Intrinsic stress and microstructure of mixed composition films were investigated for several material systems useful in the IR wavelength range. Stress in coevaporated mixed films (analog) deviated from a linear dependence on composition, while in discrete alternating films (digital) it varied linearly with composition. For MgF2-Ge and CeF3-Ge, analog film stress was small and compressive over a large range of intermediate compositions despite the fact that the constituent materials had high tensile stress. The stress behavior correlated with changes in the microstructure. Low stress compositions were observed to correspond to enhanced grain size in the mixed film. These results have significant implications for the design of gradient-index thin-film structures.

The growth of epitaxial films of cerium (Ce)/vanadium (V)/on single crystal sapphires (α-A1203) was studied by in-situ reflection high energy electron diffraction and x-ray scattering. For the first time Ce(111) single crystal film was grown on V(110)/α-A12O3 (1120) in the Frank-van der Merwe mode. A new epitaxial orientation, different from the well known Nishiyama-Wasserman or Kurdjumov-Sachs orientations is found in the present study. Subsequent V(110) layers grow epitaxially with three equivalent domains.

The x value of the most thermally stable co-sputtered TaxCu1-x alloy films are found to correlate with measured maximum temperature coefficients of resistance as a function of alloy composition. To investigate the possible application of these materials as diffusion barriers for the Au-GaAs system, vacuum annealing and infrared rapid thermal annealing are made over a wide temperature range. Resistivity changes, X-ray diffraction, Auger electron spectroscopy, and Rutherford backscattering measurements are performed to find the metallurgical stabilities of these materials at elevated temperatures.

For high x values, the reaction temperature for TaxCu1-x, in contact with GaAs lies between 500 and 700°C. For Au in contact with TaxCu1-x the TaxCu1-x/GaAs reaction occurs at about 600°C. Amorphous Ta93Cu7 exhibits uniform mixing with surrounding elements, whereas Ta80Cu20 exhibits phase separation.

We have prepared, heat treated and characterized various amorphous semiconductor periodic multilayers and ultrathin films. These were prepared by several vapor deposition techniques at substrate temperatures ranging from 25°C to 300°C and possessed periodicities from 22 to 400Å. Films were subjected to isochronal thermal treatments at progressively higher temperatures. Two effects were observed: enhanced diffusion and retarded crystallization. Interdiffusion, at rates which are many orders of magnitude higher than those anticipated from crystalline data, was observed in a-Si/a-Ge multilayers. Crystallization of germanium, the more readily crystallized member of the couple, is retarded; the extent depends on the thickness of the layer. The thinner the layer, the greater the retardation. Where intermixing is thermodynamically unfavorable as in a-Si/a-SiNx or a-Ge/a-SiNx multilayers, and ultrathin germanium layers on SiO2, interdiffusion does not occur, however, crystallization of silicon or germanium is again substantially retarded.

Amorphous thin films of SixGe1-x:O (x = 0.70) were prepared by RF-sputtering at several substrate temperatures. The structural properties of these films were studied by IR spectroscopy and revealed features characteristic of hydrogen and/or oxygen bonded to silicon. The optical constants (n,k) were determined from reflection and transmission measurements at near-normal incidence for photon energies in the range of 1 eV and 2.6 eV. The optical gap was derived from the Taue plot and correlated with the composition of the samples. The increase of hydrogen and/or oxygen decreases the value of the refractive index and increases the optical gap.

We have investigated the Raman and the phonon transmission spectra of a-Si:H/a-SiNx:H super lattices. At low wavenumbers, the Raman spectrum shows sharp peaks corresponding to the excitation of modes from the folded branches of the dispersion relation for longitudinal acoustic phonons propagating perpendicular to the layers. Energy gaps in the folded phonon dispersion occur at the center and at the boundary of the mini-Brillouin zone due to the differences in the acoustic impedances of the layers. The size of the lowest gaps was determined by light scattering. The phonon transmission spectra show transmission minima that we attribute to the frequency gaps in the dispersion of transversal acoustic phonons. The position and width of these minima are compared with the dispersion obtained from the Raman data.

We have studied the optical, electrical and photoelectronic properties of a-Si:H thin films in surface cell structures. We have concluded that upward band bending in the form of depletion layers at the film surface and film oxide glass interface causes the electrical properties to display a thickness dependence. We find that the measured values of the quantum efficiency, mobility, lifetime product, hereafter nuT, also displays a thickness dependence. We show how the limiting bulk values for nuT and other electronic properties can be determined.

We have grown films of silicon oxide by remote Plasma Enhanced CVD (remote PECVD). By changing the fraction of O3 in a plasma excited O3/He mixture that is mixed with a fixed flow of SiH4 diluted with Ar, we can deposit films which are either Si-rich, stoichiometric or Si-deficient. These changes are accompanined by differences in the incorporation of bonded hydrogen which occurs in SiH groups in Si-rich films and SiOH groups in Si-deficient films.

Amorphous hydrogenated silicon-tin films (α — Six Snx:H) have been prepared by co-electron beam and Knudsen cell deposition. It is shown that the dependence of Eg on x, over the entire range of 0 < x < 0.51 studied, cannot be described by a single linear relationship. The d.c. conductivity measurements indicate two distinct conduction regions as a function of x. The addition of Sn up to x = 0.10 creates a high density of dangling bonds and moves the band edges so a significant conductivity increase is observed. The bonding between Si and H is preferred to Sn and H. Sn-H bonds were observed only for x > 0.40. Photoluminescence measurements show that band edge luminescence dominates at 1.3–1.4 eV.

The effects of chemical etching, mechanical thinning, and ion milling on the low temperature photoluminescence spectra of MBE grown (001) CdTe films are reported. Line defects observed by TEM are correlated with photoluminescence. It is shown that X-ray D.C.R.C, measurements in these films are weighted averages over the whole thickness of the films and therefore weakly reflect the structural perfection of the samples near the surface as deduced by photoluminescence.

We show that bonded hydrogen in a-Si:H is readily exchanged by atomic deuterium when exposed to a deuterium plasma discharge. The effective diffusion coefficient for the D.H exchange, 10∼14 cnr/sec at 160°C, is comparable to that of interstitial hydrogen in c-Si.

We study the interface between un-alloyed a-Si:H,F and an a-Si0.4,Ge0.6:H,F alloy using superlattice structures. From infrared spectroscopy we estimate a width of 8 A for the excess hydrogen layer, and X-ray diffraction data give us a width of 2Å contributing to the width of the diffraction peak. Vibrational Raman scattering data show that the ratios of the number of Si-Si, Ge-Ge and Si-Ge bonds is not altered by changing the number of interfaces. This fact allows us to establish an upper limit for the interface width of 3 atomic layers, i.e. one layer in each partner plus an intermediate layer.

The lifetime of photogenerated electrons in a-Ge:H/a-Si:H multilayer structures with layers about 100Å thick, is enhanced by two orders of magnitude above the value in bulk a-Ge:H. This lifetime enhancement effect is explained by charge separation produced by layers, due to the assymmetry in the conduction and valence band offsets at the interfaces. The peak in the electron lifetime as a function of superlattice periodicity is determined by a trade-off between the electron tunneling rate into the a-Si:H barriers and electrostatic repulsion of holes due to photo-induced space charge.

The optical reflectivity at 6328Å of a-Si:H, a-Ge:H, a-Si:H/a-SiNx:H and a-Si :H/a-SiOx:H interfaces can be explained by a model of chemically abrupt interfaces that are macroscopica!ly rough on a scale of 10–20Å.

We report a study of the interface formation between a-Si:H and a-SiOx:H or a-SiN:H in the coverage regime from a submonolayer to a few layers. The films were grown by plasma assisted CVD and characterized by photoemission. Our studies show that the growth mechanism is different for a-SiOx:H on a-Si:H than for a-Si:H on a a-Si:Ox:H. The growth of the a-SiNx:H/a-Si:H interface on the other hand is independent of the direction.

Experimental results on a-Si:H/a-C:H superlattices, including the blue-shift of the optical band gap, the light-induced conductivity effect, the interface structure and the interfacial defects, are presented. Differences between our glow-discharge and sputter-prepared a-Si:H/a-C:H super lat t ices are described.

Photoacoustic (PAS) and optical transmission spectra were measured on a-Si:H/a-SiNx:H superlattices. The absorption coefficient ∝ in the range 102∼104 cm-1 was obtained by converting the PAS signal to ∝. The enhancement of the PAS peak intensity Qs and the increase in the width of the Urbach edge with decreasing a-Si:H layer thickness are explained as results of quantum size effect in the superlattice structure.

We have prepared, heat treated and characterized various amorphous semiconductor periodic multilayers and ultrathin films. These were prepared by several vapor deposition techniques at substrate temperatures ranging from 25°C to 300°C and possessed periodicities from 22 to 400Å. Films were subjected to isochronal thermal treatments at progressively higher temperatures. Two effects were observed: enhanced diffusion and retarded crystallization. Interdiffusion, at rates which are many orders of magnitude higher than those anticipated from crystalline data, was observed in a-Si/a-Ge multilayers. Crystallization of germanium, the more readily crystallized member of the couple, is retarded; the extent depends on the thickness of the layer. The thinner the layer, the greater the retardation. Where intermixing is thermodynamically unfavorable as in a-Si/a-SiNx or a-Ge/a-SiNx multilayers, and ultrathin germanium layers on SiO2, interdiffusion does not occur, however, crystallization of silicon or germanium is again substantially retarded.

Steady state optical modulation spectrum of a-Si:H/a-SiNx:H multilayer structure, its temperature dependence and time decay have been studied. For multilayers with very thin sublayers the onset of the spectrum is more gradual and occurs at higher energy than the spectrum for unlayered a-Si:H, indicating a broadening of the band tail. For larger layer thicknesses the optical modulation spectrum is compared to that for P-doped a-Si:H and interpreted as due to charged dangling bonds at the interfaces.

The structural effects of heating 1500 Å Au/GaAs (001) encapsulated with 2000 Å of SiO2 were examined by scanning electron microscopy and x-ray diffraction. It was observed that SiO2/Au/GaAs (capped) in vacuum up to 500°C remained shiny and gold in color, whereas similar heating of Au/GaAs (uncapped) caused a change of color from shiny gold to dull silver. Furthermore, mass spectroscopy showed that the amount of arsenic vapor evolved was much less for the capped sample. However, x-ray diffraction showed that Au7Ga2 formed abundantly in both types of samples after heating at 500°C, though the epitaxial relationship was AuyGa2 (001) // GaAs (001) for capped and Au7Ga2 (100) // GaAs (001) for uncapped. SEM revealed gold-rich aligned rectangular protrusions on the surfaces of SiO2/Au/GaAs as well as Au/GaAs after heating at 500°C, though the average length of these rectangles was 1.5 μm for the capped sample and 6.7 μm for the uncapped sample. Moreover, new morphological features absent in Au/GaAs were observed in SiO2/Au/GaAs. These features are a gold-rich maze with a line width of 6 Åm and gold-rich protruded lines with a line width of 9 Åm. The gold-rich protruded lines were formed by the growth and joining together of some gold-rich aligned rectangular protrusions. The gold-rich maze was observed in SiO2/Au/GaAs after heating in vacuum, but was not observed in SiO2/Au/GaAs after heating in nitrogen.