Transient Phenomena in Sub-Bandgap Impact Ionization in Si n-i-p-i-n Diode.

Sub-bandgap (SBG) impact ionization (II) enables steep subthreshold slope that enable devices to overcome the thermal limit of 60 mV/decade. This phenomenon at low voltage enables various applications in logic, memory, and neuromorphic engineering. Recently, we have demonstrated sub-0.2-V II in n-i-p-i-n diode experimentally primarily based on steady-state analysis. In this paper, we present the detailed experimental transient behavior of SBG-II in n-i-p-i-n. The SBG-II generated holes are stored in the p-well. First, we extract the leakage mechanism from the p-well to show two mechanisms: 1) recombination–generation and 2) over the barrier (OTB), where OTB dominates when barrier height ${\phi }_{b}<\textsf {0.59}~\textsf {eV}$. Second, we analytically extract the SBG-II current (${I}_{\textsf {II}}$) at 300 K from the experimental results. The drain current (${I}_{D}$), electric field (${E}{-}\textsf {field}$), and ${I}_{\textsf {II}}$ are plotted in time. We observe that ${I}_{\textsf {II}}$ increase as ${E}{-}\textsf {field}$ reduces which indicates that ${E}$ -field does not primarily contribute to ${I}_{\textsf {II}}$. Furthermore, ${I}_{D}$ shows two distinct behaviors: 1) ${I}_{\textit {II}} ({I}_{D}$) is constant at the beginning and 2) eventually “universal” ${I}_{\textsf {II}} ({I}_{D}$) is linear, i.e., ${I}_{\textsf {II}}={k}\times {I}_{D}$ where ${k} = \textsf {1}\textsf {0}^{-\textsf {3}}$ ; we also show that the electrons primarily contributing to ${I}_{D}$ are directly incapable of II due to insufficient energy ($< {E}_{g}$). Fischetti’s model showed that SBG-II is primarily caused by “hot” electrons that accept energy in an Auger-like process from “cold” drain electrons to enable SBG-II. We speculate that if ${I}_{D}$ electrons “heat-up” the cold drain electrons, which would further energize the hot electrons to produce the observed ${I}_{\textsf {II}}{(}{I}_{D}$) universal dependence. [ABSTRACT FROM AUTHOR]