Strained Si n -channel metal-oxide-semiconductor field-effect transistors formed on very thin SiGe relaxed layer fabricated by ion implantation technique Appl. Phys. Lett. 90, 202101 (2007); 10.1063/1.2739324 Asymmetric strain relaxation in patterned SiGe layers: A means to enhance carrier mobilities in Si cap layers Appl. Phys. Lett. 90, 032108 (2007); 10.1063/1.2431702High-quality strain-relaxed SiGe alloy grown on implanted silicon-on-insulator substrate Surface channel strained Si metal-oxide-semiconductor field-effect transistors ͑MOSFETs͒ are a leading contender for future high performance complementary metal-oxide-semiconductor ͑CMOS͒ applications. The carrier mobility enhancement of these devices is studied as a function of channel strain, and the saturation behavior for n-and p-channel devices is compared. Carrier mobility enhancements of up to 1.8 and 1.6 are achieved for n-and p-channel devices, respectively. The process stability of strained Si MOSFETs is also studied, and carrier mobility enhancement is shown to be robust after well implantation and virtual substrate planarization steps. The effects of high-temperature implant activation anneals are also studied. While no misfit dislocation introduction or strain relaxation is observed in these devices, increased interface state densities or alloy scattering due to Ge interdiffusion are shown to decrease mobility enhancements. Channel thickness effects are also examined for strained Si n-MOSFETs. Loss of carrier confinement severely limits the mobility of devices with the thinnest channels. Overall, surface channel strained Si MOSFETs are found to exhibit large carrier mobility enhancements over coprocessed bulk Si devices. This, combined with the high process stability exhibited by these devices, makes them superb candidates for future CMOS applications.

We have fabricated strained Ge channel ptype metal-oxide-semiconductor field-effect transistors (p-MOSFETs) on Si 0.3 Ge 0.7 virtual substrates. The poor interface between silicon dioxide (SiO 2) and the Ge channel was eliminated by capping the strained Ge layer with a relaxed, epitaxial silicon surface layer grown at 400ºC. Ge p-MOSFETs fabricated from this structure show a hole mobility enhancement of nearly 8 times that of co-processed bulk Si devices, and the Ge MOSFETs have a peak effective mobility of 1160 cm 2 /V-s. These MOSFETs demonstrate the possibility of creating a surface channel enhancement mode MOSFET with buried channellike transport characteristics.

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We report the behavior of the electrochemical capacitance for a variety of atomic junctions using ab initio methods. The capacitance can be classified according to the nature of conductance and shows a remarkable crossover from a quantum dominated regime to that of a classical-like geometric behavior. Clear anomalies arise due to a finite density of states of the atomic junction as well as the role played by the atomic valence orbitals. The results suggest several experiments to study contributions due to quantum effects and the atomic degree of freedom. [S0031-9007(98)06031-1] PACS numbers: 73.40.Cg, 61.16.Ch, 61.43.BnFor a very small conductor in which quantum effects play a role, it is not difficult to imagine that capacitance of the conductor may behave differently from the familiar classical case. For a small conductor its discrete nature of electron energy levels can be important, and the quantum correction due to the finite density of states (DOS) of the plates is known as the quantum capacitance [1,2]. For a microscopic sized conductor in which quantum coherence is maintained, one must consider the role played by the leads which connect the conductor to the outside world. One also needs to consider the finite screening length of the interacting electrons when it is not small compared with the system size. At these very small length scales, the relevant capacitance is the electrochemical capacitance C ϵ edQ͞dm, which is a quantity depending on the electronic properties of the conductor [2].Capacitance plays a central role in many phenomena such as the Coulomb blockade, and it is very important for several experimental techniques. However, there have been no quantitative predictions of capacitance for microscopic systems. Thus, we do not yet know its dependence on the atomic valence orbitals, the environment (e.g., the leads), and the shape, size, and other properties of a nanosystem. The purpose of this work is to make this connection by theoretically investigating capacitance of atomic junctions. In particular we shall study junctions formed by a small cluster of atoms, shown in the right panel of Fig. 1, where the clusters are sandwiched in between two metallic leads. We emphasize small system size where quantum effects are dominant and we answer a number of very relevant questions: (i) What is the value of the capacitance of these atomic junctions? (ii) What is the effect of atomic orbitals? (iii) How do we characterize the behavior of the capacitance? (iv) For the tip-substrate system familiar to scanning tunneling microscopy (STM), what is the C C͑d͒? Although atomic nanosystems are of great current interest [3], these fundamental questions, which are important to ac transport, have not been addressed. It is clear that capacitance and many other mechanical and electrical properties of atomic junctions can be obtained only from detailed first principle analysis [4]. This will be our approach.The theoretical analysis consists of four steps. First, we determine the atomic cluster shape by extensive quant...