GexSi1-x layers (0 ≤ × ≤ 1), with thicknesses ranging from 0.1 to 1.2 µm, were grown on Si(100) and Si(lll) by chemical vapor deposition (APCVD, LP/RTCVD) and liquid phase epitaxy (LPE), respectively. A NanoTest 500 machine served for nanoindentation measurements to evaluate the hardness and elastic moduli. The GeSi layers show strong alloy hardening with an increase varying proportional to x(l-x) as reported for III-V and H-VI-semiconductors. Maximum hardness is close to x = 0.45 at one and a half of the silicon hardness. For binary alloys such as Ge-Si, which show complete solid solubility, the elastic moduli are generally assumed to vary linearly with composition. In contrast to that we found for the indentation modulus E/(l-v2) a positive deviation of 30 % from linear interpolation (Vegard’s law), proportional to x(l-x). The increase in the elastic constants is explained by the structural properties of the Ge-Si alloy.

In situ substrate curvature measurements obtained during isothermal annealing of Si1-xGex films grown on (001) Si substrates allow determination of the evolution of strain versus time in these films. By coupling the strain relaxation measurements with previous measurements of dislocation velocities in this system, the mobile threading dislocation density and its evolution in the course of strain relaxation can be determined. The results indicate that in the late stage of strain relaxation, the mobile threading dislocation density decreases significantly. Results obtained with samples of two different sizes show that this decrease in mobile dislocation density is not primarily associated with dislocations running out at the edges of the film but with dislocation interactions impeding their further motion. Furthermore, for films thinner than 500 nm the residual strains after annealing are significantly higher than the values predicted by the equilibrium theory of misfit dislocations. The measured residual strains are compared with predictions based on Freund’s treatment of the blocking of a moving threading segment by an orthogonal misfit dislocation in its path. We find that the blocking criterion gives a very good account of the residual strain in Si1-xGex films and that blocking of threading dislocations by other misfit dislocations appears to play an important role in the late stage of strain relaxation.

When a half-rectangular perfect or partial dislocation loop is emitted from the surface of a strained epilayer, the optimum dislocation shape occurs at a saddle point of the total energy profile as a function of the dislocation width and length. The activation energy and the optimum shape are calculated for either a compositionally graded or uniform epilayer. The results indicate that 1) dislocation emission is more difficult in a compositionally graded layer than in a compositionally uniform layer; and 2) the ratio of threading dislocation density to mismatch dislocation density is lower in a compositionally graded layer than in a compositionally uniform layer. Theoretical results agree with experimental observations [1,2].

A phenomenological lattice dynamics model has been developed that describes how strain affects phonon frequencies and elastic constants in Group IV and III-V semiconductor thin films and strained layers. Using this model, the phonon dispersion relations for strained-layer heterostructures of Ge and GaAs on Si have been obtained in the quasiharmonic approximation. This model uses available experimental data and can predict the effect of arbitrary strains on thin films.

Epilayers of LPE Cdo.24Hgo.76Te grown on (111)B CdTe and Cdi-xZnxTe substrates have been examined by defect etching and triple axis x-ray diffraction. Defect etching of bevelled layers has shown the threading dislocation density to fall with increasing distance from the heterointerface, for distances <6μm. In thicker regions however a constant ‘background’ dislocation density is observed. Background dislocation densities of ∼ 3 x 105cm-2 and 9 x 104cm-2 have been measured for layers grown on CdTe and Cdo.96Zn0.04Te respectively, this is compared with a substrate dislocation density of ∼ 3 x 104cm-2 measured in both types of substrates. The increase in the dislocation density within the epilayers compared with the corresponding substrate is discussed. An explanation is also given for the displacement of the peak dislocation density, from the interface to within the layer, observed in the Cd0.76Hg0.24Te / Cd0.96Zn0.04Te system.

We have grown epitaxial GaN thin films on A1N buffered Si(lll) by radio frequency glow discharge sputtering. GaN growth direction strains and GaN E2 optical phonon energies are measured. At the same growth temperature, plasma potentials of the radio frequency glow discharge in which GaN is grown, GaN growth rate, and strain in GaN increase systematically as a function of increasing input power. The measured GaN E2 optical phonon energy scales with GaN lattice strain. Our results indicate the presence of significant intrinsic stresses in epitaxial GaN films and point to the importance of plasma characteristics in controlling the physical properties during plasma assisted thin film deposition.

X-Ray Transmission and Reflection Topography settings have been used to perform stress and strain measurements in the epitaxial system GaAs/Ge : radius of curvature of the whole sample is obtained from the Lang (transmission) set-up ; tetragonal distortion in the layer is deduced from the Berg-Barrett (reflection) setup. Comparison of these results and correlation with dislocations densities estimated from topographs enable the elastic state of the system to be known.

Si/Si0.8Ge0.2/Si(001) structures were grown at various growth temperatures (250 ∼ 760 °C) using molecular beam epitaxy, and the variation of strain and microstructure of the film was investigated using double crystal X-ray diffractometry and transmission electron microscopy. SiGe films with good single crystallinity were obtained at the growth temperatures of 440 ∼ 600 °C. For the samples grown below 350 °C, an amorphous SiGe film was developed over the SiGe single crystalline layer with a jagged amorphous/crystalline (a/c) interface, and many defects such as stacking faults and microtwins were formed below the a/c interface. Dislocations were developed through out the films for the samples grown above 680 °C. In addition, for the samples grown below 680 °C, the amount of in-plane strain of the SiGe film was found to be about − 8×l0−3 without strain relaxation. However, the SiGe films grown at 760 °C have small in-plain strain of − 4×l0−3 and large strain relaxation of 50%.

The effect of elastic constants on the critical thickness of an epilayer is investigated. The results indicate that the self energy of the dislocation is controlled by the soft phase between the epilayer and the substrate, while the interaction energy only depends on the elastic constants of the epilayer. It is easier for a dislocation to be formed if the substrate is softer than the epilayer, and consequently the critical thickness is smaller. On the other hand, a soft epilayer can have a large thickness without any mismatch dislocation.

Research of the strain effect on semiconductors and their heterostructures has generated increasing interests due to its important device applications. We have developed a eutectic bonding technique to create in-plane anisotropic strain in GaAs/AlGaAs multiple quantum well (MQW) thin films. MQW thin films grown on (100) GaAs substrates were bonded to (100) GaAs, (100) Si and Y-cut LiNbO3 submounts with a Au/Sn eutectic alloy. The bonding materials consist of Au/Sn multilayer (80 wt% Au and 20 wt% Sn; 0.95μm) with a Cr (500Å) adhesion layer. The bonding process was optimized by carefully choosing the annealing conditions. After bonding, the substrates of the MQWs were removed by wet chemical etching. The in-plane strain was induced in MQW thin film due to the different thermal expansion between the thin film and submount. The strain was characterized using X-ray rocking curve. The microstructures of bonding interfaces and MQW thin films were examined by scanning electron microscope(SEM) and cross-section transmission electron microscope (XTEM). This bonding technique can be used for many new device applications which take the advantage of in-plane strain, as well as for device integration.

The influence of growth conditions on structural perfections and epitaxial relation in BaF2 films on Si(111) are considered. It is shown that rotational-twin-free BaF2 films (A-type orientation) can be grown on Si(111) by two step growth method. It is also shown that a mixed (A+B)-type orientation, which usually observed in BaF2 films grown by conventional one step growth method, can be converted into A-type orientation by postgrowth annealing. The correlation between type of epitaxial orientation in BaF2 films and structures of interface is discussed.

Ag/Cu multilayers are deposited onto a thin Si(100) cantilevered substrate in ultra high vacuum. During deposition, the force per unit width (F/w) in the multilayers is measured continuously from the substrate curvature by a laser scanning technique. Mechanical stability and sample temperature are monitored continuously. The evolution of stress in the film during a layer deposition depends on the thicknesses of the layers beneath it. During deposition of thicker layers of either Cu or Ag, we observe increasing tensile F/w at the start of each layer. The F/w increases up to a few N/m at ∼20 nm layer thickness, and then decreases. When the thickness of each layer is less than 30 nm, the tensile stress sometimes continues to decrease even after a new interface is created. This result does not support a model for the origin of compressive stress that is based on coherent propagation of compressive strain.

This study investigates methods of predicting the deformation and stress distribution in multilayer optical thin film structures. The thin film layers include materials of various thermal expansion coefficients, elastic moduli, and melting temperatures. Each layer is deposited at a different temperature, causing complex thermal and deposition stresses throughout the structure. In addition, since the deposition temperatures of some of the layers are high (>600°C), stress relaxation and plastic flow may occur in materials with low melting temperatures. A combination of theoretical predictions and experimental measurements is used to measure and quantify the deformation caused by residual and thermal stresses in the films as well as any plastic deformation that may have occurred. Results from a model using multilayer plate bending theory to determine the elastic deformation of the device due to thermal stresses are reported. These predictions, as well as a more common method of predicting film stress and curvature, are compared to experimentally measured curvature changes as a function of temperature in the samples. However, when plastic deformation begins to occur at high temperatures, the residual stress and degree of deformation are no longer predictable based on elastic theory alone, and have to be measured experimentally. Plastic deformation in the substrate is discussed as a cause of a high observed curvature following sample heating.

Experiments were conducted on multilayer thin films to determine the free energies associated with silver/iron interfaces. Creep studies determined the loads for which the multilayers neither shrank nor stretched over time. Microstructural data was used with the zero creep loads in a model for grain boundary diffusion controlled creep in multilayers to determine the interfacial free energy.

Metallic multilayer thin film structures exhibit very high hardnesses. The epitaxial Ag/Cr system was chosen to investigate the mechanisms responsible for these high hardnesses. The interfaces of this multilayer structure are expected to be chemically abrupt since silver and chromium are nearly immiscible and do not form intermetallic compounds. The crystallographic structure formed by epitaxial growth isolates the slip systems of each layer.

The samples were deposited on (001) MgO substrates by sputter deposition at room temperature. The bilayer spacing of the samples ranges from 1 nm to 20 nm. X-ray diffraction results indicate that the multilayer films exhibit the rotated (001) crystal structure. Hardness and indentation modulus were measured by depth-sensing indentation experiments using a Nanoindenter. The maximum hardness is roughly four times the weighted average of the single component films. The indentation modulus at small bilayer periods varies by ±15% from the value at large bilayer periods, but all of the values fall between the moduli measured for the single component films.

Decreasing the bilayer period increases the hardness. At bilayer spacings smaller than 4 nm, the hardness remains constant. Decreasing the thickness of the Cr layer while keeping the thickness of the Ag layer at 5 nm, increases the strength of the multilayered film. At Cr thicknesses smaller than 5 nm, the hardness decreases as the Cr thickness decreases. The effect of the volume fraction of Cr on film strength was also studied.

The results are discussed in the context of a deformation model in which the dislocations responsible for deformation are constrained to move in the individual layers. From this model, a lower bound on the strength of the multilayered film can be calculated if plastic deformation occurs in only one layer. An upper bound can be calculated if plastic deformation occurs in both layers. The data fall between the upper and lower bounds and lie closer to the lower bound.

The hardness dependence on the composition modulation amplitude of electrodeposited Cu-Ni multilayered thin films was investigated. The composition modulation amplitude was reduced by annealing the films, resulting in interdiffusion between the Cu and Ni layers. The hardness enhancement ΔH over that for a completely intermixed film was measured as a function of composition modulation amplitude A. It was found that for films with a sine wave composition profile, the hardness enhancement ΔH varied as A1.1±0.1, in good agreement with the model given by Krzanowski [1].

The hardness of epitaxial sputter-deposited Fe(001)/Pt(001) multilayers grown on single crystal MgO(001) has been previously evaluated as a function of composition wavelength, Λ. Nanoindentation results reveal that the hardness is enhanced over that expected from a simple rule of mixtures by a factor of approximately 2.5 for bilayer spacings from 20 to 125 Å. In this paper we investigate possible causes of this hardness enhancement by determining the stress, strain, and alloying in each layer of the multilayer as a function of Λ. Accurate in-plane and out-of-plane lattice parameter measurements were obtained via x-ray diffraction using synchrotron radiation. The stress state and the extent of alloying in each layer as a function of Λ was determined by using the appropriate elastic constants for each component. The stress, strain, and amount of alloying in the Pt layer were near zero for 25≤Λ≤121 Å. The Fe layer exhibited large stresses and strains which relaxed with increasing Λ for 44≤Λ≤121 Å. For Λ=25 Å, the metastable FCC structure was adopted by the Fe film. The amount of alloying also varied from approximately 11 at.% Pt for Λ=44 Å to 5 at.% Pt for Λ=121 Å. Since the structure, film stress, amount of strain relaxation, and extent of alloying vary over this range of Λ while the hardness does not, we conclude that the hardness enhancement in these films must be controlled by other factors. Nevertheless the investigation of these basic film properties has enhanced our understanding of the structure-property relationships that give rise to strengthening in multilayer thin films.

Au(100)/Ni(100) periodic superlattices have been grown by the MBE technique specially for X-ray diffraction experiments. The nominal number of Ni planes deposited were 1.5, 2, 4 and 5 ML and the thickness of the gold layers was always 1.5 nm. The X-ray profiles have been simulated using a kinematical structure refinement program. The obtained strain profiles are in very good agreement with earlier HREM results. It is shown that a strong interdiffusion occurs during the growth.

The Brillouin light scattering technique has been exploited for investigating the elastic properties of periodic superlattices made by alternating layers of Ta and Al. These multilayers, deposited by d.c. sputtering on glass and Si substrates, present a polycrystalline structure with (110) and (111) texture for the Ta and Al layers, respectively. They have total thicknesses of about 0.5 μm and periods ranging from 4 to 10 nm. Measurement of the phase velocities of the Rayleigh and Sezawa acoustic modes from the frequency position of the corresponding Brillouin peaks, yielded informaton on the effective elastic constants of the superlattices. for large periods (8-10 nm) the values determined experimentally are in good agreement with those calculated from the elastic constants of the bulk materials, while for lower periods (4-6 nm) the estimated elastic constants exhibit a marked increase. This anomalous behavior has been attributed to the presence of a transition layer at each interface, where Ta and Al interdiffuse, as observed by x-ray and electron microscopy experiments.

The mechanical properties of thin-film Cu/Cu-Ni and Cu/Ag multilayers are examined in this study. Films were prepared by magnetron sputter deposition onto cleaved NaCl substrates. The use of a computer-controlled deposition system enabled the multilayer interface width to be varied, as well as the multilayer amplitude and bilayer thickness. The Cu/Cu-Ni multilayers had the form of (001) oriented single crystal films, but for Cu-Ag multilayers only polycrystalline films could be obtained in the (001) orientation. For Cu/Cu-15%Ni multilayers, the tensile strengths were measured and observed to increase with decreasing interface width at constant wavelength. Tensile strengths were also found to increase with increasing composition modulation amplitude. For films with constant interface width but bilayer thicknesses ranging from 10 to 60 nm, the tensile strength was relatively constant. The results are consistent with previous theoretical treatments, particularly the theory of modulus hardening.