High-resolution X-ray Diffraction Rocking Curve Research Articles

GSMBE growth and characterization of strained-layer MQWs in a P-i-N Configuration

InxGa1-xAs/InP (0.39 less than or equal to x less than or equal to 0.68) strained-layer quantum wells having 20 wells with thickness of 50 Angstrom in a P-i-N configuration were grown by gas source molecular beam epitaxy (GSMBE). High-resolution X-ray diffraction rocking curves show the presence of up to seven orders of sharp and intense satellite reflection, indicative of the structural perfection of the samples. Low-temperature photoluminescence and low-temperature absorption spectra were used to determine the exciton transition energies as a function of strain. Good agreement is achieved between exciton transition energies obtained experimentally at low temperature with those calculated using the deformation potential theory.

Strain and relaxation effects in InAsP/InP multiple quantum well optical modulator devices grown by metal-organic vapor phase epitaxy

Strained-layer multiple quantum well (MQW) InAsP/InP optical modulators have been fabricated from layers grown by metal-organic vapor phase epitaxy. The devices are a series of p-i(MQW)-n photodiodes in which the active core regions consist nominally of 25 periods of 10 nm InAsP quantum wells of 4.4%, 10.0%, 15.6%, and 26.4% As composition separated by 10 nm InP barriers. Structural parameters for the samples were obtained using high-resolution x-ray diffraction rocking curves and transmission electron microscopy. The series contains samples with both coherently strained and partially relaxed multi-layers where the relaxation is characterized by misfit dislocations. The band offsets for the heterostructures were determined by fitting the energy positions of the optical absorption peaks with those computed using the Marzin–Bastard model for strained-layer superlattices [as in M. Beaudoin et al., Phys. Rev. B 53, 1990 (1996)]. The conduction band discontinuities thus obtained are linear in the As composition (7.56±0.08 meV per As % in the InAsP layer) at low and room temperature for As concentrations up to 39%, and up to 17% average relaxation. Comparisons between the coherently strained and partially relaxed samples demonstrated a broadening of optical transition linewidths due to relaxation which appears to be of minor consequence for optical modulator devices as the essential optical and electrical properties remain intact. The electric field-dependent red-shift of the n=1 electron-heavy hole transition was measured by a photocurrent method and found to be enhanced in structures with lower barrier heights.

High-resolution x-ray diffraction measurements of residual stresses in polycrystalline thin films deposited on single crystalline substrates

A nondestructive method for stress determination in polycrystalline/amorphous thin films deposited on the nearly perfect crystals was developed. High-resolution x-ray diffraction rocking curves are taken from the substrate using a monochromatized and quasiparallel incident x-ray beam. Changes in the rocking curve shape, caused by stress-induced bending of the substrate, are compared with the newly derived analytical expression of the diffraction spectrum, and as a result the radius of curvature and hence the biaxial stress is obtained. For the (004) Si reflection and the Cu Kα1 radiation the radii of curvature within the interval, 3 m<R<500 m, can be resolved. The method was successfully applied to measure stresses in heat-treated Ni90Ti10 alloy films deposited on a Si (001) substrate. The stress behavior (as a function of the annealing temperature) was found to reflect the sequence of the formation of silicides and enabled the evaluation of their thermal expansion coefficients.

Growth studies of GaP on Si by gas-source molecular beam epitaxy

We report a growth study of GaP films grown by gas-source molecular beam epitaxy on Si substrates oriented 4° off (100) toward [110]. Reflection high-energy electron diffraction (RHEED), high-resolution X-ray diffraction rocking curve (XRC), and scanning electron microscopy (SEM) were used to characterize material quality. Growth studies were carried out in terms of the growth temperature, V III ratio, and GaP film thickness. Two different growth methods were used: one-step direct growth and two-step growth, i.e. a thin GaP layer is grown first at a relatively low temperature as a buffer layer, followed by the main GaP layer grown at the normal growth temperature. The results show that with the two-step growth, the material quality of GaP can be greatly improved. Investigation of the effect of using different prelayers (As 2, P 2, Al, Ga, and Ga + Al) on the quality of GaP films reveals that the Ga prelayer gives the best result. By optimizing the growth conditions, GaP films with very smooth surfaces were obtained.