Epitaxial RSi2−x (R = Y and Er) has been grown on (111)Si by solid phase epitaxy in ultrahigh vacuum deposited metal thin films on silicon. The evolution of vacancy ordering and defect structure in epitaxial YSi2−x. and ErS2−x thin films on (111)Si have been studied by both conventional and high resolution transmission electron microscopy.

Superlattice spots located at ⅓{2110} in [0001]RS2−x, diffraction patterns are attributed to the formation of ordered vacancy structure in the Si sublattice planes. The splitting of extra diffraction spots is correlated to the formation of an out-of-step structure. Streaking of the split diffraction spots in the diffraction pattern is attributed to the presence of an out-of-step structure with a range of M values. The M was found to settle down to a fixed value after high temperature and/or long time annealing.

Planar defects in RSi2™x films were analyzed to be stacking faults on {1010} planes with ⅙<1213> displacement vectors. Computer simulation was carried out to model the atomic structure of stacking fault in YS2−x-. thin films. The simulated images are seen to match rather well with experimental images taken under two different values of defocus.

The interdiffusion in MBE-grown Si/Si1−xGex superlattices was measured by Rutherford backscattering spectrometry. The superlattices consisted of 5 periods of 100 !A Si and 100 !A Si1−xGex layers with Ge concentrations, x, between 0.20 and 0.70. Both, asymmetrically strained superlattices, grown on Si(100), as well as symmetrically strained superlattices, grown on relaxed Si1−y.Gey buffer layers were investigated. Rapid thermal annealing in the temperature range between 900°C and 1125°C leads to significant interdiffusion between the individual layers, indicated by a decrease of the amplitudes of the backscattering spectra. Interdiffusion coefficients were deduced using a Fourier algorithm. The interdiffusion coefficients follow an Arrhenius law for a given Ge concentration. The interdiffusivity increases significantly with increasing Ge concentration.

We have studied the deposition of GexSi1−x layers on (100) Si substrates by gas source molecular beam epitaxy (GSMBE) using disilane and germane.

The investigation of RHEED intensity oscillations during growth reveals the well known rate enhancement obtained when adding a small amount of germane to the disilane flux. However, when exposing a previously deposited Ge layer to a pure disilane flux the growth rate during the first few monolayers remains at an enhanced value but returns to its homoepitaxial value after about 10 to 15 monolayers. This behaviour was observed under a variety of growth conditions. It is in marked contrast to the experience obtained in conventional Si/Ge MBE and suggests a catalytic effect of the particular surface present during GSMBE growth. We propose that this effect is caused by the surface segregation of Ge species and leads to a smear-out of the Ge profile in the layer.

We investigate the formation of inAs-rich layers at the interface between InP and arsenicbased Ill-V alloys grown by chemical beam epitaxy (CBE). In-situ spectroscopic ellipsometry, low temperature photoluminescence, secondary ion mass spectrometry and transmission electron microscopy were used to characterize the formation of these layers. We present evidence for interfacial layer roughness that depends strongly on growth temperature and on the presence of surface steps, and show that modifications of the interface chemistry and of the gas-switching sequence can reduce interfacial layer thicknesses.

High resolution transmission electron microscopy (HRTEM) has been applied to study the atomic structure of NiSi2 /(001)Si interface. Previous HRTEM result suggested that Ni atoms in the boundary core are six-fold coordinated and Si atoms are everywhere tetrahedrally coordinated. In this work, high resolution imaging technique and computer image simulation were used to study the atomic structure of NiSi2 /(001)Si interfaces and a new interface structure was found. For the new interface structure, Ni and Si atoms are also six-fold and tetrahedrally coordinated, respectively, with an extra layer of fourfold planar bonded Si atoms present at the interface.

Heteroepitaxy of Sil−x Gex alloy layers on Si(100) and Si(111) has been achieved using Pulsed Laser Induced Epitaxy (PLIE). The energy of 1-50 pulses from a spatially homogenized XeCl excimer laser is used to melt a structure of electron beam evaporated Germanium on Silicon substrates. On Si(100) substrates alloys with Germanium fractions between 6 and 22% are investigated and exhibit very good crystallinity, as confirmed by MeV-Ion Channeling along the <100> - direction. Heteroepitaxy on Si(l11) yields similar results. MeV-Ion Channeling is also used to determine the level of strain in the layers. This is done by comparing angular yield curves around the <110> - direction for substrate and alloy layer. The obtained strain values are close to calculations for an ideally strained layer state. The strain is also measured for layers that have been subjected to different thermal cycles. As a result of this, predictions of feasibility for subsequent device fabrication can be made for the layers.

The Orientation control of (Ca,Sr)CuO2 film has been investigated under various sputtering conditions from the view point of controlling the “self-texture” and epitaxy. The films with (001), (110) and (101) orientations were able to be obtained by changing partial gas pressure during sputtering. These orientations were observed on glass and MgO(100) single crystal substrates. The cohesive energy between the film and the MgO single crystal substrate was calculated to evaluate the change in orientation on glass and MgO substrates.

GaSe layers were grown on the van der Waals (0001) planes of WSe2 (van der Waals epitaxy). The substrate (0001) plane was cleaned in UHV by heating to 400°C. GaSe was deposited from resistively heated Knudsen cells at T=300° C. After annealing at 450°C an epitaxial GaSe overlayer is formed as evidenced by X-ray diffraction, scanning tunneling microscopy, low energy electron diffraction and photoelectron spectroscopy.

ZnO film has a tendency to grow parallel to the <0001> axis. Therefore, it is difficult to obtain epitaxial or oriented films with any other orientation. Nevertheless, we obtained excellent epitaxial (1120) ZnO films on R-cut, (0112), sapphire by controlling the self-texture. Epitaxial (1120) ZnO on R-cut sapphire exhibits an anisotropic misfit at the interface. To clarify the growth mechanism, the stress relaxation was calculated by measuring the curvature of the substrate and the lattice spacings. The change in stress calculated by these two methods differs from each other. We discuss this discrepancy in terms of the growth mechanism.

Photoluminescence (PL) spectroscopy, cathodoluminescence (CL) spectroscopy and imaging, transmission electron microscopy (TEM), and preferential defect etching and optical microscopy have been used to characterise dislocations in plastically deformed Si and in Si1−x Gex alloys. The PL spectra from plastically deformed Si produced under clean conditions, contained no dislocation related luminescence features. However, after deliberated Cu contamination and annealing, the PL spectra were dominated by the four main D-bands (D1-D4). CL spectroscopy and imaging revealed that the D3 and D4 bands originate on the slip lines, whereas D1 and D2 are dominant between the slip lines. Pseudomorphic Si1−x Gex layers grown by molecular beam epitaxy (MBE) and forced to relax by Cu contamination and annealing have also been examined. Both the PL and CL spectra were dominated by the D1-D4 bands, and monochromatic CL imaging showed that the D3 and D4 bands originate at the misfit dislocations with the location of the Dl and D2 bands being much less well defined. PL spectra from Si1−x Gex capping layers, grown by MBE on linearly compositionally graded buffer layers, were dominated by bound exciton luminescence features, identical with those observed in bulk grown alloys, and showed relatively weak D-band features. PL spectra obtained after chemical step etching, and CL spectra obtained with different beam energies, showed that the D-bands originated in the buffer layers which contained high densities of misfit dislocations. Well defined monochromatic CL images of the misfit dislocations could only be obtained using a narrow band pass filter centred on the D4 band. No D-band luminescence was observed from Si1−x Gex layers grown by high temperature chemical vapour deposition (CVD). However, after deliberate contamination with Ni, the D-bands became the dominant features and CL imaging clearly showed that the D4 band originates at the misfit dislocations and the D2 band predominantly between the misfit dislocations.

We have developed a femtosecond ellipsometer by incorporating ellipsometric probe optics into a rapid scan femtosecond pump-and-probe experiment. The system allows near real-time display of the photo-induced reflectivity changes and provides complete characterization of the time-varying dielectric function. This ellipsometer is used ex situ to characterize the femtosecond response of relaxed, MBE-grown SixGe1−x alloys over the complete composition range. The results show. that the femtosecond response depends strongly on alloy composition in optically thick samples. Ge-like samples (x<0.37) show a characteristic two-component response which may be caused by intervalley L →Γ hole scattering and impact ionization. For a given alloy composition, the presence of interfacial strain or surface oxidation strongly alter the femtosecond response.

Lattice mismatched InxGa1−xAs layers with InAs mole fractions below 0.25 grow in a two dimensional growth mode on GaAs. If the thickness of these layers is beyond the critical layer thickness the strain relaxes through misfit dislocations. The misfit dislocation density in the <011> and <01-1> direction differs for n-type layers. This results in a highly anisotropic electron mobility for GaAs/InxGa1−xAs/Al0.3Ga0.7As inverted HEMT structures. A higher electron mobility in the < 011 > direction is measured in comparison to the <01-1> direction. The resistance ratio in the two perpendicular directions exceeds 105. For a three dimensional growth mode, the InxGa1−xAs layer shows interface roughness which degrades the transport properties of the normal Al0.3Ga0.7As/ InxGa1−xAs/ GaAs HEMT structures more than the inverted GaAs/InxGa1−xAs/ Al0.3Ga0.7As HEMT structures. For a three dimensional growth mode, an anisotropic electron mobility for Al0.3Ga0.7As/InxGal, As/GaAs HEMT structures is also observed. For these structures the highest electron mobility is measured in the < 01-1 > direction. This anisotropy could be explained by anisotropic growth rates in the <011> and < 01-1 > directions which results in growth islands with asymmetric extensions.

The correlation of low temperature electrical transport with the evolution of heteroepitaxy and morphology for sputtered indium nitride thin films has been studied. A series of indium nitride films were deposited at temperatures ranging from 50 -650 °C by reactive rf magnetron sputtering onto the (00.1) face of sapphire. Above 350 °C, a transition occurs from a continuous morphology, in which grains are in intimate electrical contact, to an open, porous morphology with poor electrical contact. This transition in morphology deeply affects the electrical transport of the semiconductor. At low deposition temperature, the electrical transport is dominated by the relatively weak intergrain scattering leading to films with moderate mobility. As the deposition temperature is raised, the increasingly porous nature of the film leads to a deterioration in electrical mobility. It is proposed here that the relevant physics of these films is analogous to that for granular solids with a distribution of electrical connectivities that suggests a scattering potential dominated by disorder. In fact, the temperature dependence of the resistivity is found to be analogous to that observed in disordered and amorphous materials. In particular, the resistivity is characterized by: 1) A very weak temperature dependence; 2) The observation of a resistance minimum; and, 3) A steep rise in the low temperature (<4K) resistivity that follows a T1/ dependence.

Lattice parameters and crystal orientation for Fe1 6.N2 were determined by an X-ray diffraction method using a three axes goniometer. The lattice parameters of the a-axis and c-axis(a0, c0.) are 5.71 !A and 6.33 !A, respectively. The co corresponds to that of In0, 2,Gao.,s As substrates. Crystal orientation between Fe1 5.N2. films and Ino.,2Gao.,8 As is Fe1 0N2(001)//In0 2.Ga0.2 As(1001) and Fe1 0.N2.(100)//In02Ga0.6As(100). Intensity ratios for these diffraction peaks are in good agreement with calculated values proposed by Jack.

The real crystal structure of In0.52A10.48As layers grown on InP<001> substrate as a function of the growth temperature (between 150°C and 450°C) was investigated. The following structural / electrical analyses were applied to the samples: transmission electron microscopy (TEM), x-ray diffraction and particle induced x-ray emission (PIXE). In the temperature range between 200°C and 450°C good epitaxial growth of InAlAs layers can be achieved with a low density of dislocations and stacking faults. Ordering of group-III elements on {111} planes was observed for these layers. Structure models of such ordered domains are discussed. At growth temperatures below 300 °C additional As (≈2%) is incorporated in the lattice. Growth at temperatures below 200°C leads to the formation of pyramidal defects with As grains in their cores. As-grown as well as annealed InAlAs layers show a nearly constant, high electrical resistance (106-107Ωcm) in the whole temperature range.

Optical absorption measurements have been carried out on compressive InGaAs/FInP strained layers. It is shown that thoptical absorption analysis is a powerful technique in order to study the inhomogeneities of strained layers. The energetic dispersion of the heavy hole relative to the light hole subband σHH/σLH is related with the presence of the coarse structure seen in Transmission Electron Microscopy observations.

A cantilever shadow masking technique has been used for the first time to grow CdTe in recesses of GaAs wafers. The use of this technique eliminated the deleterious effects of side wall growth. Scanning electron microscopy, electron channeling, Auger spectroscopy and photoluminescence were used to characterize these structures. An application to planar monolithic infrared focal plane arrays is discussed.

We report on the growth and characterization of multiple quantum well structures by UHV/ CVD epitaxy. X- ray diffraction is used to verify the expected layer periodicity and to determine the quantum well thickness. Photoluminescence measurements show peaks which we associate with recombination of excitons in the quantum wells. The measurements are consistent with high quality layers with small variation in quantum well thickness across a wafer.

It has been recently shown that high quality ZnSe and ZnTc filns can be grown on GaAs using low temperature growth techniques such as Metal-Organic Chemical Vapor Deposition ( MOCVD). All samples: ZnSe, ZnTe, ZnSc(l−x)Tc(x) epilayers and ZnSe/ZnTc superlattices were grown using a novel zinc precursor, the Tri-Ethyl-Amine Di-Methyl-Zinc, while we used the classical precursors H2Se and Di-Isopropyl-Tellurium for selenium and tellurium. Investigation of the photoluminescence (PL) properties of ZnSc and ZnTe single layers enabled us to optimize the growth conditions of these compounds. The crystal growth conditions for mixed alloys and superlattices were determined by direct comparison to the aspect of low-temperature PL features. Strong PL spectra were obtained from these materials, suggesting us that tellurium has the ability to behave like an iso-clectronic center. At low concentration of tellurium in ZnSe, an interesting physical situation is observed, which we have interpreted in terms of extrinsic exciton “self-trapping” mechanism.

We have investigated the electrical properties of the two-dimensional-electron-gas (2DEG) present in strain relaxed heterojunctions with InxGa1−xAs channels (x<0.4). These were grown by molecular beam epitaxy on misoriented (001) GaAs substrates using compositionally step graded buffer layers, … x' = 0.1 per step, each step 0.3 µm thick. The 2DEG is produced by modulation doping using lattice matched InyAl1−yAs as the carrier supply layer. We find typical electron densities and mobilities, for x=0.3, of ns(300 K) = 1.3 × 1012 cm−2 and µH(300 K) = 9300 cm2/V-s; and for ns(1.6 K) = 1.2 × 1012 cm−2, µH(1.6 K) = 37800 cm2/V-s. While the room temperature electron mobility shows negligible anisotropy, an <110>-orientation dependent low temperature electron mobility of the 2DEG is observed and attributed to dislocation scattering.