This paper will review the effects of strain on the electronic and vibrational properties of semiconductors and semiconductor microstructures. Topics to be discussed include deformation potential theory for electronic states () and vibrational modes () of bulk material, polarization effects, the influence of strain (internal and external) on quantum states (band alignments, light-and heavy-hole splittings, polarization effects), piezoelectric effect, strain relaxation, etc. Also various measurement techniques will be mentioned. Selected examples of various phenomenon will be given, including some new and novel device applications.

We investigate the desorption and segregation rates of Indium atoms on fully strained InxGal-xAs surfaces and their dependence on the surface As-coverage. The results are obtained by measuring the desorption of As using reflection high energy electron diffraction. The desorption rate of As is sensitive to the interaction energies between the group III atoms and the As-atoms. A change in the surface Indium-fraction results in a corresponding change in the desorption behavior of the As-atoms. Information of the surface alloy concentration can thus be obtained. Using this technique we find that segregation and desorption of Indium atoms on strained InxGa1-xAs surfaces is reduced for As-covered 2x4 reconstructed surfaces. The desorption rate of Indium is found to increase with the proximity to an inverted InAs/InxGalxAs interface. In contrast, the normal interface consisting of an InxGal-xAs layer grown on InAs is not seen to influence the desorption rate. This results is attributed to growth related defects specific for the inverted interface.

Thermal stabilities of GaAs/InGaP and InGaP/(In)GaAs interfaces are investigated using InGaP/(In)GaAs/InGaP single quantum wells. Annealing is performed at a temperature range between 600 and 900 °C for 10 min. Positions and the full widths at half maximum (FWHM) of photoluminescence (PL) peaks are almost identical to those of as-grown ones up to 800 °C. Blue shifts of PL peaks and increased widths of their FWHM observed after 900 °C annealing are suppressed by shortening the annealing time to 0.1 sec. Annealing at 900 ‘C for 0.1 sec is sufficient to activate Si ions implanted into (In)GaAs layers. As a result, these thermal stabilities are able to provide high reliability and high performance of InGaP/(In)GaAs heterostructure MESFET ICs.

Quantum Hall effect and Shubnikov-de Haas oscillations in a 2D hole gas at a p-GaAs/Al0.5Ga0 5As (001) interface show, that under in-plane (110) uniaxial compression a redistribution of carriers between the two spin-splitted subbands of the ground heavy hole state takes place. At the maximal compression of 2.5 kbar the carrier density of the most populated subband is decreased by 18%, while the total carrier density remains almost unchanged. A decrease of the spin-splitting under the uniaxial compression is proposed.

We have found that the lateral dimension of InGaAs and GaAs multiple layers can be effectively controlled on non-( 111) V-grooved GaAs substrates by chemical beam epitaxy using triethylgallium and trimethylindium coupled with precracked arsine or unprecracked monoethylarsine. We suggest that this effect is due to the efficient migration of adatoms from (111) to non-(111) planes. This is an improved method which overcomes the difficulty that has been associated with the method of using only (111) V-grooves in which the lateral dimension is controlled by the differences in the growth rates between (111) and (100) planes. In case of InGaAs and GaAs epilayers, the anisotropy factors of growth rate were less than 0.1 at optimum growth temperature. Photoluminescence peak originated from InGaAs/GaAs quantum wire was significantly distinct from other peaks, suggesting an effective reduction of InGaAs lateral dimension.

Facet evolution and selective area epitaxy of GaAs/AIGaAs ridge and V-groove structure grown on non-planar GaAs(100) substrate by chemical beam epitaxy(CBE) have been investigated for nanostructure applications. To enhance the crystallographic selectivity and to study the new facet evolution on patterned substrate, GaAs and AlGaAs epilayer were grown by growth-interruption mode and continuous mode, respectively. High selectivity of GaAs layer was observed to depend on the various crystallographic planes even at low growth temperature. This was attributed to the efficient Ga surface migration and desorption during the growth-interruption periods. The growth-interruption method was found to be very efficient in improving the morphology of faceted surfaces. We demonstrated that the formation of (111) V-groove and (411) ridge GaAs structures which were surrounded by AlGaAs layer to show the potential implication of this method for the formation of quantum wires.

The Al0.13Ga0.87As epilayers were regrown by metalorganic chemical vapor deposition (MOCVD) on different AI0.26Ga0.74As substrate layers. It was found that the quality of regrown A10.13Ga0.87As layers were significantly improved when a Se-doped Al0 26Ga0.74As substrate was used. Electrochemical C-V profile showed that no oxide formation and impurity incorporation at the regwon interface. Low-temperature (14.9 K) photoluminescence showed that the full width of half maximum (FWHM) of the bound exciton peak is as low as 4.51 meV. We attributed this improvement to the Se-passivation effect at the surface of Se-doped A10.26Ga0.74As substrate-layers. Results show that Se will delay the formation of native oxide to achieve the better quality of regrown AlGaAs layers.

The first in situ layer-by-layer etching of AlAs(100) surfaces has been observed by using RHEED intensity oscillations technique and is contrasted with the results obtained for the etching of GaAs(100). The experiments were conducted by introducing the etchant, arsenic tribromide, directly into a conventional MBE chamber without the use of any carrier gas. RHEED intensity oscillations during the etching of AlAs are observed between 350 and 760°C indicating a continuous increase in the etching rate with temperatures, with no supply rate limiting conditions being reached. Conversely, oscillations from GaAs reveal a reaction rate limited region at low temperatures (≤500°C) and a supply rate limited region at higher temperature(>500°C). The maximum selectivity in the etching rates between GaAs and AlAs is obtained at 450°C (40:1). The selectivity, and the ability to monitor the layer-by-layer process by RHEED intensity oscillations is foreseen to be of great importance for more controlled fabrications of AlAs and GaAs heterointerfaces.

We report a kinetic analysis of low-temperature NiSi2-mediated crystallization of amorphous Si by in situ transmission electron microscopy. The initiation of crystallization by formation of crystalline Si on buried NiSi2 precipitates is shown to have an activation energy of 2.8±0.7eV. Crystallization of the amorphous Si via migrating precipitates of NiSi2 occurs with an activation energy of 2.0±0.2eV. The significance of these activation energies is discussed in terms of possible atomistic mechanisms of crystalline Si initiation and subsequent growth. Amorphous Si is reported to crystallize at temperatures as low as 450°C.

Pseudomorphic Gel-yCy and Sil-yCy alloy layers have been synthesized by solidsource molecular beam epitaxy on Si (001) substrates. High quality short-period Gel-y Cy/Si superlattice structures with a carbon content up to about 5 % are grown at low substrate temperature. The partial compensation of strain within Ge964C036 layers of 7 Å thickness improves the thermal stability against lattice relaxation, compared to pure Ge layers. Band-edge related photoluminescence is observed from pseudomorphic Sil-yCy/Si multiple quantum well structures at low temperature. The two predominant luminescence lines are attributed to no-phonon transitions and Si-Si TO phonon replicas of bound excitons confined within the Sil-yCy alloy quantum well layers. The tensile strain within the Sil-yCy layers shifts the twofold degenerate Δ(2) conduction band valley down in energy and is mainly responsible for the linear band gap reduction which is observed for increasing C content.

We present recent results on the properties of ordered group IV compounds containing carbon, silicon and germanium. Our calculations are done using a full-potential -linearized muffin-tin orbital (FP-LMTO) method within the local density approximation (LDA). Twenty-seven fully relaxed compounds represented by six different compound structures have been examined. With the exception of SiC, all compounds are found to be metastable. Two trends emerge: compounds that have carbon on a common sublattice are less unbound because of their relatively low strain, and carbon-germanium bonds are disfavored. Simple two-body (bond-length) and three-body (bond-angle) empirical fits to our first-principles results are not adequate to predict excess energies with sufficient accuracy to be reliably predictive for other structures. Some compounds have direct gaps. When carbon shares a sublattice with silicon or germanium, the large strain results in a narrowing of the band gap, and in some cases the compound is metallic. The most promising structures with the lowest excess energy contain carbon on one sublattice and do not lattice match to silicon, but match rather well to silicon carbide.

Semiconductor quantum wires and dots have been fabricated in GaAs/AlGaAs, CdTe/CdMnTe and Si/SiGe multiple quantum wells using electron beam patterning and reactive ion etching and studied by photoreflectance, photoluminescence and Raman scattering. It was found that the smaller the lateral size of the nanostructure, the smaller the fabrication induced residual strain. In all cases, the dominant strain component is found to be parallel to the sample growth direction, i.e., along the etched sidewalls of the etched wires and dots. The lateral confining potential is found to be quasi-parabolic for polar semiconductor systems. Possible ways of using and controlling the damage and residual strain in nanostructures are discussed in the context of device applications of nanostructures.

The strain induced by thermal oxidation in a cylindrical silicon (Si) structure has been studied by high resolution synchrotron x-ray diffraction. The strain in the structure studied is expected to display some of the features that exist in three-dimensional non-planar surfaces in electronic devices. The sample consisted of a 2-dimensional array, with period of 300nm, of approximately cylindrical pillars covered with a thin thermal oxide (thickness ∼6nm). These showed a tensile strain of 3.7×10-4 at room temperature. This strain can be relaxed elastically by chemical removal of the oxide. Process simulation indicates the importance of both the contribution due to interface stress during the oxide growth and stress due to differential thermal contraction during the cooldown. Significant differences exist between the strain in such cylindrical pillars and in a flat wafer.

Quantum well microdisk laser structures have been fabricated in the GaN/InGaN, GaAs/AlGaAs and GaAs/InGaP systems using a combination of ECR dry etching (Cl2/CH4/H2/Ar, BC13/Ar or CH4/H2/Ar plasma chemistries respectively) and subsequent wet chemical etching of a buffer layer underlying the quantum wells. While wet etchants such as HF/H2O and HCI/HNO3/H2O are employed for AlGaAs and InGaP, respectively, a new KOH-based solution has been developed for AlN which is completely selective over both GaN and InGaN. Typical mask materials include PR or SiNx, while the high surface recombination velocity of exposed AlGaAs (∼105cm·sec-1) requires encapsulation with ECR-CVD SiNx to stabilize the optical properties of the modulators.

We present a theoretical model for calculation of stress distributions in semiconductor nanostructures such as lattice-mismatched InGaAs/GaAs quantum well wires and dots. The model is based on a linear elastic deformation approximation, and assumes dislocation-free interfaces with an additional condition of continuous interatomic distance on the interfaces. The distributions of stress tensor components and the resulting effective potentials for electronhole pairs are calculated. The comparison of our model with the experimental data on the exciton spectra in free standing strained InGaAs/GaAs quantum well wires is also presented.

We have investigated quantum-confined Stark effect (QCSE) on GaAs and CdSe nanocrystals and the electric field effect on surface phonons of GaAs nanocrystals isolated in sapphire substrates. For a strongly quantum-confined system, GaAs quantum dots illustrated no exciton energy shift. When the excitons are weakly confined in CdSe, a ∼ 2 meV red-shift was observed. On the other hand, the results of the electric field effect on surface phonon are dramatic both phonon oscilator strength and freqnency. As the strength of the electric field increases, the total intensity of the surface phonon decreases. At the same time, an additional peak was also observed at 277 cm-1, which is about 3 cm-1 above the center frequency of the surface phonon mode of GaAs nanocrystals embedded in a sapphire host.

We study the stability range for a coherent interface between Ge quantum dots and an epitaxial Si shell. The critical radius at which coherency is lost is evaluated as a function of Si shell thickness and Ge nanocrystallite radius by comparing the energy of the system in the coherent and incoherent state. We find that the system is coherent up to a Ge nanocrystallite radius of about 100 Å, irrespective of the Si shell thickness. Nanocrystallites of radii larger than 270 Å lose coherency by the generation of perfect dislocation loops. In nanocrystallites of intermediate radii ( between 100 Å and 270 Å), the coherency is lost by the introduction of partial dislocation loops enclosing a stacking fault. As the shell thickness decreases, the critical radius increases.

We present evidence for the large increase of the band gap due to the quantum localization in nc-Si imbedded in a-SiO2 matrix, which is in agreement with the original theoretical calculations. This, together with additional experimental data explains the large red shift between the onset of the excitation spectra and the photoluminescence. This also provides strong support for the mechanism of the photoluminescence which originates from radiative centers either at the Si/SiO2 interface or within the SiO2 matrix. The strong decrease of the efficiency of the photoluminescence due to a decrease of the thickness of the a-SiO2 grain boundaries is shown and its origin discussed. Delocalization of the photogenerated charge carriers due to ultra thin a-SiO2 is excluded as the cause of this effect. Microwave absorption is used to study the effect of the grain boundaries on the localization and delocalization of photogenerated charge carriers in pure nc-Si together with concomitant phenomena observed in Raman scattering. Finally we show the strong decrease of the photoluminescence decay time to ≤ 500 ps due to molecular-like radiative centers which are formed in the nc-Si/SiO2 composites by appropriate doping.

Since bulk silicon does not emit light in the visible part of the spectrum, the discovery of strong visible luminescence from porous silicon has been quite surprising and has generated significant interest. This material differs from bulk silicon in that it consists of interconnected silicon nanostructures, having very large surface to volume ratios. The first emission mechanism proposed involved carrier recombination within quantum size silicon particles, but more recent work has shown that surface emission models are more likely. In this paper, an interfacial oxygen center luminescence model will be discussed, with supporting experimental data. A direct correlation between the presence of these centers and the red photoluminescence in both as-made and oxidized PoSi will also be presented.

Using PL, PLE, secondary ion mass spectroscopy (SIMS) and EPR investigations we show in this paper that two luminescence bands with different PL excitation spectra exist on the surface of silicon wires in PS.