Papers by Jarek Dąbrowski
Solid State Communications, 2015
This paper reviews the experimental and theoretical state of the art in ballistic hot electron tr... more This paper reviews the experimental and theoretical state of the art in ballistic hot electron transistors that utilize two-dimensional base contacts made from graphene, i.e. graphene base transistors (GBTs). Early performance predictions that indicated potential for THz operation still hold true today, even with improved models that take non-idealities into account. Experimental results clearly demonstrate the basic functionality, with on/off current switching over several orders of magnitude, but further developments are required to exploit the full potential of the GBT device family. In particular, interfaces between graphene and semiconductors or dielectrics are far from perfect and thus limit experimental device integrity, reliability and performance.
Materials Science in Semiconductor Processing
Topics in Applied Physics
ABSTRACT In the nearest future, a dielectric with a dielectric constantk several times higher tha... more ABSTRACT In the nearest future, a dielectric with a dielectric constantk several times higher than that of SiO2 will be needed for the fabrication of CMOS (Complementary Metal-Oxide-Semiconductor) devices. Numerous metal oxides and silicates are investigated as candidates and various deposition and annealing techniques are being developed to improve the film quality. These techniques try to utilize the effects attributed to alloying, incorporation of nitrogen, gettering of oxygen, etc. At the same time, the basic knowledge on the microscopic properties of these materials needs improvement, particularly in the case of rare-earth oxides. We present our fundamental understanding of point defects in Pr-based dielectrics (PrO1.5, PrO2, PrO1.75+delta, and PrSiO3.5) in the context of their influence on the electrical properties of the Metal Oxide Semiconductor (MOS) stack. From this point of view, there are three major issues associated with the presence of point defects: bulk charge traps, Trap Assisted Tunneling (TAT) centers, and electrically active interface states. The paper focuses on the first of these issues, as seen from the perspective of ab initio total energy calculations for atomic and electronic structures of point defects. We discuss the dependence of point defect formation on the chemical potential of oxygen and the role of impurities such as moisture, silicon, and boron. In particular, we derive a model of Si-related fixed charge and argue that this model is valid also for typical high-k dielectrics and for thermal SiO2/Si films.
Materials Science in Semiconductor Processing, 2000
Dopant atoms segregate to SiO2/Si(001) interfaces. This causes problems during manufacture of sub... more Dopant atoms segregate to SiO2/Si(001) interfaces. This causes problems during manufacture of submicron microelectronic devices. On the basis of ab initio calculations, we identify the physical mechanism by which P atoms are trapped and deactivated at SiO2/Si(001). We argue that segregation can occur to defected as well as to defect-free interfaces. In the latter case, the interfacial stress stabilizes pairs of threefold-coordinated phosphorus atoms. Implications for Complementary Metal-Oxide-Semiconductor (CMOS) process design are discussed.
Physical Review B, 2002
Dopant atoms can segregate to SiO 2 /Si͑001͒ interfaces and be deactivated there. Using phosphoru... more Dopant atoms can segregate to SiO 2 /Si͑001͒ interfaces and be deactivated there. Using phosphorus as a typical example of a donor and guided by results of ab initio calculations, we present a model of donor segregation. We find that P is trapped at the interface in the form of threefold-coordinated atoms. The atomic detailed configuration and the process of P incorporation depend on P concentration C P in the vicinity of the interface. At low C P , phosphorus atoms prefer to substitute Si atoms with dangling bonds. At high C P , phosphorus pairs are formed. At intermediate C P , ͑around 10 17-10 19 cm Ϫ3 ͒ segregation occurs to sites associated with interface roughness and to interface Si-Si bridges, and is mediated by diffusion and annihilation of Si dangling bonds and by reoxidation during oxide annealing. Making diffusion of dangling bonds more difficult ͑for example, by nitridation͒ should, therefore, reduce the trapping efficiency of SiO 2 /Si͑001͒ in the technologically important regime of intermediate C P .
MRS Proceedings, 2004
ABSTRACTWe have fabricated Pr-based high-k gate dielectric films by physical vapor deposition of ... more ABSTRACTWe have fabricated Pr-based high-k gate dielectric films by physical vapor deposition of metallic Pr on SiO2 under ultra-high vacuum (UHV) conditions at room temperature, followed by oxidation and annealing steps. The films have been analyzed by electrical measurements, X-ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM). Some insight into the physical processes involved has been obtained from ab initio calculations. The high-k gate stacks consist of a SiO2-based buffer with an enhanced dielectric constant and a Pr silicate barrier with a high dielectric constant. The role of the buffer is to preserve the high quality of the SiO2/Si(001) interface, and the role of the barrier is to keep the tunneling currents low by increasing its physical thickness. A Pr film deposited on a 1.8 nm SiO2 layer, oxidized at room temperature by air, and annealed in N2 atmosphere with O2 partial pressure of 10−3 mbar results in a stack with the Capacitance Equivalen...
Pr and La oxide thin films were investigated in the context of their application as high-k dielec... more Pr and La oxide thin films were investigated in the context of their application as high-k dielectrics in Complementary Metal Oxide (CMOS) technology. The films were deposited by Molecular Beam Epitaxy (MBE) on bare and TiN-covered Si(001). The influence of growth and post-deposition temperature on the composition and electrical parameters was studied. We observed Si penetration from bare Si(001) into the growing film. On the basis of the results of Capacitance-Voltage (CV) measurements and ab initio calculations we conclude that Si is a source of defects responsible for leakage. We also addressed the mechanism of the formation of the interface region between Pr 2 O 3 and Si(001) and the role of moisture in this process. We argue that substrate oxidation is mediated by OH which, in contrast to oxygen, can penetrate the interfacial silicate even at room temperature. In unprotected films, a low-density interfacial layer is formed in this way.
Physica B: Condensed Matter, 1999
Microelectronic Engineering
Surface Review and Letters, 2003
Activation energies and atomic geometries associated with Si adsorption and desorption processes ... more Activation energies and atomic geometries associated with Si adsorption and desorption processes on the Si face of SiC (0001) have been obtained from in situ reflection high-energy electron diffraction measurements and ab initio pseudopotential calculations. During the initial stage of Si deposition, the SiC (0001) surface develops a series of superstructures, depending on temperature and Si coverage. A kinetic diagram of the structural transformations during Si exposure or annealing is outlined and the adsorption energy Ea is determined. The latter is found to be strongly affected by the surface structure and coverage, changing from 4.5 eV to 1.6 eV as the geometry of the Si adlayer changes from [Formula: see text] to (3×3). These observations are interpreted with the help of ab initio pseudopotential calculations. It is concluded that [Formula: see text] measured on [Formula: see text] corresponds to adsorption at adatom vacancy while Ea3=1.6 eV measured on (3×3) corresponds to ad...
International Journal of Quantum Chemistry, 1990
ABSTRACT
Surface Science, 2002
Pr2O3 may be an alternative high-K gate dielectric material for silicon integrated circuits, i.e.... more Pr2O3 may be an alternative high-K gate dielectric material for silicon integrated circuits, i.e., it has a dielectric constant K⩾25 and is currently under consideration as potential replacement for SiO2 as the gate dielectric material for sub-0.1 μm complementary metal-oxide-semiconductor technology. Using scanning tunneling microscopy and X-ray photoelectron spectroscopy, we show that the initial stages of heteroepitaxial Pr2O3 grown on
We demonstrate molecular beam growth of graphene on biotite mica substrates at temperatures below... more We demonstrate molecular beam growth of graphene on biotite mica substrates at temperatures below 1000 • C. As indicated by optical and atomic force microscopy, evaporation of carbon from a high purity solid-state source onto biotite surface results in the formation of single-, bi-, and multilayer graphene with size in the micrometer regime. It is shown that the graphene grown directly on mica surface is of very high crystalline quality with the defect density below the threshold detectable by Raman spectroscopy. The interaction between graphene and the mica substrate is studied by comparison of the Raman spectroscopy and atomic force microscopy data with the corresponding results obtained for graphene flakes mechanically exfoliated onto biotite substrates. Experimental insights are combined with density functional theory calculations to propose a model for the initial stage of the van der Waals growth of graphene on mica surfaces. This work provides important hints on how the direct growth of 1 arXiv:1205.6591v1 [cond-mat.mes-hall] 30 May 2012 high quality graphene on insulators can be realized in general without exceeding the thermal budget limitations of Si technologies.
MRS Online Proceeding Library
Hexagonal boron nitride (h-BN) considered to be an attractive substrate for graphene, because the... more Hexagonal boron nitride (h-BN) considered to be an attractive substrate for graphene, because the interaction between h-BN and graphene is weak enough for high carrier mobility to be retained in graphene but strong enough to allow for some epitaxial relationship. The purpose of this study is to elucidate by experimental and theoretical means the role, which defects in the h-BN substrate play in the nucleation and growth of graphene. We deposited C atoms by molecular beam epitaxy (MBE) on exfoliated h-BN and evaluated the resulting films by Raman spectroscopy and by atomic force microscopy (AFM). The deposition resulted in the formation of nanocrystalline graphene with average domain size up to several dozen nanometres. Thereafter, we analysed the atomistic details of the deposition process by ab initio density functional theory (DFT) and we linked the DFT and MBE data by random walk theory. Graphene appears to nucleate around extended defects in virgin h-BN. The DFT analysis reveals...
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Papers by Jarek Dąbrowski