A critical layer thickness study of strained GaAs/InGaAs and AlGaAs/GaAsP quantum wells (QWs) grown by atmospheric pressure organometallic chemical vapor deposition (OMCVD) is reported. Characterization by conventional photoluminescence (PL), photoluminescence excitation (PLE) spectroscopy, optical microscopy, and x-ray diffraction suggests that partial or regional relaxation begins to occur at critical thicknesses predicted by the force-balance model. To test the stability of strained quantum wells with well width near or exceeding the predicted critical thickness, annealing up to 850°C for ten minutes was carried out. No sign of degradation or complete relaxation of the QW layers was observed.

We have demonstrated that shallow ion (75As+) implantation and rapid thermal annealing (RTA) of strained InGaAs/GaAs quantum well (QW) structures can modify the optical properties of these epitaxial semiconductor heterostructures in a spatially selective manner. After RTA, exciton QW energies, determined from peaks in the photoluminescence spectra, shifted significantly to higher values only in the implanted regions. The magnitudes of the shifts were dependent on QW widths, RTA temperatures, and implantation fluences. The shifts were interpreted as resulting from the modification of the shapes of the as-grown QWs from square (abrupt interfaces) to rounded (gradual interfaces) due to enhanced indium diffusion out of the well layers in irradiated areas as a consequence of the diffusion of vacancies generated near the surface by the implantation. The thermal processing had only a small effect on the strain present in the quantum well layers due to the difference in the lattice constant of the well and barrier layers.

In this work we have studied the effects of silicon planar doping on the electrical and optical properties of GaAs, and the effects of rapid thermal annealing on AIGaAs planar-doped structures. MBE-grown GaAs epilayers with multiple planar-doped layers displayed a 1.2 eV photoluminescence peak, presumably due to gallium vacancy - donor complexes, for samples with nominal silicon sheet densities much greater than measured charge densities. The Hall mobilities of these samples were also reduced compared to both uniformly-doped and planar-doped structures whose silicon areal densities were more nearly equal to measured sheet charge densities, although X-Ray rocking curves were nearly identical in all cases. Planar-doped AIGaAs Schottky diodes had nearly ideal electrical characteristics. Rapid thermal annealing of the planar-doped structures before fabrication increased the diode ideality factor from n=1.06 to n=1.60, seriously degraded the saturation current and breakdown voltage, and increased the doping profile FWHM from 60Å to 170Å.

Inx Ga1-x As thin films were grown by MBE on (001) GaAs substrates. The associated 1% lattice mismatch resulted in the development of an elastic strain field in the systems. Electron channeling patterns (ECP) were then obtained from these samples in an SEM at different accelerating voltages, allowing data to be obtained over various information depths within the samples while keeping them intact. The ECPs showed sensitivity to the elastic strains both parallel and perpendicular to the film/substrate interface. Certain high order Laue zone (HOLZ) line positions showed good sensitivity to the Poisson strain in the films due to a rotation of atomic planes. These line positions varied with film thickness and distance from the interface. The technique shows promise as a tool for relatively easy elastic strain determination. Its limitations will also be discussed.

Interdif fusion of Al and Ga in a Si modulation doped AlAs/GaAs superlattice was studied by photoluminescence technique. The diffusion coefficient of Al and Ga in the modulation doped superlattice is 1/3 to 1/2 of that of uniformly doped superlattice with the same average Si concentration. The dependence of the diffusion coefficient on the average Si concentration is similar to that of uniform doping.

Single layers of ~ 0.5µm thick InuGa1-uAs1-vPv (0.52 < u < 0.63 and 0.03 < v < 0.16) were grown epitaxially on InP(100) substrates by liquid phase epitaxy at ~ 630°C. The compositions of the films were chosen to yield a constant banndgap of ~ 0.8 eV (λ = 1.55 µm) at room temperature. The lattice mismatch at room temperature between the epitaxial film and the substrate varies from - 4 × 10-3 to + 4 × 10-3. The strain in the films was characterized in air by x-ray double crystal diffractometry with a controllable heating stage from 23°C to ~ 700°C. All the samples have an almost coherent interfaces from 23°C to about ~ 330°C with the lattice mismatch accomodated mainly by the tetragonal distortion of the epitaxial films. In this temperature range, the x-ray strain in the growth direction increases linearly with temperature at a rate of (2.0 ± 0.4) × 10-6/°C and the strain state of the films is reversible. Once the samples are heated above ~ 300°C, a significant irreversible deterioration of the epitaxial films sets in.

The Rayleigh acoustic waves of sputter-deposited Cu/Co, Ag/Pd and Cu/Pd sup-erlattice films were studied using Brillouin scattering. All three of these systems are fcc/fcc superlattices. The dependence of the Rayleigh wave velocities for these films on the superlattice modulation wavelength is discussed.

Bilayers of Cu/Fe and Cu/V and multilayers of Ni/Fe have been grown under high vacuum and ultra high vacuum conditions respectively with [111] epitaxy. Multilayer layer thicknesses ranged from 3 monolayers to 15 monolayers per layer. Improved epitaxy of the UHV growth was, we believe, due to the better vacuum although perfect material could only be obtained for growth within a narrow and shifting substrate temperature ‘window’. Possible shortfall in the quality of the Cu backing layer epitaxy was averted by a 2hr anneal at 425°C.

In the Fe/Ni multilayers the Fe was observed to adopt the FCC lattice rather than the equilibrium BCC lattice for layer thicknesses less than 10 monolayers. This change of structure coincided with a reduction in sample magnetic moment per volume attributed to a collapse of the Fe moment to a value 7 times less than bulk.

The Ni/Ag interphase boundary structure in the parallel cube-on-cube orientation was studied for the boundary planes (001) and (011). Coarsely spaced dislocations were found in all annealed interfaces; the origin of these was apparently differential thermal expansion of the bicrystal film. A detailed search for intrinsic periodic structure consistent with the O-lattice construction was made using X-ray diffraction, electron diffraction and transmission electron microscopy . No evidence for this could be found; such a relaxation, if present, is very weak. It is unlikely that such a small relaxation could account for the relative energy minimum associated with the parallel cube-on-cube orientation found by previous investigators.

The strain distribution within individual layers in Au/Ni multilayer systems was obtained by an iterative fitting of the experimental x-ray diffraction pattern with a kinematic model. The depth profile of strain in the modulation direction was obtained for these metallic multilayers with repeat periodicities ranging from 1.19 nm to 4.26 nm. It was found that the role of interfacial coherency and strengthening is of great importance in understanding the origin of the supermodulus effect in metallic multilayers.

Epitaxial growth of thin films, alloys, and multilayers from the Cu-Ni system are being explored as a means of fabricating a substrate to lattice match diamond. These single crystal films are superior to commercially available substrate material. Due to the high reactivity of the metal surfaces in atmosphere, all processing must be done under UHV conditions. In vacuo preparation, growth, and analysis of the metals is described.

We have studied the epitaxial growth and structural properities of single crystal Fe/Ag and Mn/Ag superlattices grown on (001) GaAs substrates using transmission electron microscopy. A buffer layer of Ag (001) was grown on a 5 monolayer Fe seed layer on the (001) GaAs substrate before the growth of the superlattice to obtain good quality films. For some samples an intermediate buffer layer of ZnSe was used, as well. Both Fe/Ag and Mn/Ag superlattices with a Ag buffer layer show very sharp interfaces. The densities of dislocations in the film and the buffer layer are the same suggesting that the dislocations originate at the film/substrate interface. We have observed evidence for a strain modulation of ≈ 8 Å in the Mn layer for thick (≈ 22 Å) Mn layers in the superlattice samples but not in samples with a thin Mn layer.

The growth of Mo overtayers and Mo-Ni multilayers on single crystal Ni(001) substrates is described. The nucleation and growth processes of these thin films were analyzed by LEED, XPS, AES and SEM and High Resolution AES investigations without breaking vacuum. Growth of Mo-Ni multilayer heterostructures on Ni(001) with ≈20Å periodicity is possible at low temperature (≈200 °C). At high temperature (≈550 °C) the growth proceeds by the Volmer-Weber mechanism preventing the deposition of small period multilayers. Annealing experiments on ultra-thin (<20Å) Mo overiayers deposited at 200 °C show an onset of interdiffusion at ≈ 550°C coupled to the generation of a new surface periodicity.

The epitaxial growth kinetics of Co on Cu(100) are investigated with a kinetic solid-on-solid model. Two effects are found to dominate the growth of this system reflecting the difference in surface free energies betweenthe two materials: the difference of diffusion parameters, and the inability of Co to wet Cu(100) at lower temperatures.

Epitaxial films of Ag(111) were grown by Molecular Beam Epitaxy (MBE) on small angle misoriented Si(111) substrates. The surface normal was tilted 0 to 6° away from the Si(111) axis toward the [112] direction. The structure of the films was analyzed by x-ray diffraction and MeV He+ ion channeling. Despite a large lattice mismatch, good quality epitaxial films, 600–1200 Å thick, were grown on the misoriented Si substrates. Interestingly, the angle between the Si(111) axis of the substrate and the Ag(111) axis of the film (the misalignment angle) is not zero. In contrast to the perfect alignment on a flat substrate, the Ag(111) axis is tilted away from the Si(111) axis toward the surface normal. Axial MeV He+ ion channeling shows the misalignment angle (up to .6°) increases with substrate misorientation angle (~1/10 substrate misorientation angle).

We report X-ray diffraction and in-situ RHEED( Reflection High Energy Electron Diffraction) measurements on Cr thin films deposited on LiF[001] single crystal substrates for thicknesses up to 300 nm and for substrate temperatures from 30 to 450°C. From these measurements we determine the range of deposition conditions necessary for epitaxial growth and the stress in these films as a function of film thickness.

The structural and electrical properties of epitaxial CoSi2, grown on Si(001) by molecular beam epitaxy, have been investigated. Most growth conditions successful on Si(111) have been found to result in misoriented grains when applied to Si(001). However, single-orientation (001) CoSi2 films, with low resistivities (16 µΩ-cm) and low ion channeling minimum yields (χmin=5%), have been obtained by direct codeposition of Co and Si at ~500°C at Co-rich stoichiometries. Single orientation (001) CoSi2 films have also been obtained by using a template method on epitaxially grown Si buffer layers, but the resistivities of these films have not been as good. A Schottky barrier height of 0.71 eV has been measured for single-orientation CoSi2(001)/Si(001). This is significantly higher than the barrier height of 0.64 eV for CoSi2(111)/Si(111).

Growth of high quality type-B oriented NiSi2 and CoSi2 on Si(111) at room temperature was demonstrated recently. It is proposed that a few monolayers of metal reacts with Si(111) to form type B disilicide which then serves as a template for subsequent homoepitaxial growth during co-deposition. Thin, pre-annealed, silicide layers on Si (100) and (110) arc used as templates to demonstrate the homoepitaxial growth of NiSi2 and CoSi2 along these two directions at room temperature. The high temperatures usually required for the formation of NiSi2 and CoSi2 are related to the nucleation and mass transport processes.

Thin film stresses accompanying the nucleation and growth of NiSi2, resulting from the interaction of polycrystalline nickel films with (001) and (111) silicon substrates, have been measured at an annealing temperature of 825° C. Results Indicate a significantly larger stress reduction during the formation of NiSi2 on (111) silicon ( ~ 200 MPa) whereas the stress reduction is comparatively small (50–100 MPa) for the formation of NiSi2 on (001) silicon. TEM studies reveal that for NiSi2 on (111) silicon, two sets of dislocations in edge or mixed orientation are initially produced - one set consisting of Shockleys spaced 25Onm and a second set consisting of 5Onm spaced Shockleys; dislocations and their Burgers vector lie in the growth interface. For NiSi2 on (001) silicon, dislocations are rarely observed, however, a large concentration of ledges or facets are observed in an orthogonal network lying at the NiSi2 - (001)Si interface.

It is argued thai the observed stress reduction of NiSi2 on (111)Si is due to concurrent dislocation multiplication and interfacial glide of the Shockley partials. Larger compressive stresses of NiSi2 on (111) silicon at the annealing temperature is attributed to the accumulation of the edge type Shockleys present in the NiSi2 phase. In contrast, the negligible decrease in stress during the formation of NiSi2 on (001) silicon is believed to result from the presence of sessile misfit compensating ledges which lie at the NiSi2-Si interface.

Epitaxial columns of CoSi2 are produced when Si and Co are codeposited on heated Si substrates. These columns are surrounded by epitaxial Si with defect densities below the detection limit of transmission electron microscopy. This phenomenon has been studied as functions of substrate temperature, Si:Co ratio, deposition rate, thickness of the epitaxial layer, and substrate orientation. These data suggest that the distribution of columns is dictated by the nucleation of CoSi2 islands during the initial stages of the deposition.