We present a non-local history-dependent model for impact ionization gain and noise in avalanche photodiodes (APDs) especially suited for staircase APDs. The model uses a simple energy balance equation to define effective electric fields valid also in the presence of band discontinuities which are then used to express the ionization coefficients. The model parameters have been calibrated against literature data for gain and noise in GaAs and AlxGa1−xAs (x = 0.2, 0.6, 0.8) p-in diodes. Application to experimental data for gain and noise in heterojunction and staircase SAM-APDs is reported to demonstrate the ability of the model in describing complex APD structures. It is found that, in spite of conduction band discontinuities being much larger than valence band ones, hole impact ionization contributes a significant degradation of the noise metrics in GaAs/AlGaAs staircase APDs. These non-trivial insights demonstrate the usefulness of the model to steer device design and optimization.

No abstract

The charge trapping properties of HfO2 thin films for application in charge trap memories are investigated as a function of high-temperature postdeposition annealing (PDA) and oxide thickness in the TaN/Al2O3/HfO2/SiO2/Si structure. The trap density (NT) in HfO2, extracted by simulating the programming transient, is in the 1019–1020 cm-3 range, and it is related to film thickness and PDA temperature. Diffusion phenomena in the stack play a significant role in modifying NT in HfO2 and the insulating properties of the Al2O3 layer. The memory performances for 1030 °C PDA are promising with respect to standard stacks featuring Si3N4.

The contact-end-resistance method is applied to TLM structures to characterize in-depth the graphene-metal contact and its dependence on the back-gate bias. Parameters describing the graphene-metal stack resistance are extracted through the widely used transmission line model. The results show inconsistencies which highlight application limits of the model underlying the extraction method. These limits are attributed to the additional resistance associated to the p-p + junction located at the contact edge, that is not part of the conventional transmission line model. Useful guidelines for a correct application of the extraction technique are provided, identifying the bias range in which this additional resistance is negligible. Finally, the contact-end-resistance method and the transmission line model are exploited to characterize graphenemetal contacts featuring different metals.

In part I of this paper, we study the physicochemical structure and the electrical properties of low-pressure-chemical-vapor-deposited silicon nitride (SiN) aimed to serve as storage layers for nonvolatile memory applications. An in-depth material analysis has been carried out together with a comprehensive electrical characterization on two samples fabricated with recipes yielding rather standard SiN and Si-rich SiN. The investigation points out the impact of SiN stoichiometry and hydrogen content on the electrical characteristics of gate stacks designed in view of channel hot-electron/hole-injection program/erase (P/E) operation and tunnel P/E operation. The extensive and detailed characterization establishes a sound experimental basis for the development of the physics-based trap models proposed in the companion paper