Using nonlocal empirical pseudopotentials, we compute the band structure and shear deformation potentials of strained Si, Ge, and SiGe alloys. Fitting the theoretical results to experimental data on the phonon‐limited carrier mobilities in bulk Si and Ge, the dilatation deformation potential Ξd is found to be 1.1 eV for the Si Δ minima, −4.4 eV for the Ge L minima, corresponding to a value for the valence band dilatation deformation potential a of approximately 2 eV for both Si and Ge. The optical deformation potential d0 is found to be 41.45 and 41.75 eV for Si and Ge, respectively. Carrier mobilities in strained Si and Ge are then evaluated. The results show a large enhancement of the hole mobility for both tensile and compressive strain along the [001] direction, but only a modest enhancement (approximately 60%) of the electron mobility for tensile biaxial strain in Si. Finally, from a fit to carrier mobilities in relaxed SiGe alloys, the effective alloy scattering potential is determined to be about 0...

Band structure, deformation potentials, and carrier mobility in strained Si, Ge, and SiGe alloys

This article reviews the history and current progress in high-mobility strained Si, SiGe, and Ge channel metal-oxide-semiconductor field-effect transistors (MOSFETs). We start by providing a chronological overview of important milestones and discoveries that have allowed heterostructures grown on Si substrates to transition from purely academic research in the 1980’s and 1990’s to the commercial development that is taking place today. We next provide a topical review of the various types of strain-engineered MOSFETs that can be integrated onto relaxed Si1−xGex, including surface-channel strained Si n- and p-MOSFETs, as well as double-heterostructure MOSFETs which combine a strained Si surface channel with a Ge-rich buried channel. In all cases, we will focus on the connections between layer structure, band structure, and MOS mobility characteristics. Although the surface and starting substrate are composed of pure Si, the use of strained Si still creates new challenges, and we shall also review the litera...

Strained Si, SiGe, and Ge channels for high-mobility metal-oxide-semiconductor field-effect transistors

A leading-edge 90-nm technology with 1.2-nm physical gate oxide, 45-nm gate length, strained silicon, NiSi, seven layers of Cu interconnects, and low-/spl kappa/ CDO for high-performance dense logic is presented. Strained silicon is used to increase saturated n-type and p-type metal-oxide-semiconductor field-effect transistors (MOSFETs) drive currents by 10% and 25%, respectively. Using selective epitaxial Si/sub 1-x/Ge/sub x/ in the source and drain regions, longitudinal uniaxial compressive stress is introduced into the p-type MOSEFT to increase hole mobility by >50%. A tensile silicon nitride-capping layer is used to introduce tensile strain into the n-type MOSFET and enhance electron mobility by 20%. Unlike all past strained-Si work, the hole mobility enhancement in this paper is present at large vertical electric fields in nanoscale transistors making this strain technique useful for advanced logic technologies. Furthermore, using piezoresistance coefficients it is shown that significantly less strain (/spl sim/5 /spl times/) is needed for a given PMOS mobility enhancement when applied via longitudinal uniaxial compression versus in-plane biaxial tension using the conventional Si/sub 1-x/Ge/sub x/ substrate approach.

A 90-nm logic technology featuring strained-silicon

This paper focuses on approaches to continuing CMOS scaling by introducing new device structures and new materials. Starting from an analysis of the sources of improvements in device performance, we present technology options for achieving these performance enhancements. These options include high-dielectric-constant (high-k) gate dielectric, metal gate electrode, double-gate FET, and strained-silicon FET. Nanotechnology is examined in the context of continuing the progress in electronic systems enabled by silicon microelectronics technology. The carbon nanotube field-effect transistor is examined as an example of the evaluation process required to identify suitable nanotechnologies for such purposes.

Beyond the conventional transistor

A detailed theoretical picture is given for the physics of strain effects in bulk semiconductors and surface Si, Ge, and III–V channel metal-oxide-semiconductor field-effect transistors. For the technologically important in-plane biaxial and longitudinal uniaxial stress, changes in energy band splitting and warping, effective mass, and scattering are investigated by symmetry, tight-binding, and k⋅p methods. The results show both types of stress split the Si conduction band while only longitudinal uniaxial stress along ⟨110⟩ splits the Ge conduction band. The longitudinal uniaxial stress warps the conduction band in all semiconductors. The physics of the strain altered valence bands for Si, Ge, and III–V semiconductors are shown to be similar although the strain enhancement of hole mobility is largest for longitudinal uniaxial compression in ⟨110⟩ channel devices and channel materials with substantial differences between heavy and light hole masses such as Ge and GaAs. Furthermore, for all these materials,...

Physics of strain effects in semiconductors and metal-oxide-semiconductor field-effect transistors

An enhancement‐mode p‐channel metal‐oxide‐semiconductor field‐effect transistor (PMOSFET) is fabricated on a strained Si layer for the first time. A biaxial strain in a thin Si layer is produced by pseudomorphically growing this layer on a Ge0.25Si0.75 buffer layer which is grown on a Si substrate. At higher magnitude of gate bias, channel mobility of a strained Si PMOSFET has been found to be 50% higher than that of an identically processed conventional Si PMOSFET.

High-mobility p-channel metal-oxide-semiconductor field-effect transistor on strained Si

Strain Hamiltonian and k⋅p theory are employed to calculate low‐field hole mobility of strained Si layers on (100)Si1−xGex substrate. Nonparabolicity and the warped nature of the valence bands are included. At room temperature, in‐plane hole mobilities of strained Si are found to be 1103 and 2747 cm 2 V−1 s−1 for x equal to 0.1 and 0.2, respectively. These hole mobilities are, respectively, 2.4 and 6 times higher than that of bulk Si. This improvement in the mobility results is mainly due to the large splitting energy between the occupied light‐hole band and the empty heavy‐hole band and smaller effective mass. The effect of p‐type doping on mobility is also presented.

Low‐field hole mobility of strained Si on (100) Si1−xGex substrate

Intense photoluminescence (PL) was observed from a new class of Si‐based quantum well structures (QWs), that is, neighboring confinement structure (NCS). NCS consists of a single pair of tensile‐strained‐Si layer and a compressive‐strained Si1−yGey layer sandwiched by completely relaxed Si1−xGex ( layers. In spite of the indirect band structure in real and k spaces, radiative recombination was enhanced compared with not only type‐II strained‐Si/relaxed‐Si1−xGex QWs but also type‐I strained‐Si1−yGey/relaxed‐Si1−xGex QWs. PL without phonon participation was found to dominate the spectrum possibly due to the effective carrier confinement for both electrons and holes. Quantum confinement effect was clearly observed by varying the well width, showing that the expected band alignment is realized.

Enhancement of radiative recombination in Si‐based quantum wells with neighboring confinement structure

A high‐quality completely relaxed SiGe buffer layer is grown on Si(100) by gas‐source molecular‐beam epitaxy. A pseudomorphic Si layer is grown on this relaxed SiGe buffer to form SiGe/strained‐Si/SiGe type‐II (staggered) quantum wells. Intense band‐edge photoluminescence is observed from these quantum wells for the first time. The quantum confinement effect in SiGe/strained‐Si/SiGe type‐II quantum wells is demonstrated from the systematic shift of photoluminescence energy peaks with the width of the quantum well. Transitions from the strained‐Si quantum well are identified as radiative recombination of excitons, which are confined into the quantum well.

Band-edge photoluminescence of SiGe/strained-Si/SiGe type-II quantum wells on Si(100)

An enhancement-mode high-mobility p-channel metal-oxide-semiconductor field-effect-transistor (MOSFET) is fabricated on strained Si layer for the first time. A biaxially strained thin Si layer is pseudomorphically grown on a relaxed GeSi buffer on Si substrate by molecular beam epitaxy (MBE). MOSFETs are fabricated using conventional Si process technology. It is found that low-field channel mobility of PMOSFET on strained Si is 50% higher than that of PMOSFET on bulk Si.

D. K. Nayak

Papers

High-mobility p-channel metal-oxide-semiconductor field-effect transistor on strained Si

Low‐field hole mobility of strained Si on (100) Si1−xGex substrate

Enhancement of radiative recombination in Si‐based quantum wells with neighboring confinement structure

Band-edge photoluminescence of SiGe/strained-Si/SiGe type-II quantum wells on Si(100)

High-Mobility p-Channel Metal-Oxide-Semiconductor Field-Effect-Transistor on Strained Si