Electrical properties of ultrathin HfO₂ gate dielectrics on partially strain compensated SiGeC/Si heterostructures

Ultrathin HfO₂ gate dielectrics have been deposited on strained Si_0.69Ge_0.3C_0.01 layers by rf magnetron sputtering. The polycrystalline HfO₂ film with a physical thickness of ∼6.5 nm and an amorphous interfacial layer with a physical thickness of ∼2.5 nm have been observed by high resolution transmission electron microscopy (HRTEM). The electrical properties have been studied using metal-oxide-semiconductor (MOS) structures. The fabricated MOS capacitors on Si_0.69 Ge_0.3C_0.01 show an equivalent oxide thickness (EOT) of 2.9 nm, with a low leakage current density of ∼4.5 × 10 ^{- 7} A/cm² at a gate voltage of -1.0 V. The fixed oxide charge and interface state densities are calculated to be 1.9 × 10¹² cm^{- 2} and 3.3 × 10 ¹¹ cm^{- 2}eV^-1, respectively. The temperature dependent gate leakage characteristics has been studied to establish the current transport mechanism in high-k HfO₂ gate dielectric to be Poole-Frenkel one. An improvement in electrical properties of HfO₂ gate dielectrics has been observed after post deposition annealing in O₂ and N₂ environments.