It is demonstrated that the time required for strain transference during the postgrowth anneal of a SOI compliant substrate system is much too long to explain the observed reduction in dislocation density in the resulting microstructure. A mechanism by which misfit dislocation segments are drawn out of the system through viscous dissipation in the bonding layer is proposed and demonstrated to be consistent with observation. The mechanism is mtodeled in the context of elastic dislocation theory and linear viscoelasticity.

One critical issue in heteroepitaxial, lattice mismatched growth is the inevitable appearance of threading dislocations which reside in the relaxing film and degrade its semiconducting properties. It has been shown in previous work that threading dislocations interact with each other through a series of annihilation and fusion reactions to decrease their density as the film thickness increases and follow a 1/h decay, where h is the film thickness. A characteristic reaction radius is associated with these interactions. In previous simulations, the reaction radius was taken to be a constant value estimated using a simple approximation based on infinite, parallel dislocation lines. Here, a continuum-based elasticity approach is taken to more accurately quantify the reaction radius by comparing the Peach-Koehler force of one dislocation acting on another at a free surface with the lattice resistance to dislocation motion. The presence of the free surface gives rise to a moderate reduction of the interaction force. Results are compared with preliminary experimental data for GaAs films grown on InP.

We present real time observations of the interaction of dislocations in heteroepitaxial strained layers using a specially modified ultrahigh vacuum transmission electron microscope equipped with in-situ deposition capabilities. These observations have led to delineation of the regime of epilayer thickness and composition where dislocation interactions result in blocking of the propagating threading segment. It is found that both the blocking probability as well as the magnitude of the dislocation interaction force are strongly dependent on the Burgers vectors of the dislocations involved, with the greatest effects observed when the Burgers vectors of the two dislocations are parallel with respect to each other. Frame-by-frame analysis of the motion of the dislocation threading segment during interaction is used to extract the magnitude of the interaction stresses as a function of both the level of heteroepitaxial strain and the dislocation geometry. Finally, by continuing growth following observations of blocking during annealing, we find that blocked dislocations are likely to remain in that configuration until substantial additional heteroepitaxial stresses are incorporated into the layer. These results have direct relevance to the successful integration of strained layer heterostructures into electronic device applications. This is because blocked threading segments result in the introduction of undesired band gap states, enhance impurity diffusion, modify surface morphology and act to limit the dislocation density reductions achievable in graded buffer structures.

We demonstrate a new approach to the growth of dislocation free lattice-mismatched materials on GaAs substrates using Al2O3 interlayers obtained by lateral oxidation of AlAs. This is achieved by generating relaxed low threading dislocation density InGaAs templates which are mechanically supported but epitaxially decoupled from the host GaAs substrate. This process uses the phenomena of relaxation of strained coherent hypercritical thickness (h > hcritical,) layer in direct contact with an oxidizing Al-containing semiconductor (i.e. AlAs or AlGaAs). 5000 Å In0.11Ga0.89As layers were then grown on the In0.2 Ga0.8As/Al2O3/GaAs template which acts as a pseudo-substrate (lattice-engineered substrate). The epitaxial layers are partially relaxed and have extremely smooth surface morphology. Further TEM micrographs of these epitaxial layers show no misfit dislocations or related localized strain fields at the In0.2Ga0.8As/Al2O3 interface. The absence of misfit dislocations or local strain contrast at the In0.2Ga0.8As/Al2O3 interface is attributed to both reactive material removal during the oxidation process and the porous nature of the oxide itself. We propose that the strain relaxation in In0.3Ga0.7As is enhanced due to the absence of misfit dislocations at the In0.2Ga0.8As/A12O3 interface.

To engineer high-quality InxGal-xP graded buffers on GaP substrates (InxGa1-xP/GaP), we have explored the evolution of microstructure and dislocation dynamics in these materials. We show that the primarily limiting factor in obtaining high-quality InxGa1-xP/GaP is a new defect microstructure that we call branch defects. Branch defects pin dislocations and result in dislocation pileups that cause an escalation in threading dislocation density with continued grading. The morphology of branch defects is dominated by growth temperature, which can be used to suppress the strength or density of branch defects. In the absence of branch defects, we observe nearly ideal dislocation dynamics that are controlled by the kinetics of dislocation glide. This new understanding results in two primary design rules for achieving high-quality materials: 1) control branch defects, and 2) maximize dislocation glide kinetics. Combining these design rules into optimization strategies, we develop and demonstrate processes based on single and multiple growth temperatures. With optimization, threading dislocation densities below 5 × 106 cm−2 are achieved out to x = 0.39 and a nearly steady-state relaxation process is recovered.

The selective growth of GaAs by HVPE was studied on (001), (110), (111)Ga and (111)As, GaAs patterned substrates by varying the I1I/V ratio. A kinetic modelling of the growth was developed, based upon the SEM observations of the growth morphologies as well as on experimental curve synthesis. The growth rate is written as a function of the diffusion fluxes of the adsorbed AsGa and AsGaCI molecules and takes into account the chlorine desorption by H2. 1.5 μm thick GaAs films were then fabricated on Si (001) by a confined epitaxial lateral overgrowth technique. These conformal films exhibit intense and uniform luminescence signals, showing that the dislocation densities of GaAs are lower than 105 cm−2. SEM analyses reveal that conformal growth fronts consist in (110) and (111)As A planes under the III/V ratios (superior to 1) which were tested.

The growth of reduced dislocation density GaAs/Si is performed by a novel two-step technique where the first epitaxy step takes place at 75° C and the second is performed at 580° C. The initial deposition is single crystal, continuous, and planar such that there is no contribution to the dislocation density from Volmer-Weber island coalescence and no trapping of dislocations in pinholes. Using this new growth technique, a reduced dislocation density the order of 106/cm2 was obtained. The improved crystallinity is indicated by the more narrow x-ray full-width-at-half-maximum (FWHM) value of 110 arcseconds. GaAs p-i-n diodes were grown on the reduced dislocation density GaAs/Si and it was found that the resistivity of the intrinsic region for the heteroepitaxial diodes was similar to homoepitaxial ones for small mesa sizes.

We realized “compliant” substrates in the square centimeter range by twist-wafer bonding of an (100) GaAs handle wafer to another (100) GaAs wafer with a several nm thick epitaxially grown GaAs layer followed by an appropriate back-etch procedure. The twist angle between the two GaAs wafers was chosen between 4 and 15 degrees. The twisted layers were characterized by area scanned X-ray diffraction, optical and electron microscopy and atomic force microscopy. Occasionally we observed regions showing pinholes in the transferred thin twistbonded GaAs layer.

After epitaxial deposition of 300 nm InP and InGaAs films with different degrees of mismatch on these substrates, transmission electron microscopy revealed grains which are epitaxially oriented to either the substrate or the twist-bonded layer. The grain boundaries between the twisted and untwisted grains probably collect threading dislocations, thus reducing their density in the areas free of boundaries.

An epitaxial GaAs layer was grown on a CaF2 (111) by means of surface free energy modulation of CaF2 by one-monolayer-height island formation. An additional low-temperature growth at a final stage of growth of the CaF2 layer on Si(111) produced high density islands whose height was one monolayer of CaF2. This surface structure contributed to enhance wettability of overgrown GaAs. Two-step growth sequence was also examined in order to grow GaAs layer on the modified CaF2/Si(111) with good crystallinity. The electron mobility of 2,000cm2/Vs in a Si doped GaAs layer (6×1017 cm−3) was obtained by the combination of the surface energy modulation method and the two-step growth method.

Deep level defects in MOCVD-grown, unintentionally doped p-type InGaAsN films lattice matched to GaAs were investigated using deep level transient spectroscopy (DLTS) measurements. As-grown p-InGaAsN showed broad DLTS spectra suggesting that there exists a broad distribution of defect states within the band-gap. Moreover, the trap densities exceeded 1015 cm−3. Cross sectional transmission electron microscopy (TEM) measurements showed no evidence for threading dislocations within the TEM resolution limit of 107 cm−2. A set of samples was annealed after growth for 1800 seconds at 650 °C to investigate the thermal stability of the traps. The DLTS spectra of the annealed samples simplified considerably, revealing three distinct hole trap levels with energy levels of 0.10 eV, 0.23 eV, and 0.48 eV above the valence band edge with trap concentrations of 3.5 × 1014 cm−3, 3.8 × 1014 cm−3, and 8.2 × 1014 cm−3, respectively. Comparison of as-grown and annealed DLTS spectra showed that post-growth annealing effectively reduced the total trap concentration by an order of magnitude across the bandgap. However, the concentration of a trap with an energy level of 0.48 eV was not affected by annealing indicating a higher thermal stability for this trap as compared with the overall distribution of shallow and deep traps.

We have investigated the direct growth of narrow-gap InAs on wide-gap GaP by Molecular Beam Epitaxy. InAs and GaP have the largest mismatch among all the III-arsenides and the III-phosphides – 11%. A perfect epitaxial relationship is maintained between the InAs and the GaP despite the large lattice mismatch. Moreover, a reproducible defect structure with unique electronic properties is developed at the heterointerface. A point defect associated with the intersection of 90° misfit dislocations may act as an ordered, structural dopant. This dopant is fully ionized with a constant, high sheet carrier density of 1013 cm−2, independent of InAs layer thickness, and exhibits no freeze out even at 5 K. Device applications for such a system include temperature insensitive Hall sensors. We have also demonstrated high electron mobilities (over 10000 cm2/V-sec) in nominally undoped thick InAs layers grown on GaP. The explanation of this effect is presented to emphasize the exciting possibilities of band gap engineering in this system.

ZnSe-GaAs(001) heterovalent quantum structures, multiple quantum wells (MQWs), were fabricated. Since the band offsets in this heterovalent heterostructure are controllable, different offsets can artificially be put at both sides of the GaAs wells, which may lead to modification of the electronic properties of the MQWs. This hypothesis was examined by the optical absorption measurement. Consequently, by changing the valence band offset at the GaAs-on-ZnSe interface from 0.6 to 1.1 eV, while keeping that at ZnSe-on- GaAs constant at 0.6 eV, the absorption edge energies of the MQWs shifted from 1.43 to 1.37 eV. This indicates the presence of an internal electric field and the capability of controlling the electronic properties of heterovalent MQWs with the completely same structural parameters. The numerical analyses of the Poisson and Schrddinger equations well explain the trend of this experimental result.

Deep level defects have been detected and analyzed in epitaxial ZnSe layers grown by molecular beam epitaxy (MBE) on GaAs and on In0.04Ga0.96As using deep level optical spectroscopy (DLOS). A series of samples, which differ only in the initial Zn:Se beam pressure ratio (BPR = 1:1, 1:10, 10:1) during the growth nucleation step, were characterized by DLOS in order to assess the dependence of bulk deep level formation on interface nucleation conditions. The transient and steady state photocapacitance measurements were performed using 100 W Quartz Halogen and 450 W Xe lamps as light sources, in the spectral range of 0.9 to 2.9 eV with a resolution better than 0.02 eV. The capacitance transients were recorded for time windows of 10 msec to 5 sec after light excitation of the sample, which was kept at a temperature of 100 K. Using semi-transparent Au Schottky contacts, several deep levels in the ZnSe layer were detected for all BPR's, with optical threshold energies of 1.1, 1.46 and 1.9 eV below the conduction band. These energies were obtained from the slope of the capacitance transient at different time intervals and were confirmed by steady state photocapacitance. The concentration of the levels was in the range 1012 to 1014 cm−3. Both the 1.1 and 1.46 eV trap concentrations were found to depend strongly on lattice mismatch conditions, whereas the latter was shown to largely depend on BPR. The optical threshold of the 1.9 eV trap correlates well with a ˜1.9 eV cathodoluminescence (CL) peak, which has been previously associated with either Zn vacancies or Gazn substitutional defects in Zn-deficient material.

Zincblende ZnxCdl−xSe alloys were grown on (001) InP by organometallic vapor phase epitaxy (OMVPE) using various VI / H precursor flow ratios, ranging from 0.95 to 12, at a temperature of 420°C. Spatial distribution of luminescent centers in the epilayer was characterized by cathodoluminescence (CL) spectroscopy and imaging. Both near band-gap (NBE) and deep level (DLE) emissions were observed in the spectra, with the width of the NBE peak increases with the VI / II flow ratio. Monochromatic CL images showed that the broadening of the NBE peak has its origin in the spatial inhomogeneity of the luminescent centers of the epilayer. Extended defects responsible for the DLE was only found in pyramidal hillocks seen in the CL images. The density of these defects was found to increase with the VI / I1 flow ratio.

Discrete and coalesced monocrystalline layers of lateral- and pendeo-epitaxially grown GaN and AlxGal−xN layers originating from GaN stripes deposited within windows contained in SiO2 masks or from side walls of GaN seed structures containing SiNx top masks have been grown via organometallic vapor phase deposition on GaN/AlN/6H-SiC(0001) substrates. Multilayer heterostructures of GaN and AlxGal−N were also achieved. Scanning and transmission electron microscopies and atomic force microscopy were used to evaluate the microstructures, the type and distribution of dislocations and the surface roughness of the resulting films. The extent and microstructural characteristics of the laterally overgrown GaN regions were a strong function of stripe orientation and temperature. These regions contained a low density of dislocations. The RMS roughness of the (1120) sidewall plane of the pendeoepitaxial structures was approximately 0.100 nm.

We have demonstrated the ability to bond thin layers of Si {111} onto either silicon dioxide or silicon nitride coated Si {100}. This was achieved using a “Smart-Cut” process. The integration of SiN required chemical mechanical polishing. The growth of GaN on a thin Si {111} on oxide on Si {100} stack was demonstrated.

In this paper we discuss the growth and characterization of 3C-SiC epitaxial layers grown on both a Si substrate as well as on a novel substrate. The growth uses a typical three step process. First an etch of the Si surface is performed, second the surface of the Si is carbonized and third 3C-SiC is grown on the carbonized surface. Several characterization techniques were used to verify the quality of the 3C-SiC film. Microscopy was used to investigate the surface morphology, X-ray and electron diffraction were used to determine crystal structure, cross section TEM was used to verify crystal structure and highlight twinning, and x-ray topography was used to measure the strain fields induced in Si substrate at the 3C-SiC/Si interface.

Epitaxial wurtzite aluminum nitride (AIN) films have been grown on (111) oriented silicon substrates by plasma-assisted solid source molecular beam epitaxy (MBE). The growth has been performed in the two-dimensional (2D) growth mode. Occuring surface reconstructions have been monitored by reflection of high-energy electron diffraction (RHEED). The films have been characterized by atomic force microscopy (AFM) and transmission electron microscopy (TEM). 2D grown films exhibit atomically smooth surfaces, are singlecrystalline and void of oriented domains. High-resolution (HR) TEM micrographs of the heterointerface show the presence of an interfacial atomic arrangement where (5:4) unit cells coincide along the AIN[2110]/Si[110] direction.

Surface acoustic wave (SAW) properties of MBE-grown AIN(0001)/Si(ll1) have been studied for the first time. The AIN film exhibits very good piezoelectricity. The SAW time response indicates low scattering of the waves during their propagation. An electromechanical coupling coefficient (EMC) of 0.07% has been measured for the present interdigital transducer (IDT) geometry.

A new approach for one-dimensional photonic bandgap formation is introduced. The method consists of wafer bonding and delamination, which is capable of stacking single crystalline semiconductor layers on non-crystalline insulator layers. Si and SiO2 layers with sub-wavelength periodicity are successfully stacked to form photonic crystals consisting of 3 pairs without a defect layer and of 4.5 pairs with a defect layer. The transmittance spectra are well reproduced by transfer matrix calculations. This clearly verifies the potential of the wafer bonding and delamination method.

Two clean and flat wafers can adhere spontaneously. The technique has recently led to novel electronic and optoelectronic devices. The adhesion arises from short-range interatomic forces between wafer surfaces, which can be represented by a reduction in surface energy associated with the transformation of two surfaces into one interface. The wafers, however, are seldom perfectly flat; the misfit has to be accommodated by elastic distortion, plastic deformation, or mass transport. We model elastic accommodation in this paper. The distortion causes the wafers to gain elastic energy. If the surface energy reduction dominates over the elastic energy gain, the wafers will bond. We solve the three dimensional elastic field in the misfit wafers analytically. The conditions for bonding are established, and practical implications discussed.