Charge trapping and recovery in ALD HfO₂/β-Ga₂O₃ (010) MOS capacitors

The reliability of atomic layer deposited HfO₂ β-Ga₂O₃ (010) MOS capacitors (MOSCAPs) was tested using constant voltage stress measurements. The HfO₂/β-Ga₂O₃ MOSCAPs showed significant positive flatband voltage shifts (ΔV _fb) of up to +1.3 V after 4.3 × 10³ s stress, likely due to electron trapping in the dielectric in border traps. Results indicate there may exist an electric field threshold between 0.98 and 1.23 MV cm⁻¹ for electron trapping to occur in these MOSCAPs. Deep ultra-violet (DUV) illumination enables full recovery from the charge trapping. In contrast, HfO₂/Si MOSCAPs do not recover under DUV illumination and exhibit smaller voltage shifts upon initial testing. We thus surmise that the type-II band alignment between HfO₂ and β-Ga₂O₃ enables full recovery from stress-induced charge trapping via photogeneration of electron–hole pairs and hole transport across the negative valence band offset. This hypothesis is borne out by the observation of photo-current in the HfO₂/β-Ga₂O₃ MOSCAPs when biased in depletion. In sum, HfO₂/β-Ga₂O₃ MOS structures appear to be susceptible to flatband voltage shifts during stress bias due to the availability and accessibility of border traps. This work highlights the unique challenges in forming reliable ultra-wide band gap MOS devices, due to the significant role that border traps in the lower half of the insulator band gap play in bias stress response. (letter)