We demonstrate a thermally stable titanium silicide/titanium nitride (TiSix/TiN) full metal gate (FMG) for dual-channel gate-first high-k/metal gate complementary metal-oxide-semiconductor technology. Unlike prior tungsten-based FMG, the simple TiSix/TiN gate electrode does not require any additional barrier layer preventing oxygen down-diffusion during high-temperature processing, as the TiSix itself blocks oxygen. With HfO2-based gate dielectrics and without any oxygen scavenging scheme, we thus demonstrate a capacitance-equivalent thickness in inversion (T-inv) of 1.11 nm, corresponding to an equivalent oxide thickness of similar to 0.7 nm. Silicon channel nFET and silicon germanium channel pFET parametrics are similar to those of control devices utilizing a conventional a-Si/TiN metal-inserted poly-Si stack (MIPS) gate, while providing superior gate sheet resistance. By supplanting MIPS with such an FMG, we anticipate that contacted gate pitch can be scaled aggressively via reduced gate height and borderless source/drain contacts.

In this study, we survey germanide formation and characterize Schottky-barrier properties for a number of representative metals on Ge (Al, Ag, Au, Er, Ni, Pd, Pt, Ta and Ti). It is found that the germanide formation characteristics (sequence of phase formation, kinetics, moving species) are similar to those of the corresponding silicides. The Schottky-barrier heights, however, are all similar and centered around 0.59 eV arida re relatively insensitive to the metallization.

As the complexity of global materials science challenges increases, so does the need for materials science and engineering literacy and career recruitment. Many funding agencies are addressing this by including requirements for achieving broader impacts (e.g., National Science Foundation grants, European Commission Framework), and resources have been created from a variety of sources to help. This article addresses the issue of how to translate materials science concepts into K–12 outreach activities, with an emphasis on how to use the human, physical, and information resources available. Researchers may best reach their outreach objectives by distilling content rather than diluting it, connecting on a human level, highlighting the true nature of science, not reinventing the wheel, being a role model, and having fun. Initiatives that support outreach efforts are referenced and include examples from the Materials Research Society.

The solid-phase epitaxial regrowth of a III–V compound semiconductor by a two-stage reaction between a two-layer metallization and a compound semiconductor substrate is described. The regrowth process begins with a low-temperature reaction between a metal M (e.g. Ni, Pd, or Pt) and a compound semiconductor substrate, AB, to produce an intermediate M, AB or MB, phase. A subsequent reaction at a higher temperature between an overlayer of Si, Ge, Al, or In and the intermediate phase results in the decomposition of the intermediate phase and the epitaxial regrowth of a layer of the compound semiconductor. This regrowth mechanism is verified experimentally for the specific case of the Si/Ni/GaAs system. Rutherford backscattering spectrometry and transmission electron microscopy data show that the ternary phase Nix GaAs, formed during the initial stage of the reaction, decomposes toNiSi and GaAs by reaction with the Si overlayer. The incorporation of the overlayer element into the regrown semiconductor layer is proposed as a mechanism to explain the formation of Ohmic contacts in Si/Pd/n-GaAs, In/Pd/n-GaAs, In/Pt/n-GaAs, and similar two-layer metallization systems on n-GaAs.

Understanding metal/semiconductor contacts is important for the fabrication of device structures. To date most studies have been aimed at understanding the metallurgical or the electrical properties. Directly measuring the impurity concentrations immediately beneath a contact rather than inferring it from electrical measurements has up until now been difficult. This paper describes a backside SIMS technique which not only demonstrates the ability of measuring doping concentrations close to a metal/semiconductor contact but also is capable of measuring the consumption of semiconductor material during a metal/semiconductor reaction. The sample preparation technique can be used to enable backside profiling using other profiling techniques such as Auger and x-ray photoelectron spectroscopy depth profiling, Rutherford backscattering, and backside electrical evaluation. The Ge/Pd/GaAs solid phase ohmic contact is used to demonstrate the technique.

The back interface of a solar cell is an important part of the device structure, providing several important functions: 1) reduces the effective surface recombination velocity, therefore raises both the short circuit current and Voc; 2) it may contain a high-low junction which adds it's own contribution to the Voc and Vmax; 3) provides a low resistance ohmic contact. An added optical effect includes reflectance of long wavelength light back into the semiconductor not absorbed on the first pass through the material. The most common back interface structure is a " back surface field" created by a high -low junction. Others include a passivated surface using dielectrics such as SiO2, SiN, or Al2O3, a floating junction inbetween localized contacts, and a local BSF where a h-l junction is present between passivated regions. This paper focuses on the contribution to Voc made by the h-l junction.

Strong n but weak p-carrier passivation was observed when Si- and Mg-implanted/annealed GaAs samples were exposed to a 2D plasma under identical conditions. Even though a discrete band of dislocation loops was present in both the samples, the 2D distribution in the two cases was remarkably different. In the Si-implanted sample the 2D followed the carrier distribution, whereas in the Mg-implanted sample it followed the distribution of dislocation loops. Phenomenological mechanisms of 2D interaction with dopants/dislocations in GaAs are postulated.

We have achieved solid phase epitaxy of thin amorphous Si layers on GaAs using in situ plasma processing and subsequent annealing. High-resolution transmission electron microscopy of the SiO2/Si/GaAs structure shows that a Si layer ≂20 Å thick epitaxially crystallizes on GaAs after annealing at ≂570 °C in N2. Metal-oxide-semiconductor capacitors fabricated on these structures confirm the high quality of these interfaces. By comparing a high- frequency (100 kHz) capacitance-voltage curve with a quasi-static one, interface state densities as low as 4×1012 eV−1/cm−2 were measured on both n- and p-type GaAs.

A backside secondary ion mass spectrometry (SIMS) technique is employed to examine seven distinctive metallic contacts on GaAs at various stages of formation. The contacts are formed on multilayered GaAs/AlGaAs structures grown by molecular beam epitaxy (MBE), each containing an AlGaAs etch-stop layer and AlGaAs marker layers for precise alignment of the SIMS depth profiles. After removal of the substrate, the contact structures are profiled from the backside to avoid depth resolution degradation, which results when sputtering through a nonuniform multilayered metallic contact. The seven contacts examined are TaSix, Au/Ge/Ni, Au/Ge/Pd, Ge/Pd, Si/Pd, In/Pd, and Si/Ni/Mg. The TaSix Schottky contact exhibits extensive interdiffusion. The Au/Ge/Ni contact reveals extensive GaAs consumption. Much less consumption occurs in the Au/Ge/Pd contact. The absence of Au in the Ge/Pd contact leads to an extremely abrupt contact interface, with the Ge concentration dropping by four orders of magnitude within ∼100 Å of the interface. The Si/Pd contact is similar, with evidence of a complex compound formation within 200 Å of the interface. An ∼200 Å InGaAs region is in evidence at the In/Pd contact interface. The Si/Ni/Mg p-type ohmic contact profiles illustrate the progressive development of NiSi with the Mg layer serving as a diffusion barrier. The results are supplemented by transmission electron microscopy (TEM), and compared to various models of ohmic contact formation.

A backside secondary ion mass spectrometry technique is employed to examine elemental redistribution in the Ge/Pd/GaAs ohmic contact as a function of annealing conditions. Dilute Al containing marker layers (Ga1−x Alx As) in the GaAs permit precise calibration and alignment of the elemental depth profiles. Double etch-stop thinning yields high depth resolution. The onset of ohmic behavior is found to occur when Ge is detected at the GaAs surface. Good ohmic behavior is observed when an interfacial layer of reacted Pd4GaAs is dispersed and complete coverage of Ge occurs. The Ge/GaAs interface is abrupt with the Ge concentration dropping by over three orders of magnitude within 100 Å. About 40 Å of GaAs is found to be consumed during the ohmic contact formation. Degradation of the ohmic contacts, as a result of further heat treatment, was found to correlate with Ge in-diffusion into the GaAs. The results place strict limitations on doping and heterointerface models of ohmic behavior for this contact.

Results of the interaction of 40-nm Pd films on chemically cleaned InP substrates at temperatures from 175 to 650°C are reported. Comparisons are made with previous results from studies of Pd thin-films on GaAs. For both systems, the reaction began upon deposition of the metal. Ternary phases were found after annealing at temperatures up to 250°C. At 450°C and higher, the PdIn or PdGa phase was dominant because of loss of volatile P or As. Possibilities for making ohmic contacts based on these systems are discussed.

Annealed Ge/Pd/n-GaAs samples utilizing substrates with superlattice marker layers have been analyzed using high resolution backside secondary ion mass spectrometry and cross-sectional transmission electron microscopy. Interfacial compositional and microstructural changes have been correlated with changes in contact resistivity. The onset of good ohmic behavior is correlated with the decomposition of an intermediate epitaxial Pd4(GaAs,Ge2) phase and solid-phase regrowth of Ge-incorporated GaAs followed by growth of a thin Ge epitaxial layer.

The temperature dependence of the contact resistance of the Ge/Pd and Si/Pd metalization scheme on n-GaAs was investigated. These two contact systems are based on solid-phase reactions, thus leading to nonspiking ohmic contacts to n-GaAs. The experimental results show that the ohmic behavior is likely due to both a highly doped surface n+ region and/or a small barrier at the interface. The origin of this small barrier and nonlinear current-voltage characteristics for certain samples are also discussed.

Specific contact resistivity ρc of planar Ge/Pd ohmic contacts to n-type AlxGa1−xAs is measured as a function of AlAs mole fraction x and anneal temperature Tann. The functional dependence of ρc on Tann is the same for all x, decreasing to a minimum at 275–325 °C. This indicates that the ohmic contact formation mechanism is independent of x(0≤x≤0.3) as verified by MeV Rutherford backscattering spectrometry and Read camera glancing angle x-ray diffraction. Decomposition of an epitaxial Pd-AlxGa1−xAs phase is correlated with the onset of ohmic behavior and may result in a thin solid phase regrown interfacial AlxGa1−xAs layer. An undoped 20 nm GaAs cap layer reduces ρc by about one order of magnitude. Ge/Pd contacts display greater dependence of ρc on x and much smoother surface morphology compared with those of standard Au-Ge-Ni contacts on AlxGa1−xAs (0≤x≤0.3).

Germanium is experiencing a resurgence of interest due to superior intrinsic properties and recently overcome technological limitations. This paper addresses the problem of Schottky barrier height control. The Fermi level of metal/Ge contacts is pinned at between 0.54 and 0.61 eV below the conduction-band edge, independent of the contacting metallization. We compare the modulation of effective barrier height by means of shallow ion implantation, epitaxial growth, and diffusion from a doped level to create a thin, highly doped interfacial region. Lowering of n-type contacts from 0.54 to 0.4 eV, at room temperature, and enhancement of p-type contacts from 0.09 to 0.23 eV, at 77 K, have been achieved. Experimental results are compared to computer model calculations.