Optical properties of epitaxial SrHfO3 thin films grown on Si

Abstract

The perovskite SrHfO3 can be a potential candidate among the high-permittivity materials for gate oxide replacement in future metal-oxide semiconductor field-effect transistor technology. Thin films of SrHfO3 were grown by molecular beam epitaxy and compared with SrTiO3 films. Their optical properties were investigated using spectroscopic ellipsometry and analyzed with respect to their structural properties characterized by x-ray diffractometry, atomic force microscopy, and transmission electron microscopy. A band gap of Eg=6.1±0.1eV is measured optically, which renders this material better suited for gate dielectric applications than SrTiO3 with Eg∼3.4eV. At similar equivalent oxide thickness, SrHfO3 also exhibits lower gate leakage current than SrTiO3 does.

Atomic layer deposition of crystalline SrHfO3 directly on Ge (001) for high-k dielectric applications

“…Polycrystalline SHO films are reported to have a dielectric constant up to k $ 35, 24,28 leading to an EOT of less than 0.6 nm with a 5 nm film using the ratio of k/3.9. However, other studies have reported lower dielectric constants (k $ 20) for SHO, 26,32 similar to the binary oxide HfO 2 . Finally, SHO has a large band gap of 6.1 eV with favorable conduction band offset ($2.2 eV) and valence band offset ($3.2 eV) with Ge.…”

“…Finally, SHO has a large band gap of 6.1 eV with favorable conduction band offset ($2.2 eV) and valence band offset ($3.2 eV) with Ge. 26,34 This is in contrast with Ti-based perovskites, where the Ti 3d states yield negligible conduction band offsets with Si and Ge ($0.1-0.5 eV). 21,22,35 A direct comparison between SHO and STO films on Si (001) has shown a reduction in gate leakage by 4 orders of magnitude for SHO versus STO.…”

“…[24][25][26][27][28][29][30][31][32] In some early work, crystalline SHO was investigated as a future gate dielectric material for Sibased devices. 25,27 The SHO films were grown by molecular beam epitaxy (MBE) on Si (001) despite the 6% lattice mismatch.…”

“…21,22,35 A direct comparison between SHO and STO films on Si (001) has shown a reduction in gate leakage by 4 orders of magnitude for SHO versus STO. 26 Recently, we reported the growth of single crystal STO (a ¼ 3.905 Å ) on Ge (001) by atomic layer deposition (ALD) followed by post-deposition annealing in vacuum. 23 Capacitor structures revealed a large dielectric constant (k $ 90) for the STO films, but a high leakage current of $10 A/cm 2 for an applied field of 0.7 MV/cm.…”

Enhanced electrical and magnetic properties in La0.7Sr0.3MnO3thin films deposited on CaTiO3-buffered silicon substrates

“…1 28 and SrHfO 3 . 29,30 The latter two, SrZrO 3 and SrHfO 3 , with pseudocubic lattice constants of 4.101 Å and 4.070 Å at room temperature, respectively, lie off the top of Fig. 1.…”