Anomalous Conductivity Switch Observed in Treated Hafnium Diselenide Transistors

Abstract

Layered hafnium diselenide (HfSe2) is an emerging Van der Waals semiconductor in which a hafnium layer is sandwiched between two selenium layers. Owning to its indirect band gap with magnitudes close to silicon's band gap and high predicted carrier mobility, hafnium diselenide material is a strong candidate for device applications. Here, the effect of laser treatment on 2H‐ HfSe2 devices is shown in ambient conditions using µ‐Raman spectroscopy. It is shown that an emerging Raman peak evolves with increasing laser exposure time. It is also shown that top‐down fabricated 2H‐HfSe2 devices exhibit an anomalous p‐type behavior post laser treatment, with Ion/Ioff ratio as high as 103. This anomalous conductivity change can be observed after thermal and electrical annealing. For bottom‐up devices, it is observed that p‐type conductivity with remarkable Ion/Ioff ratio reaching 104. This conductivity switch can also be shown on 1T‐HfSe2 devices post laser irradiation and high Vds bias treatments. Based on the circuit model, this conductivity switch is attributed to contact doping caused by an increase in the Schottky barrier height at each contact, which shifts the Fermi energy closer to the valance band. These results demonstrate a unique conductivity switching mechanism for HfSe2‐FET devices.

Wafer‐Scale 2D Hafnium Diselenide Based Memristor Crossbar Array for Energy‐Efficient Neural Network Hardware

“…Hafnium diselenide (HfSe 2 ) is a 2D semiconductor with indirect bandgap, and variable resistive states have been reported in HfSe 2 -metal compounds, manifesting its potential for memristive devices. [28,29] Moreover, most HfSe 2 -based electronic devices are fabricated by exfoliated flakes due to the challenges associated with large-scale growth and fabrication. [29,30] In this work, a memristive CBA based on HfSe 2 is fabricated and implemented in neural network hardware.…”

“…[28,29] Moreover, most HfSe 2 -based electronic devices are fabricated by exfoliated flakes due to the challenges associated with large-scale growth and fabrication. [29,30] In this work, a memristive CBA based on HfSe 2 is fabricated and implemented in neural network hardware. The 2D polycrystalline HfSe 2 is grown by molecular beam epitaxy (MBE) with a controllable and uniform growth on wafer-scale substrate.…”

Impact of In Situ Oxidation‐Resulted High‐k Passivation Layer on Device Stability and Mobility Improvement

“…This formation of a-Se bears considerable implications not only for the conductivity characteristics of the HfSe 2 channel but also for the potential phase transition from the 2H-HfSe 2 structure to the 1T phase. [23,24] The simultaneous presence of the dual channel, consisting of MoS 2 and partially oxidized HfSe 2 , along with the border traps within HfSe 2 , synergistically contributes to the pronounced electrical hysteresis observed in the transfer curve of a MoS 2 transistor capped with HfSe 2 . The device in this state is relatively unstable, and even a 10-second gate bias stress results in significant changes to the transfer curve due to charge exchange between the channel and the border traps.…”

Lattice Transformation from 2D to Quasi 1D and Phonon Properties of Exfoliated ZrS2 and ZrSe2

“…The observation of this peak has been reported before in transition metal selenide such as HfSe2 and is assigned to amorphous Se atoms, where at a sufficient optical energy, bonded Se atoms dissociate from transition metal (i.e., Zr). [43,46,47] It is possible that the emergence of amorphous Se atoms could contribute to lower thermal Raman downshift since these Se atoms can create a decay (cooling) path for optical phonons. Accordingly, in our localized laser heating of ZrSe2 and ZrSe3 Raman modes, temperature estimation values at high laser power are not fully accurate compared to temperature values at lower laser power, where this Se peak does not appear.…”