Transient Phenomena in Sub-Band Gap Impact Ionization in Si NIPIN Diode

Abstract

Sub-band-gap (SBG) impact ionization (II) enables steep subthreshold slope that enables devices to overcome the thermal limit of 60mV/decade. This phenomenon at low voltage enables various applications in logic, memory and neuromorphic engineering. Recently, we have demonstrated sub-0.2V II in NIPIN diode experimentally primarily based on the steady-state analysis. In this paper, we present the detailed experimental transient behavior of SBG-II in NIPIN. 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 (i) recombination-generation (RG) and (ii) over the barrier (OTB) where OTB dominates when barrier height $ phy_b<0.59eV $. Second, we analytically extract the SBG II current (Iii) at 300K from experimental results. The drain current (Id), the electric field (E-field), and Iii are plotted in time. We observe that Iii increase as E-field reduces which indicates that E-field does not primarily contribute to Iii. Further, the Id shows two distinct behaviors (i) Iii (Id) is constant at the beginning and (ii) eventually universal Iii (Id) is linear, i.e. Iii=k X Id where $ k=10^-3$; We also show that the electrons primarily contributing to Id are directly incapable of II due to insufficient energy $(<Eg)$. 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 the Id electrons heat-up the cold drain electrons, which would further energize the hot electrons to produce the observed Iii (Id) universal dependence.