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Maskless pendeo-epitaxy involves the lateral and vertical growth of cantilevered "wings" of material from the sidewalls of unmasked etched forms. Gallium Nitride films grown at 1020°C via metalorganic vapor phase epitaxy on GaN/AlN/6H-SiC(0001) substrates previously etched to form -oriented stripes exhibited similar vertical [0001] and lateral growth rates, as shown by cross-sectional scanning electron microscopy. Increasing the temperature increased the growth rate in the latter direction due to the higher thermal stability of the surface. The surface was atomically smooth under all growth conditions with a root mean square (RMS)=0.17 nm. High resolution X-ray diffraction and atomic force microscopy of the pendeo-epitaxial films confirmed transmission electron microscopy results regarding the significant reduction in dislocation density in the wings. This result is important for the properties of both optoelectronic and microelectronic devices fabricated in III-Nitride structures. Measurement of strain indicated that the wing material is crystallographically relaxed as evidenced by the increase in the c-axis lattice parameter and the upward shift of the E2 Raman line frequency. A strong D°X peak at 3.466 eV was also measured in the wing material. However, tilting of the wings of ≤0.15° occurred due to the tensile stresses in the stripes induced by the mismatch in the coefficients of thermal expansion between the GaN and the underlying substrate.

Gallium nitride films of increasing thickness have been grown on either AlN or AlGaN substrates. The state of stress of these biaxially stressed layers gradually changed from compression to tension with regard to both their average strain and their local strain along the [0001] growth direction. The components of both the compressive and tensile stresses are caused by the mismatch in lattice parameters between the GaN and the buffer layer and the mismatch in the coefficients of thermal expansion between GaN and SiC, respectively. The compressive stress is partially relieved within the first 20 nm in the GaN film grown on the AlN buffer layer. The relief of the remaining stress follows an exponential dependence on the thickness of the GaN layer with values for the characteristic decay length of 0.24 μm and 0.64 μm for the AlN and AlGaN buffer layer, respectively. The relaxation mechanism is discussed in terms of the formation of misfit dislocations via surface undulations.

The cracking of GaN films and the associated cracking of substrates are described. The geometry, structure, and evolution of fracture demonstrate that GaN films crack under tensile stress during growth and are subsequently overgrown and partially healed. The film cracks channel along the (1010)_GaN planes and also extend a distance of ~5 μm into the sapphire substrate. These incipient cracks in the substrate form a set of initial flaws that leads to complete fracture through the sapphire during cooling for sufficiently thick films. Each stage of this cracking behavior is well described by a fracture mechanics model that delineates a series of critical thicknesses for the onset of cracking that are functions of the film and substrate stresses, thicknesses, and elastic properties. Similar cracking behavior is found to occur independently of the choice of substrate between sapphire and SiC and is traced to a tensile stress generation mechanism early in the growth process, such as that provided by island coalescence. Cracking is the dominant stress relief mechanism, as opposed to dislocation generation or diffusion, because of the island growth mode and because of optimized growth temperatures at or below the brittle-to-ductile transition. Lateral epitaxial overgrowth (LEO) of GaN is shown to minimize substrate fracture even though film cracking remains unaffected. This effect explained in terms of the limits placed on the initial extent of insipient substrate cracks due to the LEO geometry.

Ultra-thin body Double Gate MOS structures with strained silicon are investigated by solving the 1-D Schrödinger and Poisson equations, with open boundaries conditions on the wave functions in the gate electrodes. The electrostatics of this device architecture and its dependence on the amount of strain and on the thickness of the silicon layer is analyzed in terms of subband structure, subband population, carrier distribution within the strained-silicon layer, charge-voltage characteristics and gate tunneling current.

SOI technology offers ample room for scaling, performance improvement, and innovations. The current status is reviewed by focusing on several technological options for boosting the transport properties in SOI MOSFETs. The impact of series resistance, high-K dielectrics, and metal gate in advanced transistors is discussed. Carrier mobility measurements as a function of channel length and temperature reveal the beneficial effect of strain, mitigated however by various types of defects. The experimental data is exclusively collected from state-of-the-art, ultrathin body, fully depleted MOSFETs. Simple models are presented to clarify the mobility behavior.

GaN-based pseudomorphic heterostructures with their demonstrated superior thermal performance suggest an alternative to the standard GaAs-based technology to realize high power lasing at THz frequencies. A larger electron effective mass in GaN based system results in the energy levels lying deeper within the quantum well compared to its GaAs counterpart resulting in longer carrier lifetimes assisting transitions required for THz radiation while reducing tunneling current. However, the presence of spontaneous and piezoelectric polarization and dependence of bandgap and band offsets on structural and bias induced strain reduces carrier lifetime.

We have investigated the residual in-plane strain and width of the surface misfit dislocation free zone in linearly-graded GaAs_1-yP_y metamorphic buffer layers as approximated by a finite number of sublayers. For this purpose we have developed an electric circuit model approach for the equilibrium analysis of these structures, in which each sublayer may be represented by an analogous configuration involving a current source, a resistor, a voltage source, and an ideal diode. The resulting node voltages in the analogous electric circuit correspond to the equilibrium strains in the original epitaxial structure. Utilizing this new approach, we show that the residual surface strain in linearly-graded epitaxial structures increases monotonically with grading coefficient as well as the number of sublayers, and is strongly dependent on the width of the misfit dislocation free zone, which diminishes with an increasing grading coefficient.

Chirped superlattices are of interest as buffer layers in metamorphic semiconductor device structures, because they can combine the mismatch accommodating properties of compositionally-graded layers with the dislocation filtering properties of superlattices. Important practical aspects of the chirped superlattice as a buffer layer are the surface strain and surface in-plane lattice constant. In this work two basic types of InGaAs/GaAs chirped superlattice buffers have been studied. In design I (composition modulated), the average composition is varied by modulating the composition of one of the two layers in the superlattice period, but the individual layer thicknesses were fixed. In design II (thickness modulated), the individual layer thicknesses were modulated, but the compositions were fixed. In this paper the surface strain and surface in-plane lattice constant for these chirped superlattices are presented as functions of the top composition and period for each of these basic designs.

Halide perovskite materials such as FAPbI3 are of great interest for photovoltaic applications and could replace silicon cells if problems of chemical instability, strain and crystal defects are solved. In this paper we present a preliminary modeling study of lattice relaxation in epitaxial FAPbI₃ on MAPbCl_xBr_3-x (001).