Epitaxial growth and electrical properties of ultrathin La2Hf2O7 high-k gate dielectric films

Ultrathin La2Hf2O7 (LHO) high-k gate dielectric films (∼3.4 nm) have been epitaxially grown on Si (0 0 1) substrates through a pulsed laser deposition system. The epitaxial growth characteristics, composition, interface with Si, optical band gap, and electrical properties of the ultrathin LHO films have been investigated by in situ reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS) and transmittance spectroscopy, as well as semiconductor characterization analysis. Results show that ultrathin LHO film grown at 800 °C shows a good crystallinity and no obvious interfacial layer forms. La is deficient and oxygen is slightly excessive in LHO film. The epitaxial LHO film has a band gap of ∼5.7 eV. The gate leakage current density Jg of the ultrathin epitaxial LHO film follows the space-charge limited conduction mechanism and Jg is ∼0.3 A/cm2 at a gate voltage of 1 V. Additionally, a suitable permittivity ∼ 16.7, a small hysteresis ∼ 30 mV and a low capacitance equivalent thickness ∼ 0.79 nm have been obtained.