We investigate the electronic structure and stability of GaAs1–xNx alloys for several compositions, using state-of-the-art first-principles total-energy calculations. We consider several ordered structures, and in addition we address the case of low-dimensional structures, such as zero-dimensional point defects (NAs in GaAs). Our results reveal two rem ark-able features of this alloy system: (i) a very large bowing of the band gap (the system may even become metallic for compositions around x = 0.5) and (ii) a very limited miscibility. Both properties are related to a distinctive property of this alloy system: a more than 20% lattice mismatch between GaAs and GaN.

We have studied the growth of lattice mismatched semiconductors through the association of the Monte Carlo technique and the Valence Force Field (VFF) approximation. The Monte Carlo technique monitors the atomic motion in the deposited layer using the Arrhenius law and taking into account the impingment of atoms from the gas phase, intralayer and interlayer migrations of atoms and evaporation from the surface. The VFF approximation is used as an energy model to determine the local strain and stress inside the deposited layer by minimizing the total energy. This is performed after each single atomic motion. The strain is assumed to enhance the atomic motion by lowering the activation energy barrier related to the particular event. Results concerning the case of large lattice mismatches are presented. It is observed that the growing surface becomes rapidly rough, showing grooves with (111) facets. The strain relaxation occurs as a result of this roughening and allows the determination of the critical thickness. At higher lattice mismatches, it is seen that the layer orientation changes from(100) to (111) from the beginning.

Lattice mismatch associated with heteroepitaxy imposes a significant limitation on the epitaxial compatibility between overlayer and substrate. In lattice mismatched systems the misfit may be accommodated to some extent by strain. However, in order to maintain misfit strain and avoid dislocation generation the epitaxial layer must not exceed a critical thickness. Some success has been reported in avoiding damaged epitaxial layers with thicknesses greater than the critical thickness by overgrowing on patterned or rough surfaces. For the case of Si, surface roughening by energetic Ar+ bombardment as a pre-growth roughening treatment is discussed and assessed. Evolution of surface features as a function of initial substrate treatment, ion accelerating potential, and the duration of bombardment are presented. Stability of the surface features generated by bombardment for typical overgrowth conditions was tested to assess feasibility of this technique for Si heteroepitaxy.

We have investigated the effects of substrate misorientation direction on strain relaxation at InGaAs/GaAs(001) interfaces. Calculations of the shear stresses due to the misfit strain, resolved on the glide plane in the glide direction, suggest that the dislocation glide force and the activation energy for dislocation nucleation are essentially identical for the α and β slip systems. However, experimental results indicate that asymmetries in strain relaxation are sensitive to A-type misorientation and/or step-edge densities. Thus, a dislocation nucleation source or glide velocities sensitive to step densities or local roughness may explain these results.

The strain induced by the thermal mismatch in Pbl−xSnxSe and other IV–VI compound layers on Si(111)-substrates relaxes by glide of dislocations in the main <110> {001}-glide system. The glide planes are arranged with 3-fold symmetry and inclined to the (111)-surface. Despite a high threading dislocation density (> 107 cm−2) in these heavily lattice mismatched structures, the misfit dislocations move easily even at cryogenic temperatures and after many temperature cycles between RT and 77K. The cumulative plastic deformation after these cycles is up to 500%! Despite a pronounced deformation hardening occurs, the structural quality of the layer is only slightly adversely affected as regards additional threading dislocations created. The interaction probability between these dislocations is estimated to be about 10−5.

We show that an activation energy barrier exists to the formation of wavy step edges due to stress-driven 2D instability. The barrier height and the barrier width depend sensitively on the surface stress anisotropy and step free energy. The large misfit strain of Ge films significantly reduces the barrier by lowering the SB step energy, inducing SA steps to undergo a triangular instability even during low temperature growth of Ge on Si(100). The step instability results in a novel arrangement of stress domains, and the interaction between the domains causes a spatial variation of surface strain with a surprisingly large influence on the energy barrier for island nucleation. Calculations indicate a dramatic enhancement in the nucleation of 3D islands at the apex regions of triangular steps, in good agreement with our experimental measurements.

The evolution of defects in SiGe/Si strained layer superlattices (SLS)-with thickness and composition near the critical thickness -was investigated. The structures were grown on 2° miscut (001) substrates by ultrahigh vacuum chemical vapor deposition. The samples were then annealed between 700 °C and 900 °C. After annealing, the satellite peak intensity from double axis diffraction decreased and triple axis diffraction showed that this decreased intensity was due to increased mosaic structure. Interestingly, for some of the annealed samples, the (004) reciprocal space maps showed an asymmetric mosaic spread, indicating a preferential tilt. This result stems from a preferential propagation of certain types of misfit dislocations due to the substrate miscut.

The formation of amorphous interlayers (a–interlayers) by solid–state diffusion in ultrahigh vacuum deposited polycrystalline Ti thin film on germanium and Sil-xGex alloys grown on (001)Si has been investigated by transmission electron microscopy and Auger electron spectroscopy.

Amorphous interlayers, less than 2 nm in thickness, were observed to form in all as–deposited samples. The growth of a–interlayers was found to vary non–monotonically with the composition of Si–Ge alloys in annealed samples. On the other hand, the formation temperature of crystalline phase was found to decrease with the Ge content. The results are compared with that of the Ti/Si system. The formation mechanism are discussed in terms of thermodynamic and kinetic factors.

Lateral compositional graded (GaAs)1-x(Si2)x alloys were deposited on GaAs substrates in a III-V molecular beam epitaxy (MBE) chamber equipped with a electron-beam Si evaporation source. Single crystal GaAs-Si alloys were formed when the deposition temperature was 600°C or higher. The alloys were characterized by Energy Dispersive X-ray Spectroscopy (EDS), Raman scattering measurement and cross-sectional Transmission Electron Microscopy (XTEM). Dislocation-free (GaAs)1-x(Si2)x films of up to x = 0.07 were deposited. For alloys with x between 0.15 < < 0.25, the morphology deteriorates and a high density of stacking faults and micro-twins were observed.

In this paper, we calculated theoretically the strain distribution and the critical thickness of the SiGe epilayers on Si(100) mesa structural substrates by considering the effect of the compliance of substrates, along with the effect of the limited area, and found that the compliance of substrates was relevant not only to its thickness, but also to their lateral size. The introduction of substrate compliance significantly reduced the total strain energy in the epilayers, and increased the critical thickness. That approach was realized by growth on the mesa substrates. The TEM observations confirmed the results of calculations.

A new type of graded buffer layer, called graded short-period superlattice (GSSL) buffer layer, is proposed, and its effect on improving the material quality is investigated by comparing the qualities of 50-period InGaP/GaP multiple quantum wells (MQWs) grown on top of it and on a linearly graded (LG) buffer layer. Unlike the linearly graded buffer layer, in which the In composition is changed 1% per step size with a constant composition InGaP, the new buffer uses InGaP/GaP short-period superlattice within each step, while maintaining the average In composition of the short-period superlattice being changed the same amount per step size. Characterization of these structures by high-resolution X-ray diffraction and low-temperature photoluminescence indicates that, while the MQWs grown on a GSSL buffer show comparable structural properties as compared with those on an LG buffer, they exhibit higher PL intensity and narrower PL line width.

We investigated the effect of substrate inclination and direction on the structural properties of an InGaAs linearly compositionally graded buffer layer with a AlGaAs/InGaAs superlattice grown by molecular beam epitaxy on 2° offcut GaAs substrates. Reciprocal space maps were used to determine the relaxation and tilt of the buffer layer and superlattice with respect to each other and to the substrate. From (004) reciprocal space maps, a linear relationship between tilt and In mole fraction was observed for the buffer layer. This tilt was greatly reduced near the top of the buffer which was found to be completely strained. Interestingly, the tilt along a <110> direction was greater than that observed along the miscut axis. This may be due to the miscut axis not being parallel to a low index plane. Reciprocal space maps of asymmetric diffraction planes were used to determine the relaxation of the buffer layer as a function of In mole fraction. Along a <110> direction in which no tilt was seen in the (004), the majority of the buffer layer was found to be completely relaxed. However, the top of the buffer layer was found to be completely strained, corresponding to a denuded zone observed in cross section transmission electron microscopy.

Antimony was used as a surfactant during solid-source molecular beam epitaxy of AIGaAs layers. A steady-state surface-segregated population of Sb was maintained at the AIGaAs growth surface by providing a continuous Sb2 flux to compensate for loss due to thermal desorption. Above ∼ 650 °C, the incorporation rate of Sb was negligible, thereby allowing the deposition of AlGaAs layers despite the presence of Sb at the surface. A significant improvement in the optical quality of Al0.24Ga0 76As layers was observed by photoluminescence. In addition, extended reflection high energy electron diffraction oscillations and a reduction in Al0.24Ga0.76As surface roughness was observed when Sb was employed as a surfactant.

In this paper we have studied the photoemission from quantum wells (QW), quantum wells wires (QWWs) and quantum dots (QDs) of quantum confined strained III–V compounds on the basis of a newly formulated electron dispersion law. It is found taking such quantum confined Hg1–xCdxTe and In1–xGaxAsyP1–y lattice matched InP as examples that the photoemission increases with increasing energy of the incident photons in a ladder like manner and also exhibits oscillatory dependences with changing electron concentration and film thickness respectively for all types quantum confinement. The photoemitted current is greatest in strained QDs and least in unstrained QWs. In addition the theoretical results are in agreement with the experimental datas as given elsewhere.

Using lithography, and selective etching the Si1-xGex/Si multiple quantum well wires are fabricated. The characteristics of the selective chemical etching of Si1-xGex and Si are investigated, and high-performance etchants are developed. The etchant composed of HF:NH4F:H202:NH4OH is used for the etching of the epitaxial Si1-xGex films, the selectivity is better than 250 for Si0.76Ge0.24, and increases with the increase of the mole fraction x of Ge. Another etchant composed of NH4NO3:NH4OH is used for the etching of Si, the selectivity is higher than 1000 ( x ≥ 0.1 ). A preliminary photoluminescence (PL) result obtained from the Si0.76Ge0.24 multiple quantum well wires is presented. As the linewidth of the wires is reduced down to 50 nm, an intense complicated PL spectrum in the wavelength range of 500∼800 nm is observed at liquid nitrogen temperature. The origin of such spectrum is unclear.

The tilt of epilayer lattice planes in (100) zinc blende lattice-mismatched heterostructures is calculated numerically using the Dodson-Tsao plastic relaxation model. Tilt is calculated as a function of growth temperature, initial defect density and substrate miscut angle. The results are explained by looking at the time evolution of the excess stresses of the opposing slip systems during strain relaxation.

A new method is presented for the measurement of the radii of curvature R of semiconductor wafers using the magic-mirror (Makyoh) technique. A flat mirror is placed beneath the sample, thus a second, “contour” image of the sample is formed beside the Makyoh image. From the ratio of the two image sizes, R can be determined using a set of reference curved mirrors. Model calculations show good agreement with the results. Other examples of assessing of the flatness of semiconductor samples are presented as well.

In this paper an attempt is made to study the electronic contribution to the elastic constants of strained III-V materials under high magnetic fields on the basis of k.p theory. It is found taking strained Hgi - x CdxTe and Ini - xGaxAsyPi-y lattice matched InP as examples that they increase with increasing doping and oscillate with inverse magnetic field respectively. The strain enhances the numerical values of the elastic constants. The theoretical formulation is in quantitative agreement with the suggested experimental method of determining the above contributions for degenerate materials having arbitrary dispersion laws. In addition, the well-known results for strain free wide gap materials in the absence of magnetic field have been obtained from our generalized analysis under certain limiting conditions.

The temperature dependence of the cathodoluminescence (CL) originating from In0.21Ga0.79As/GaAs multiple quantum wells has been studied between 86 and 250 K. The CL intensity exhibits an Arrenhius-type dependence on temperature (T), characterized by two different activation energies. The spatial variations in activation energy caused by the presence of interfacial misfit dislocations is examined. The CL intensity dependence on temperature for T ≲ 150 K is controlled by thermally activated nonradiative recombination. For T ≳ 150 K the decrease in CL intensity is largely influenced by thermal re-emission of carriers out of the quantum wells.

Schottky diodes were fabricated by evaporating metal thin layers on p-Si1-xGex by cryogenic processing. The cryogenic processing, with substrate temperature cooled to as low as 77K (LT), has been successfully used to enhance metal/III-V semiconductor Schottky barrier height[1]. The electrical characteristics of the diodes were investigated by current-voltage (IV) and current-temperature (I-T) measurements. In order to study the effect of silicide formation on diode characteristics, furnace annealing was performed in nitrogen atmosphere at 450°C and 550°C, respectively. Two kinds of samples with gemanium composition x of 0.17 and 0.20 were used. The electrical characteristics showed the barrier height фB decreased with the increase of the gemanium composition. The annealing temperatures up till to 550°C did not affect the I-V characteristics at room temperature, however, the conduction mechanism showed obvious difference comparing to the as-deposited diodes by I-V-T analysis. For Pd as Schottky metal, very similar results were obtained for the LT as-deposited diodes and the ordinary room temperature (RT) deposited diodes after 550° annealing, they both showed thermionic emission dominated conduction mechanism.