<i>Ab initio</i> calculation of effective work functions for a TiN/HfO2/SiO2/Si transistor stack

Prodhomme, Pierre-Yves; Fontaine‐Vive, Fabien; Geest, Abraam vand Der; Blaise, P.; Even, Jacky

doi:10.1063/1.3609869

Cited by 24 publications

(17 citation statements)

References 22 publications

(22 reference statements)

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“…[35] The case of incoherent interfaces like in a relaxed buried semiconductor QD or a complex stack of metal oxide semiconductors can hardly be treated at the envelope function level. [44,51] DFT is a valuable tool in such cases. Effective mass or k.p approaches are still interesting to easily compute various bulk physical quantities like the density of states or the optical dielectric constants.…”

Section: Effective Mass Modeling Of Quantum Confinementmentioning

confidence: 99%

Understanding Quantum Confinement of Charge Carriers in Layered 2D Hybrid Perovskites

2014

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Keywords: 2D materials, density functional calculations, hybrid perovskites, quantum confinement, semiempirical calculations Layered Hybrid Organic Perovskites (HOP) structures are a class of low-cost twodimensional (2D) materials that exhibit outstanding optical properties, related to dielectric and quantum confinement effects. While modeling and understanding of quantum confinement are well developed for conventional semiconductors, such knowledge has still to be gained for 2D HOP. In this work, concepts of effective mass and quantum well are carefully investigated and their applicability to 2D HOP is discussed. For ultrathin layers, the effective mass model fails. Absence of superlattice coupling and importance of non-parabolicity effects prevents the use of simple empirical models based on effective masses and envelope function approximations. We suggest an alternative approach where 2D HOP are treated as composite materials and introduce a first principles approach to band offsets calculations. These findings may also be relevant for other classes of layered 2D functional materials.

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Section: Effective Mass Modeling Of Quantum Confinementmentioning

confidence: 99%

Understanding Quantum Confinement of Charge Carriers in Layered 2D Hybrid Perovskites

2014

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“…24,[31][32][33][34] The G 0 W 0 correction can also be used to correct the location of the valence bands for insulators and the Fermi energy for metals in relation to the electrostatic potential of a material, and has recently been shown to closely approach the effective work function for a complete gate stack. 22 Based upon the encouraging results obtained for Si/SiO 2 , 24,33 Si/HfO 2 34 and SiO 2 /HfO 2 22 interfaces, we used a G 0 W 0 correction hoping to provide results sufficiently close to experiment. The G 0 W 0 calculation is a perturbational approach which is generally used to correct the energy levels coming from a DFT calculation.…”

Section: B G 0 W 0 Correctionsmentioning

confidence: 81%

“…[17][18][19] While many studies have been directed towards the building of new gate stacks, the specific HfO 2 /SiO 2 interface is only beginning to be well understood at the atomic scale, in relation to its structure and concerning the role of dopants. 2,8,12,13,[20][21][22][23][24] In order to render possible the theoretical study of the variability issue without including all possible structural factors that could be affected during the deposition processes or by the various thermal treatments, one has to carefully select the materials phases, interface orientations, chemistry of the interfaces, and dopants locations. As explained in detail in part III of this paper, we specifically deal with the variance of the orientation between monoclinic HfO 2 (m-HfO 2 ) and β-cristobalite SiO 2 (β-SiO 2 ) by constructing and calculating the VBO of low strain interfaces using ab initio methods.…”

Section: Introductionmentioning

confidence: 99%

Ab initiostudy of the electrostatic dipole modulation due to cation substitution in HfO2/SiO2interfaces

2012

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The interface between HfO 2 and SiO 2 is of much technological interest for complementary metal-oxide semiconductor (CMOS) technology in microelectronic devices. The valence band offset between HfO 2 and SiO 2 is a property of particular importance for this interface because it can be modulated by adding substitutional cations like Al, La, and Mg. We study the effects of these substitutional cations within this interface by using ab initio techniques in order to obtain the electrostatic dipole modulation and the corresponding change in the valence band offset in relation to dopant free reference HfO 2 /SiO 2 interfaces. Al, La, and Mg are substituted for both Hf and Si atoms close to the interface during a detailed analysis of the dipole at the microscopic scale. This reproduces not only the experimental trends, but also demonstrates that the effects of the dopants are strongly dependent upon their positions and their chemical environments. Specifically, the modulation of the charge distribution by the dopants shows a complicated structure consisting of several peaks that contribute to the interfacial dipole centered around the oxygen atoms that bridge between the HfO 2 and the SiO 2 . We also include a first-order G 0 W 0 correction to recover band offset results compatible with the experimental values.

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“…Thus, it has limited predictive capability. A very recent work by Prodhomme et al 35 uses the band offset method to compute the EWF going beyond standard LDA-DFT. They considered the entire stack of a MOSFET involving Si/SiO 2 /HfO 2 /TiN.…”

Section: Effective Work Function Engineeringmentioning

confidence: 99%

“…Another approach to computing the EWF is through the band offset method. 13,34,35 In this method, the EWF is obtained by subtracting the valence band offset between HfO 2 and the metal, from the experimental band gap of the HfO 2 , and then by adding the experimental electron affinity of the HfO 2 . However, this method suffers from the well known problem of the DFT, namely, the errors in the band structure (extracted from the bulk calculations on the materials forming the interface) as well as in the bandline up (obtained from the interface calculation).…”

Section: Effective Work Function Engineeringmentioning

confidence: 99%

Role of point defects and HfO2/TiN interface stoichiometry on effective work function modulation in ultra-scaled complementary metal–oxide–semiconductor devices

Pandey¹,

Sathiyanarayanan²,

Kwon³

et al. 2013

Journal of Applied Physics

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We investigate the physical properties of a portion of the gate stack of an ultra-scaled complementary metal-oxide-semiconductor (CMOS) device. The effects of point defects, such as oxygen vacancy, oxygen, and aluminum interstitials at the HfO2/TiN interface, on the effective work function of TiN are explored using density functional theory. We compute the diffusion barriers of such point defects in the bulk TiN and across the HfO2/TiN interface. Diffusion of these point defects across the HfO2/TiN interface occurs during the device integration process. This results in variation of the effective work function and hence in the threshold voltage variation in the devices. Further, we simulate the effects of varying the HfO2/TiN interface stoichiometry on the effective work function modulation in these extremely-scaled CMOS devices. Our results show that the interface rich in nitrogen gives higher effective work function, whereas the interface rich in titanium gives lower effective work function, compared to a stoichiometric HfO2/TiN interface. This theoretical prediction is confirmed by the experiment, demonstrating over 700 meV modulation in the effective work function.

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Ab initio calculation of effective work functions for a TiN/HfO2/SiO2/Si transistor stack

Cited by 24 publications

References 22 publications

Understanding Quantum Confinement of Charge Carriers in Layered 2D Hybrid Perovskites

Understanding Quantum Confinement of Charge Carriers in Layered 2D Hybrid Perovskites

Ab initiostudy of the electrostatic dipole modulation due to cation substitution in HfO2/SiO2interfaces

Role of point defects and HfO2/TiN interface stoichiometry on effective work function modulation in ultra-scaled complementary metal–oxide–semiconductor devices

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