Stress-induced optical anisotropies measured by modulated reflectance

Abstract

In the last few years, the understanding of information delivered by reflectance difference/anisotropy spectroscopy (RAS) has grown considerably. However, a full understanding of this optical technique is not yet achieved because surface, interface and bulk effects are present particularly where heteroepitaxial systems are concerned. This is especially true for the case of resonances at the bulk critical points of the dielectric function, which either resemble the dielectric function or its derivative. Previous RAS experiments on zincblende and diamond structure semiconductors found optical anisotropies in the vicinity of the E 0 , E 1 and E 1 + 1 critical points. In this review, the origin of these structures is discussed and it is shown that anisotropic in-plane strain in the epilayer or bulk induces resonances at these critical points. This in-plane strain is either caused by the boundaries of the epilayer system (i.e. the surface or the interface) or by symmetry breaking via a surface electric field or a preferred orientation of dislocations. These findings are best supported by applying additionally photoreflectance difference spectroscopy (PRD), where the difference between a spectrum taken with linearly polarized light and with unpolarized light is measured. In contrast to RAS, PRD spectroscopy is specific to the symmetry breakdown occurring due to band bending via the surface or interface electric field and stress.

Evolution of wetting layer of InAs∕GaAs quantum dots studied by reflectance difference spectroscopy

“…A rapid increase in the RDS signal at 2.5 eV has been observed in situ at the onset of the InGaAs/ GaAs dot formation, which was attributed to the changes in the strain and morphology of the InGaAs layer. 18 In summary, the evolution of the WL with the InAs dot formation and ripening process has been studied by RDS. The transitions between FM, SK and R growth modes can be clearly revealed by the different LH transition energy of the WL.…”

Measurement of the Surface Strain Induced by Reconstructed Surfaces of GaAs (001) Using Photoreflectance and Reflectance-Difference Spectroscopies

“…Nondestructive probes, such as optical ones, are therefore of prime importance to study the complex phenomena associated with such surfaces. Reflectance-difference spectroscopy (RDS) and photoreflectance difference (PR-D) spectroscopy are two complementary techniques that have been used for the characterization of GaAs (001) surfaces [1][2][3][4][5][6][7].…”

Optical anisotropy and magneto-optical properties of Ni on preoxidizedCu(110)

“…24,25 Furthermore, RAS is sensitive to symmetry reducing effects such as, e.g., atomic surface steps 27 and uniaxial stress within the surface plane. 28,29 MOKE at a single photon wavelength, on the other hand, is a well established and powerful tool to investigate the magnetic properties of ferromagnetic layers. 3,12,20,[30][31][32][33][34] MOKE spectroscopy can give useful information on the modification of the electronic structure, 4,35 but has rarely been used so far.…”