Trap States in HfO₂/Ga₂O₃ and Al₂O₃/Ga₂O₃ Metal Insulator Semiconductor Structures

Abstract

HfO₂/(010) bulk Ga₂O₃ and HfO₂/(001) epi layer Ga₂O₃ metal insulator semiconductor (MIS) structures were prepared by atomic layer deposition of HfO₂ at 300 °C with subsequent annealing at 500 °C. In addition, Al₂O₃/(001) epilayer Ga₂O₃ MIS were also fabricated by e-beam deposition at room temperature. The structures were characterized by capacitance–voltage C–V and current–voltage I–V measurements in the dark and with monochromatic photoexcitation in the spectral range 1.3–4.5 eV and by deep level transient spectroscopy (DLTS). DLTS spectra measurements revealed the presence of interface states with the density D_it peaking near E_c-0.5 eV at 8 × 10¹⁰ cm^–2 eV^–1 in HfO₂ MIS structures and D_it peaking near E_c-1.24 eV at a density of 1.1 × 10¹² cm^–2 eV^–1 in Al₂O₃ MIS structures. For both dielectrics, a high density of border trap-related charge of ∼10¹³ cm^–2 was detected by C–V measurements with illumination. DLTS measurements are useful in the characterization of interfacial states in Ga₂O₃ MIS with high leakage current in accumulation, for which standard C–V based techniques present problems.