Effects of intrinsic defects on effective work function for Ni/HfO2 interfaces

Abstract

The effective work functions and formation energies for Ni/HfO2 interfaces with and without defects, including interfacial intrinsic atom substitution and atom vacancy in interfacial layer were studied by first-principles methods based on density functional theory (DFT). The calculated results of the formation energies indicate that the interfaces with O-Ni combining bonds in the interfacial region are more energetically favorable and a small amount O vacancy is comparatively easy to form in O-Ni interface, especially under O-rich situation. Moreover, the results of our calculations also reveal that, (1) the effective work functions strongly depend on the type of interface, interface roughness and atom substitution content in the interface region;(2) for Hf-Ni interfaces, two calculated effective work functions without and with Ni substitutions in whole interfacial Hf layer are good for nMOS and pMOS effective work function (EWF) engineering, respectively; (3) the EWFs are sensitive to Hf vacancy rather than Ni vacancy in interfacial layer for Hf-Ni interfaces; (4) oxygen vacancies can result in a © 2016. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/ 2 decrease of effective work function for O-Ni interfaces. Additionally, we establish an expectedtheoretical relationship that variations of the EWFs are in proportion to that of interface dipole density. Finally, ionic valence state and occupied state are used to qualitatively analyze and explain the effects of interfacial defects on the EWF in metal-oxide interfaces. Our work suggests that controlling interfacial intrinsic atom substitution and interface roughness are attractive and promising ways for modulating the effective work function of Ni/HfO2 interfaces. IntroductionTo solve the problems arising from the aggressive size downscaling of metal-oxide-semiconductor field-effect transistor (MOSFET), both high dielectric constant "high-k" gate dielectric and metal gate electrode are required to replace the traditional SiO2 gate dielectric and polycrystalline Si, respectively [1,2]. Because of its high dielectric constant, excellent thermal stability and compatibility with various technical requirements, Hafnium oxide (HfO2) has emerged as one of the most preferred gate oxides in high-k metal gate technology [2-4]. While for desirable metal gate, an appropriate effective work function needs to satisfy the requirement that it lies near the valence and conduction band edges of Si substrate (about 4.1eV and 5.2eV for negative MOS [nMOS] and positive MOS [pMOS], respectively) [5]. There have been many studies [6-16] on tuning the effective work function (EWF) of metal-high-k gate stacks and several accompanying possible modulation methods for the EWF, such as binary 3 alloys [6], bilayer metal gate technology [7], and atomic dopant [8][9][10][11][12][13][14][15]. However, even so, the EWF is difficult to control, especially for pMOS, due to its extreme sensitivity to a number of factors th...

Effects of graphene intercalation on dielectric reliability of HfO2 and modulation of effective work function for Ni/Gr/c-HfO2 interfaces: first-principles study

“…The interface EWF can be estimated using potential-line-up method, as schematically shown in Fig. 2(a) , and the interface EWF is generally estimated as follows 41 – 43 Where , and in the first term is the electron affinity, band gap and the valence band maximum (VBM) of HfO 2 , respectively. As is well-known, DFT underestimates the oxide gap.…”

“…While the second term Δ V is determined by the charge transfer that takes place in interfacial region. More detailed estimation of interface EWF can be found in our previous study 43 . For Ni(111)/Gr/HfO 2 (111) interface, when the graphene is inserted into Ni(111)/HfO 2 (111) interface, it would only change interfacial structure but Ni and HfO 2 bulk electronic structures were not affected.…”

Material descriptors for photocatalyst/catalyst design

“…In the present review, we focus on a number of material descriptors, including the work function (Lang & Kohn, ), dipole moment (Rittner, ), d‐band centers (Hammer & Nørskov, ), Fermi softness (Huang, Xiao, Lu, & Zhuang, ), as well as their influence on the three above‐mentioned key processes that determine the performance of photocatalysis. Moreover, all these descriptors mentioned above can also be used in other kinds of catalytic systems (Dahl, Logadottir, Jacobsen, & Nørskov, ; Stamenkovic, Mun, Mayrhofer, Ross, & Markovic, ; Zhong, Xu, Zhang, Liao, & Huang, ). By presenting application examples of these descriptors from a mechanistic viewpoint, we aim to achieve three goals: firstly, to inspire new perspectives toward photocatalyst/catalyst design and optimization based on descriptors; secondly, to provide some experimental guidance upon analyzing the descriptor‐performance relation; and finally, to point out some remaining challenges and opportunities for the usage of descriptors.…”