Characteristics of hafnium silicate as gate dielectric in n-GaN capacitors were investigated. The Hf0.57Si0.43Ox, Hf0.64Si0.36Ox and HfO2 films exhibited high dielectric constants of 15.4, 15.9, and 17.6, respectively. The Hf0.57Si0.43Ox and Hf0.64Si0.36Ox films, which had an amorphous structure, showed superior properties, including a minimal flatband voltage (Vfb) hysteresis (≤70 mV) and a small Vfb shift (≤−0.45 V), as well as a low interface state density (~4 × 1011 cm−2 eV−1 at −0.4 eV from conduction band), and a high breakdown electric field (≥8.6 MV cm−1) compared to those of a polycrystalline HfO2 film.
We systematically investigated characteristics of Pt-gated capacitors with four kinds of gate insulators such as Hf0.57Si0.43Ox, Hf0.64Si0.36Ox, HfO2, and Al2O3. The Hf0.64Si0.36Ox films fabricated by post-deposition annealing (PDA) at 800°C in O2 (PDO), N2(PDN), and 3% H2 (PDH) ambient exhibited quite different characteristics. After PDO, the Hf0.64Si0.36Ox film was partially crystallized and had a thick interfacial layer at the n-GaN/Hf0.64Si0.36Ox interface, while the Hf0.64Si0.36Ox films after PDN and PDH maintained an amorphous structure. The PDH capacitor exhibited an order of magnitude larger interface state density than the PDN capacitor, indicating that the PDN process can produce superior Hf0.64Si0.36Ox film. The Hf0.57Si0.43Ox,Hf0.64Si0.36Ox, HfO2, and Al2O3 films after PDA at 800°C in N2 were 15.4, 15.9, 17.6, and 9, respectively. The HfO2 and Al2O3 films consist of polycrystalline structure while the Hf0.57Si0.43Ox and Hf0.64Si0.36Ox films maintain an amorphous structure. The different structure strongly affected to electrical properties. The Hf0.57Si0.43Ox and Hf0.64Si0.36Ox capacitors showed superior electrical properties such as a minimal flatband voltage (V fb) hysteresis ( ≤ +70 mV) and a small V fb shift ( ≤ -0.46 V), as well asa low interface state density (~ 3 × 1011 cm-2eV-1 at -0.45 eV fromconduction band), and a high breakdown electric field ( ≥ 8.6 MV/cm) compared to those of the HfO2 and Al2O3 capacitors.
Hafnium silicate (HfSiOx) has been applied to AlGaN/GaN high-electron-mobility transistors (HEMTs) as a high κ gate dielectric. The (HfO2)/(SiO2) laminate structure was deposited on the AlGaN surface by a plasma-enhanced atomic layer deposition, followed by a post-deposition annealing at 800 °C. The HfSiOx-gate HEMT showed good transfer characteristics with a high transconductance expected from its κ value and a subthreshold swing of 71 mV/decade. For the metal–oxide-semiconductor (MOS) HEMT diode, we observed excellent capacitance–voltage (C–V) characteristics with negligible frequency dispersion. The detailed C–V analysis showed low state densities on the order of 1011 cm−2 eV−1 at the HfSiOx/AlGaN interface. In addition, excellent operation stability of the MOS HEMT was observed at high temperatures up to 150 °C.
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