S. Mantl

Tuning of NiSi/Si Schottky barrier heights by sulfur segregation during Ni silicidation

sReceived 27 September 2004; accepted 14 December 2004; published online 2 February 2005dThe Schottky barrier height sSBHd of NiSi on Sis100d was tuned in a controlled manner by thesegregation of sulfur sSd to the silicide/silicon interface. S was implanted into silicon prior tosilicidation. During subsequent Ni silicidation, the segregation of S at the NiSi/Si interface leads tothe change of the SBH. The SBH of NiSi decreased gradually on n-Sis100d from 0.65 eV to 0.07 eVand increased correspondingly on p-Sis100d.© 2005 American Institute of Physics.fDOI: 10.1063/1.1863442gSelf-aligned silicidation is one of the key technologies inthe state-of-art complementary metal-oxide-semiconductorsCMOSd process to make Ohmic or Schottky contacts atsource/drain and gate. Amongst of them, NiSi silicide hasemerged as a leading choice in Si nanometer electronics dueto its low resistivity and high scalability. Recently, Schottkybarrier source/drain metal-oxide-semiconductor field-effecttransistors sMOSFETsd have been receiving a lot of attentionbecause of the lower parasitic series resistance at source/drain, possible zero junction depth and simpler fabricationprocess.

Band engineering and growth of tensile strained Ge/(Si)GeSn heterostructures for tunnel field effect transistors

In this letter, we propose a heterostructure design for tunnel field effect transistors with two low direct bandgap group IV compounds, GeSn and highly tensely strained Ge in combination with ternary SiGeSn alloy. Electronic band calculations show that strained Ge, used as channel, grown on Ge 1−xSnx (xu2009>u20099%) buffer, as source, becomes a direct bandgap which significantly increases the tunneling probability. The SiGeSn ternaries are well suitable as drain since they offer a large indirect bandgap. The growth of such heterostructures with the desired band alignment is presented. The crystalline quality of the (Si)Ge(Sn) layers is similar to state-of-the-art SiGe layers.

Effect of helium ion implantation and annealing on the relaxation behavior of pseudomorphic Si1−xGex buffer layers on Si (100) substrates

The influence of He implantation and annealing on the relaxation of Si0.7Ge0.3 layers on Si (100) substrates is investigated. Proper choice of the implantation energy results in a narrow defect band ≈100 nm underneath the substrate/epilayer interface. During annealing at 700–1000u200a°C, He-filled bubbles are created, which act as sources for misfit dislocations. Efficient annihilation of the threading dislocations is theoretically predicted, if a certain He bubble density with respect to the buffer layer thickness is maintained. The variation of the implantation dose and the annealing conditions changes density and size of spherical He bubbles, resulting in characteristic differences of the dislocation structure. Si1−xGex layers with Ge fractions up to 30 at.u200a% relax the initial strain by 70% at an implantation dose of 2×1016u2009cm−2 and an annealing temperature as low as 850u200a°C. Simultaneously, a low threading dislocation density of 107u2009cm−2 is achieved. The strain relaxation mechanism in the presence of He fi...

Schottky barrier height modulation using dopant segregation in Schottky-barrier SOI-MOSFETs

The effect of dopant segregation (DS) on the electrical behavior of silicon-on-insulator Schottky barrier MOSFETs (SB-MOSFETs) is investigated. Ion implantation with arsenic and boron and subsequent silicidation is used to create highly n- and p-doped interface layers at the silicide-silicon interface. As a result, a strong band bending occurs at the silicide-silicon interface giving rise to a lowering of the effective Schottky barrier height. In turn, an increased electron as well as hole injection into the channel leads to improvements of the off- and on-state of the SB-MOSFETs. Using dopant segregation n-type as well as p-type SB-MOSFETs with nickel silicide source/drain electrodes have been fabricated exhibiting an inverse sub-threshold slope close to the thermal limit and showing one order of magnitude higher on-currents if compared to SB-MOSFETs without DS. In essence, the use of dopant segregation allows the fabrication of high performance Schottky barrier MOSFETs.

Effective Schottky barrier lowering in silicon-on-insulator Schottky-barrier metal-oxide-semiconductor field-effect transistors using dopant segregation

We present an investigation of the use of dopant segregation in Schottky-barrier metal-oxide-semiconductor field-effect transistors on silicon-on-insulator. Experimental results on devices with fully nickel silicided source and drain contacts show that arsenic segregation during silicidation leads to strongly improved device characteristics due to a strong conduction/valence band bending at the contact interface induced by a very thin, highly doped silicon layer formed during the silicidation. With simulations, we study the effect of varying silicon-on-insulator and gate oxide thicknesses on the performance of Schottky-barrier devices with dopant segregation. It is shown that due to the improved electrostatic gate control, a combination of both ultrathin silicon bodies and gate oxides with dopant segregation yields even further improved device characteristics greatly relaxing the need for low Schottky barrier materials in order to realize high-performance Schottky-barrier transistors.

Gadolinium scandate thin films as an alternative gate dielectric prepared by electron beam evaporation

Gadolinium scandate thin films deposited on silicon substrates using electron beam evaporation were investigated. Measurements with Rutherford backscattering spectrometry, high temperature x-ray diffraction, x-ray reflectometry, transmission electron microscopy, and atomic force microscopy were performed. A stoichiometric transfer of material from the source to the substrate in high vacuum could be demonstrated. Homogeneous, amorphous, and smooth films (root mean square surface roughness <1A) stable up to 1000°C were obtained. Electrical characterization of capacitor stacks revealed a dielectric constant of ≈23, C-V curves with small hysteresises and low leakage current densities (770μA∕cm2 for a capacitance equivalent thickness of 1.5nm).

Tensely strained GeSn alloys as optical gain media

This letter presents the epitaxial growth and characterization of a heterostructure for an electrically injected laser, based on a strained GeSn active well. The elastic strain within the GeSn well can be tuned from compressive to tensile by high quality large Sn content (Si)GeSn buffers. The optimum combination of tensile strain and Sn alloying softens the requirements upon indirect to direct bandgap transition. We theoretically discuss the strain-doping relation for maximum net gain in the GeSn active layer. Employing tensile strain of 0.5% enables reasonable high optical gain values for Ge0.94Sn0.06 and even without any n-type doping for Ge0.92Sn0.08.

Tensely strained silicon on SiGe produced by strain transfer

An approach for the controlled formation of thin strained silicon layers based on strain transfer in an epitaxial Si∕SiGe∕Si(100) heterostructure during the relaxation of the SiGe layer is established. He+ ion implantation and annealing is employed to initiate the relaxation process. The strain transfer between the two epilayers is explained as an inverse strain relaxation which we modeled in terms of the propagation of the dislocations through the layers. Effcient strain buildup in the Si top layer strongly depends on the Si top layer thickness and on the relaxation degree of the SiGe buffer. 100% strain transfer was observed up to a critical thickness of the strained silicon layer of 8nm for a 150nm relaxed Si0.74Ge0.26 buffer.

Improved Carrier Injection in Ultrathin-Body SOI Schottky-Barrier MOSFETs

The impact of the gate oxide and the silicon-on-insulator (SOI) body thickness on the electrical performance of SOI Schottky-barrier (SB) MOSFETs with fully nickel silicided source and drain contacts is experimentally investigated. The subthreshold swing S is extracted from the experimental data and serves as a measure for the carrier injection through the SBs. It is shown that decreasing the gate oxide and body thickness allows to strongly increase the carrier injection and hence, a significantly improved on-state of SB-MOSFETs can be obtained

Effects of annealing on the electrical and interfacial properties of amorphous lanthanum scandate high-κ films prepared by molecular beam deposition

Amorphous LaScO3 thin films were grown on (100) Si by molecular beam deposition and the effects of postdeposition thermal treatments on the film properties were studied after anneals in O2 or inert Ar atmosphere at 400 or 650u2009°C. Rutherford backscattering spectrometry, transmission electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy (XPS) were employed to investigate the samples. Capacitance-voltage and current-voltage measurements allowed their electrical characterization. Postdeposition annealing in O2 reduces hysteresis, flatband voltage, and also leakage current density. In contrast, films treated in Ar ambient revealed a different behavior. The observations were associated with the interface evolution as studied by XPS, which verify that an O2 atmosphere favors the formation of a SiO2-rich interface between the film and the Si substrate, while a La-Sc-silicate-like compound predominates in this region after treating the samples in Ar. Additionally, postdeposition annealing re...