GaAs-like Longitudinal Optical Phonon Research Articles

Atomic Force Microscopy and Raman Spectroscopy Study of Strain Relaxation in InGaAs ON GaAs(100) Grown by Chemical Beam Epitaxy Using Unprecracked Monoethylarsine

The correlation of surface morphology with strain relaxation in the In0.15Ga0.85As epilayer on GaAs(100) grown by chemical beam epitaxy using unprecracked monoethylarsine has been investigated. The surface morphology of InGaAs was analyzed by atomic force microscopy as the epilayer thickness was increased from 0.025 to 1.668 μm. The changes in the surface morphology indicated that surface roughening is related to the process of strain relaxation in the film. The strain-induced shifts in the GaAs-like longitudinal optical phonon in the Raman spectrum also indicated that the strains in the InGaAs epilayer relax via step-wise process with increasing the film thickness beyond the critical thickness, which agrees well with the changes of surface mophology.

Defect and strain redistribution in InxGa1−xAs/GaAs multiple quantum wells studied by resonant Raman scattering

Resonant Raman scattering by longitudinal optical (LO) phonons in the GaAs barriers of InxGa1−xAs/GaAs multiple quantum well structures has been used to study the onset of strain relaxation as the number of quantum wells is increased. The intensity of scattering from one and two GaAs LO phonons for excitation in resonance with the GaAs E0+Δ0 band gap is found to be highly sensitive to the formation and/or redistribution of defects and the buildup of strain in the barriers, and thus to strain relaxation in the InxGa1−xAs quantum wells. This behavior allows us to detect the onset of strain redistribution, even in samples where the frequencies of both the GaAs LO phonon in the barrier layers and the GaAs-like LO phonon in the InxGa1−xAs quantum wells show no measurable shift. Here, the GaAs LO phonon frequency observed in structures with fully strained InxGa1−xAs wells and unstrained GaAs barriers is used as a reference.

Raman scattering of InGaAs/InP grown by uniform radial flow epitaxy

Uniform radial flow epitaxy, a novel growth technique, has been used to grow InGaAs films on InP. Epitaxial layers above and below the critical thickness for the onset of slip were grown. We used Raman spectroscopy to characterize the quality of epitaxial layers, determine alloy composition, and measure the strain. Raman spectra from both pseudomorphic (strained) and relaxed (unstrained) InGaAs films were obtained at 300 and 80 K. The difference in the frequencies of their GaAs-like longitudinal optical phonons was used to calculate stress for the strained InGaAs/InP, leading to a direct formula for the evaluation of the layer stress.

Raman scattering from GaAs-In xGa 1− xAs strained-layer superllatices

Measurements of Raman scattering were performed on GaAs-In x Ga 1− x As strained-layer superlattices, grown by molecular beam epitaxy, with lattice periods ranging from 30 ∼ 250 Å and In concentrations x, 0.22 and 0.37. Only one GaAs-like longitudinal optical phonon peak was observed in each strained-layer superlattice, in contrast to the well-known result that two peaks were observed in GaAs-Al x Ga 1− x As superlattices. The GaAs-like phonon frequencies shifted from those of bulk GaAs to those of bulk In x Ga 1− x As alloys as the ratio of the one-layer thickness of In x Ga 1− x As to the lattice period increases from zero to one. We conclude that the GaAs-like phonon mode is a uniform mode of the whole strained-layer superlattice and the phonon frequency is determined by the averaged In concentration.