Use of Raman spectroscopy to characterize strain in III–V epilayers: Application to InAs on GaAs(001) grown by molecular-beam epitaxy

Abstract

Strain in thin layers of molecular‐beam epitaxy (MBE) grown InAs on GaAs(001) was characterized by both Raman spectroscopy and double crystal x‐ray diffraction (DCD). The goal of this study was to evaluate the use of Raman spectroscopy as a method of strain determination and compare it to DCD. Recent results of Burns et al., for InxGa1−xAs proved that Raman spectroscopy could be an important in situ analysis method for MBE [G. Burns, C. R. Wie, F. H. Dacol, G. D. Pettit, Appl. Phys. Lett. 51, 1919 (1987)]. We find that Raman spectroscopy has several advantages over DCD. Raman data samples the stress in a much thinner volume than DCD, allowing one to determine when a surface layer of the thin film is no longer under stress. Films that are highly lattice mismatched with the substrate have a large number of defects at the substrate/epilayer interface. Raman analysis determines straain in a more defect free layer of these films when the layer thickness is greater than tc, the critical thickness. DCD samples an average strain over the entire thickness of most semiconductor films. There are several disadvantages in the use of Raman spectroscopy as a strain analysis method. We found that the materials parameters of InAs required to calculate the strain from the shift in the optical phonon energy of the epilayer were not accurately known. Quantitative strain determination by Raman spectroscopy depends on accurate values of the phonon deformation potentials of InAs and other III–V compounds of interest. Also, DCD is capable of determining much smaller strains than Raman spectroscopy.