Doped HfO2 has become a promising candidate for non-volatile memory devices since it can be easily integrated into existing CMOS technology. Many dopants like Y, Gd, and Sr have been investigated for the stabilization of ferroelectric HfO2. Here, we report the fabrication of capacitors comprising ferroelectric HfO2 metal-insulator-metal structures with TiN bottom and top electrodes using the dopant Lu. Amorphous 5% Lu doped HfO2 was deposited by pulsed laser deposition and afterwards annealed to achieve the ferroelectric, orthorhombic phase (space group Pbc21). The polarization of the layers was confirmed by capacitance-voltage, polarization-voltage, and current-voltage measurements. Depending on the anneal temperature, the remanent polarization changes and the initial state of the oxide varies. The layer exhibits initially a pinched hysteresis up to an annealing temperature of 600 °C and an unpinched hysteresis at 700 °C. The maximum polarization is about 11 μC/cm2 which is measured after 104 cycles and stable up to 106 cycles. The influence of the layer thickness on the oxide properties is investigated for 10–40 nm thick HfLuO; however, a thickness dependence of the ferroelectric properties is not observed.

No abstract

III-V nitrides are interesting materials for a very wide variety of electronic and optoelectronic devices. In this study, their interaction with GdScO 3 (GSO), a ternary rare earth oxide, is investigated for MOS applications. We compare pulsed laser deposited amorphous and crystalline epitaxial GdScO 3 in terms of their band alignment with the underlying GaN substrate and the resulting electrical characteristics of the MOS stack. The crystal structure of GdScO 3 and GaN is investigated by means of x-ray diffraction, showing that crystalline oxide is growing epitaxially on GaN. X-ray photoelectron spectroscopy analysis shows a staggered band alignment with a GdScO 3-GaN valence band offset of 3.6-3.7 eV, which is reflected in a very asymmetric current-voltage behaviour of the MOS capacitors: breakdown at positive bias, significantly earlier for the crystalline oxide (around 5 MV/cm) compared to the amorphous oxide (around 8 MV/cm), and no breakdown up to a field of À14 MV/cm at negative bias. Transmission electron microscopy images show a crystalline, two-atom thick interface layer between GaN and both crystalline and amorphous GdScO 3 , which is thought to be an electron barrier between GSO and GaN and a possible source of the staggered band alignment. The electrical behaviour can be exploited for asymmetric nano-electronic devices. Published by AIP Publishing.

No abstract

No abstract

Ternary rare earth oxides are promising candidates for future gate oxides. Therefore GdScO3 and LaLuO3 were investigated with regard to their suitability as gate dielectric. The layers were deposited by pulsed laser deposition and the crystal structure, stoichiometry, layer roughness and band gap were investigated. GdScO3 can be grown hexagonal and amorphous and LaLuO3 can be grown hexagonal, orthorhombic and amorphous. All investigated layers revealed smooth surfaces, exhibited band gaps higher than 5 eV and a permittivity higher than 20. These results show that GdScO3 and also LaLuO3 are promising candidates as a future gate dielectric based on nitride semiconductor devices.