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- ab inito calculations (2)
- high-k (2)
- Capacitance-voltage measurements (1)
- High-k dielectrics (1)
- Interface reaction (1)
- Photoelectron spectroscopy (1)
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Institute
BTU
Interface science of virtual GaN substrates on Si(111) via Sc2O3/Y2O3 buffers: Experiment and Theory
(2013)
Band structure and electrical properties of MBE grown HfO2 - based alkaline earth perovskites
(2010)
Ultra thin dielectric films (<20 nm) deposited on TiN electrodes are interesting for MIM capacitor application. High capacitance density and dielectric permittivity must be accompanied by extremely low leakage currents (10−8 A/cm2) at bias 0.5 V. To achieve such low leakage currents, high band gap and proper band alignment is required. Occupied electronic states can be probed with standard laboratory photoemission methods. Probing of unoccupied states is more challenging. Synchrotron based PES in combination with XAS forms a powerful method to study the band alignment. ASAM end station located at the U 49/2 PGM 2 beamline of BESSY II (Berlin) offers excellent conditions for performing such measurements. We investigated HfO2 - based alkaline earth perovskite - BaHfO3 with subsequent admixture of TiO2, resulting in formation of BaHf0.5Ti0.5O3 compound. The analysis of data indicates that band gap for HfO2 is similar to BaHfO3 and amounts 5.8 eV; for BaHf0.5Ti0.5O3 it decreases to 3.8 eV. We conclude that the addition of TiO2 to BaHfO3 increases significantly the dielectric permittivity but also impacts the band gap alignment. The conduction band offset shrinks, influencing the leakage current behavior.
Band gap and electronic structure determination with XAS and UPS of thin Pr-oxide films on Si(111)
(2008)
Pr2O3 is currently under consideration as a potential alternative gate dielectric candidate for sub-0.1 µm Complementary Metal Oxide Semiconductor (CMOS) technology. For all thin gate dielectrics, the interface with silicon plays a key role, and in most cases is a dominant factor in determining overall electrical properties. We studied the Pr2O3/Si(001) interface by a non-destructive depth profiling using synchrotron radiation photo-electron spectroscopy and ab initio calculations. Our results provide evidence that a chemical reactive interface exists consisting of a mixed Si-Pr oxide such as (Pr2O3)x(SiO2)1−x, typically in non-stoichiometric composition. There is no formation of neither an interfacial SiO2 nor interfacial silicide: all Si-Pr bonds are oxidized and all SiO4 units dissolve in the Pr oxide. Interfacial silicates like (Pr2O3)x(SiO2)1−x are promising high-k dielectric materials because they represent incremental modification of SiO2 films by Pr ions so that the interface characteristics can be similar to Si-SiO2 interface properties. Under ultrahigh vacuum conditions, silicide formation is observed when the silicate film is heated above 800∘C. The praseodymium silicate system observed at the interface between Si(001) and Pr2O3 offers greater flexibility towards integration of Pr2O3 into future CMOS technologies.