismatched, narrow-gap dilute nitride and bismide alloys, and quantify the impact of the $\mathrm{N}$- or $\mathrm{Bi}$-induced perturbation of the band structure---due to band anticrossing (BAC) with localized impurity states---on the electric-field-dependent BTBT generation rate. For this class of semiconductors, the assumptions underpinning the widely employed Kane model of BTBT break down, due to strong band-edge nonparabolicity resulting from BAC interactions. Via numerical calculations based on the Wentzel-Kramers-Brillouin approximation we demonstrate that BAC leads, at fixed band gap, to reduced (increased) BTBT current at low (high) applied electric field compared to that in a conventional ${\mathrm{In}\mathrm{As}}_{1\ensuremath{-}x}{\mathrm{Sb}}_{x}$ alloy. Our analysis reveals that BTBT in ${\mathrm{In}\mathrm{N}}_{x}{\mathrm{As}}_{1\ensuremath{-}x}$ and ${\mathrm{In}\mathrm{As}}_{1\ensuremath{-}x}{\mathrm{Bi}}_{x}$ is governed by a field-dependent competition between the impact of $\mathrm{N}$ ($\mathrm{Bi}$) incorporation on (i) the dispersion of the evanescent Bloch band linking the valence and conduction band edges, which dominates at low field strengths, and (ii) the conduction- (valence-) band-edge density of states, which dominates at high field strengths. The implications of our results for applications in long-wavelength avalanche photodiodes (APDs) and tunneling field-effect transistors (TFETs) are discussed. For APDs, we describe that leakage currents in ideal dilute nitride and bismide devices are likely comparable to those in devices based on conventional III-V materials, but that the expected reduction of the hole impact ionization rate in ${\mathrm{In}\mathrm{As}}_{1\ensuremath{-}x}{\mathrm{Bi}}_{x}$ is promising from the perspective of obtaining low excess noise factor. For TFETs, we describe that $\mathrm{Bi}$ incorporation provides the potential to obtain both reduced subthreshold swing and increased on-state current, making ${\mathrm{In}\mathrm{As}}_{1\ensuremath{-}x}{\mathrm{Bi}}_{x}$ of interest for the development of low-power, high-speed devices.