The molecular beam epitaxy growth of GaAs homoepitaxial films has been studied. Scanning tunneling microscopy images show that in the earliest stages of growth the surface morphology oscillates between one with two-dimensional islands and flat terraces. Concomitant with the decay of the RHEED oscillations, the surface morphology evolves to a dynamical steady state characterized by a constant value of the step density. Numerical models of the growth allow a prediction to be made for the asymtotic value of the step density. On a larger length scale (approximately 10 micrometers ) the surface morphology is found to consist of large mounds. The angle of the mounds with respect to the substrate is fixed and is determined by the separation between nucleating islands. This growth instability is found for singular surfaces and is absent for vicinal surfaces grown under step flow conditions.

RHEED oscillations were studied for GaAs growth for azimuthal angles of 0 degree(s) and 15 degree(s) as the angle of incidence was changed between 0.4 degree(s) and 1.7 degree(s). The angle of incidence was then held constant while the azimuthal angle was varied from 0 degree(s) to 85 degree(s). From the recorded oscillations the static surface intensity, oscillation intensity, oscillation phase, and dampening were extracted. The static surface intensity was found to change with angle and displayed a trend very similar to that reported in the literature. The intensity of the oscillations was found to vary periodically with angle of incidence and thus supported the theory that interference between layers of different height is one source of the oscillations. However, the phase of the oscillations deviated from that predicted by a simple, kinematic-scattering interference model. The dampening of the oscillations was found to vary strongly with angle of incidence. There existed a range of angles of incidence over which the phase was close to that expected for a simple interference model and for which the dampening was essentially constant.

It is well known that PH₃ is highly toxic and safer alternatives need to be found. TBP has a favorable vapor pressure at room temperature and decomposes at a lower temperature than PH₃. Results of a systematic investigation of the pyrolysis of novel phosphorous (P) precursors for chemical beam epitaxy (CBE) that are safer than phosphine are presented. In particular, three topics pertinent to CBE are presented: (1) technical details on the pyrolysis conditions and growth using several novel condensed-phase P-precursors, including tertiarybutylphosphine (TBP); (2) a custom-designed gas-source group V cracker cell; and (3) methods to reduce the cracking temperature of P-containing sources.

Control of the morphology of epitaxial thin films is a prerequisite for device applications. Particularly crucial is the formation of smooth and defect-free hetero-interfaces at elevated temperatures where cluster formation is thermodynamically favored. In particular knowledge of the early stage of clustering is crucial as nucleation often results in aggregates of a few atoms which could still be integrated during further growth. Only few data exist for this stage to date due to small cluster sizes and the transient time behavior which complicate measurements with most standard surface techniques. An alternative approach is described to study the early stage of cluster growth as a by-product in late stage growth experiments. When applicable, like in the case of Ga clustering on GaAs(001) as discussed in this paper, simpler technical access and higher precision in the determination of a time scale favor this method.

Stress-modulated surface kinetics offers a possible path to the ultimate fracture of brittle solids. Similarly, it leads to a breakup of growing strained layer into the separate domains- islands. A proposed reduced description of a single growing concavity and an interpolation between small and large amplitude limits lead to a two-parameter model of the islanding precursor: it starts from a smooth boundary and generates a sharp cusp, which enables a further growth of incoherent islands. Within the `local description' approximation we outline a general dynamic behavior of stressed interface, with the possibility of relaxation loops; they may be responsible for the barrierless formation of dislocations and stress relief.

The localized growth of III-V epitaxial structures on substrates patterned with dielectric masks provides a flexible technique for the monolithic integration of electronic and optoelectronic devices. Chemical beam epitaxy (CBE) is an attractive growth technique for use in this approach and interest has consequently focussed on the reaction mechanisms which give rise to selective area growth in CBE. In the present paper we therefore seek to describe the molecular surface chemistry involved. In contrast it is shown that the sticking probability of Gp III precursors on the dielectric masks employed in selected area epitaxy is vanishingly low, and any free Gp III species produced become trapped in an inert oxidized form within the surface layers. As a result the production of metallic Gp III species on the surface does not occur, hence growth of the III-V semiconductor is not observed. Adsorption of the Gp V species on the dielectric mask is shown to promote decomposition of the Gp III precursors, resulting in a loss of selective growth at high V-III incident flux ratios or low growth temperatures.

Spontaneous CuPt-type ordering of Group III atoms on the (111) subplanes of the GaInAs₂ and AlInAs₂ epitaxially deposited by atmospheric pressure organometallic vapor phase epitaxy is observed by transmission electron microscopy. We find positive correlation between the observation of CuPt-like (111) superlattice diffraction spots in transmission electron diffraction (TED) patterns and reduced band gap energies, with a reduction of more than 75 meV for GaInAs₂ and 25 meV for AlInAs₂. For these materials, ordering depends strongly on growth temperature, but only moderately on substrate misorientation. Room temperature time-resolved photoconductivity of ordered GaInAs₂ exhibit 50 microsecond(s) ec decay and behavior indicative of carrier localization.

A detailed study of growth characteristics of highly strained extremely thin InAs and GaAs layers on InP substrates was made. Single strained layer heterostructures as well as short- period strained-layer superlattices (SPSLSs) were grown with low-pressure metalorganic vapor phase epitaxy. Different growth parameters were varied to clarify the influence of growth temperature and growth time on growth rate or layer quality of extremely thin InAs and GaAs strained layers. InAs/In_0.53Ga_0.47As, GaAs/In_0.53Ga_0.47As and InAs/GaAs/In_0.53Ga_0.47As superlattice test structures were developed and realized providing information about growth rates and layer quality of InAs an GaAs under strain in SPSLSs. All test structure types were grown with respect to the special requirements of high resolution x ray diffraction (HRXRD). Samples with various strained layer thicknesses were analyzed by HRXRD and compared with simulation results. Simulations based on the solution of the Takagi-Taupin equations of the dynamical diffraction theory were made using a commercial simulation program.

We use the ex-situ technique of magneto-optical spectroscopy to characterize MBE-grown Co, Co-Pt, and evaporated Co-Ni films and show that subtle changes in the structural and chemical order as well as changes in the crystallographic properties can substantially affect the magneto-optical spectra. These can be viewed as a sensitive probe of the spin-polarized electronic structure of a magnetic material, which in turn is strongly structure dependent. In particular, we discuss the effect of the crystallographic phase on the spectra of 1000 angstrom thick fcc and hcp Co and fcc and hcp Co₈₂Ni₁₈ films in the photon energy range 08 - 5.5 eV. In Co_1-xPt_x alloys, of compositions x approximately equals 0.75 and approximately equals 0.5, large changes in the magneto-optical spectra are observed if chemical ordering is induced either by annealing below the disorder-order transition temperature or by direct growth near the ordering temperature. Other examples are the discovery of a new chemically ordered, hexagonal Co-Pt phase at the composition x approximately equals 0.25 and an unprecedented large Kerr effect in the chemically ordered Fe₁Pt₁ (L1₀) phase.

The growth and annealing properties of Pd overlayers on Cu(100) have been investigated using re-emitted positron spectroscopy, low energy electron diffraction, and Rutherford backscattering spectroscopy. Two changes in the growth mode of the Pd overlayers have been observed at approximately 0.5 and approximately 1 monolayer Pd coverage. These changes correspond to the completion of the first and second alloy layers, the latter also being associated with the beginning of the growth of bulk Pd. The bulk Pd film does not grow in an epitaxial manner and was found to contain approximately 1% vacancy defects. For 0.5 monolayer Pd/Cu(100) overlayers annealing at 353 K has been observed to result in the loss of Pd from the surface to the bulk and the removal of defects associated with the overlayer.

MBE is a powerful synthesis technique for preparation of ordered intermetallic phases since the high rates of surface diffusion allow in-plane chemical ordering to occur at temperatures far below those which are necessary for ordering in bulk samples. This lifting of kinetic constraints enables the phase diagrams to be explored at low temperatures where bulk ordering processes are often too sluggish for phase equilibria to be reached. Specifically, we describe the preparation of epitaxial films (in the thickness range 100 - 1000 angstrom) of ordered intermetallic phases in the Co-Pt and Fe-Pt intermetallic systems. Such phases are of potential importance for magnetic and magneto-optical storage applications. In particular we discuss growth and chemical ordering in epitaxial Co_1-xPt_x films near x equals 0.25, 0.5, and 0.75 as well as Fe_1-xPt_x films near x equals 0.5. Depending on growth conditions these phases order spontaneously during growth with resulting changes in the Kerr spectra. Ordering results in large Kerr rotations (approximately 1 degree(s)) in the UV spectral region for the films with x near 0.5.

The deposition of Fe on Al(100) at 295 and 200 K has been investigated with Rutherford backscattering (RBS), low energy electron diffraction, Auger spectroscopy, angle resolved Auger electron spectroscopy, surface magneto-optic Kerr effect (SMOKE) and Brillouin light scattering measurements. The initial deposition of Fe results in the Fe alloying with the Al substrate, producing a disruption in the near-surface order. By a Fe coverage of 1 ML both the short-range and long-range order is completely disrupted. As deposition continues the alloying is observed to end, and for coverages > 5 ML a poorly ordered bcc Fe(100) overlayer, rotated 45 degree(s) from the Al(100) substrate, is observed. Annealing this poorly ordered overlayer results in the Fe alloying into the substrate. The magnetic properties of the Fe/Al(100) overlayers also are discussed.

Modern thin film growth techniques have enabled the realization of low dimensional semiconductor heterostructures and hybrid metal/semiconductor structures with properties tailored for a variety of device applications. It has been empirically established, for example, that the net magnetic anisotropy exhibited by a simple metal epitaxial film on a semiconductor is strongly affected by the interactions at the metal/semiconductor interface, although the mechanisms have not been systematically addressed and remain an open issue. An understanding of these mechanisms is prerequisite to obtaining a fundamental description of anisotropy, and has significant implications for successful realization of spin sensitive device structures. We consider here how contributions to the net magnetic anisotropy arise from the formation of the interface and early stages of metal film growth. We suggest that these contributions originate in the initial metal adsorption sites and subsequent bond or site filling, and are strongly dependent on the semiconductor surface reconstruction. We consider specifically the cases of the epitaxial growth of Fe films on the various reconstructions of the ZnSe(001) and GaAs(001) surfaces, and attempt to interpret the net magnetic properties in light of the atomic structure of the film and interface.

We report the molecular beam epitaxial growth of the quaternary (Zn,Mg)(S,Se) compound as well as the incorporation of this quaternary into a pseudomorphic SCH blue-green laser diode configuration. X ray diffraction and TEM imaging indicate that the quaternary (Zn,Mg)(S,Se) can accommodate substantially more strain than the binary ZnSe; pseudomorphic epilayers with thickness of about 2 micrometers could be grown within a strain range of -0.225% (tension) and 0.137% (compression) at room temperature. Room temperature continuous wave operation of diode lasers having the quaternary as cladding layers was achieved with a lifetime of longer than 20 seconds. These index-guided laser diodes, employing the Zn(Se,Te) graded ohmic contact (adopted to contact p-type (Zn,Mg)(S,Se), have provided a significant reduction in lasing threshold voltage to 4.2 V.

ZnSe_1-xTe_x layers were grown by MOVPE on (111) and (001) GaAs substrates at 340 degree(s)C. The growth process of the ternary compound is described by a thermodynamical analysis. The structural quality of the films was determined by x-ray diffraction and transmission electron microscopy. In the present work it is shown that in the case of (001) GaAs substrates the density of misfit dislocation lines extending into the epilayer is reduced drastically by improved oxide removal. For ZnTe/GaAs (111) misfit dislocations can spatially be confined to a narrow (approximately 10 nm) region close to the interface.

The strained InAsP/InP system can be a viable alternative material to the quaternary InGaAsP on InP because the composition and thickness of InAsP can be controlled independently in gas- source MBE and because strain could provide another degree of freedom in device design. We have developed an in situ technique for composition determination in InAsP and have shown that InAsP/InP (100) strained multiple quantum wells exhibit quantum-confined Stark effect in the 1.3 micrometers region. The existence of an internal piezoelectric field in InAsP/InP (111)B strained single quantum wells is demonstrated by the blue energy shift from carrier screening in photoluminescence spectra.

We investigate the optical properties of (h11) and (110) InAs/GaAs heterostructures with built- in piezoelectrical fields. In both cases we find that the lateral structure of the quantum wells can decisively enhance the impact of the internal electric fields on their optical properties. In the first case this is due to the local screening of piezoelectric fields. In the second case it is the result of artificially introduced lateral piezofields. Both concepts open the way to a new class of semiconductor heterostructures with strong optical nonlinearities.

InAs/InGaSb strained-layer superlattices have been deposited for long wavelength infrared (IR) detectors. The superlattice structure consists of alternating periods of InAs and InGaSb deposited upon GaSb or GaAs substrates. The lattice mismatch between the two layers is accommodated by strain which modifies the electronic and optical properties of the material. These properties can be controlled by varying the layer thickness, composition, and heterointerface properties. Molecular beam epitaxy was used to deposit the InAs/InGaSb superlattice and reflection high energy electron diffraction (RHEED) patterns were observed during growth. It was found that RHEED oscillations and x-ray diffraction patterns were heavily influenced by the incident As₂ flux used during the InAs layers. Precise control of the As flux with a valve cracker resulted in RHEED intensity oscillations continuing throughout the superlattice and excellent x-ray diffraction patterns. Fast Fourier transform IR spectroscopy of the superlattices indicate absorption around 13 micrometers .

The surface morphology and degree of strain relaxation in compositionally graded In_xGa_1-xAs epilayers grown on GaAs substrates can be controlled by the growth conditions. In_xGa_1-xAs epilayers grown as compositionally step-graded buffers on (001) GaAs by solid-source molecular beam epitaxy at a constant substrate temperature and GaAs growth rate (>= 500 degree(s)C, 0.9 micrometers /hr) undergo a transition from two to three dimensional morphology as the indium concentration is increased from x equals 0.3 to x equals 0.4. The strain relaxation is asymmetric in the <110> in- plane directions and severe roughening with the formation of cusps occurs preferentially in the (110) direction. When the substrate growth temperature is lowered successively for each InGaAs composition and the Ga beam flux lowered for the growth of the x equals 0.4 layer, the surface morphology becomes two-dimensional and the strain relaxation symmetric and greater than 90% in the two <110> directions.