Defects and Low-Frequency Noise in Irradiated Black Phosphorus MOSFETs With HfO2 Gate Dielectrics

We have evaluated radiation-induced charge trapping and low-frequency noise in passivated black phosphorus (BP) MOSFETs with HfO
₂
gate dielectrics. Thinning the gate dielectric reduces total ionizing dose-induced threshold voltage shifts. The defect-energy distribution estimated from low-frequency noise measurements performed as a function of temperature decreases with increasing energy in as-processed devices. Local maxima in noise magnitude are observed in irradiated devices at activation energies of ~0.2 and ~0.5 eV. Larger defect-related peaks in noise magnitude in the range of 0.35-0.5 eV are observed after biased post-irradiation annealing, and/or vacuum storage of the devices after irradiation and annealing. Density functional theory calculations strongly support significant roles for O vacancies in HfO
₂
and H+ transport and reactions near the BP/HfO
₂
interface in the observed radiation response and low-frequency noise.