"In-plane anisotropic strain of ZnO microcrystallites grown on tilted (0001) sapphire", F. Siah, Z. Yang, Z. K. Tang, G. K. L. Wong, M. Kawasaki, A. Ohtomo, and H. Koinuma, and Y. Segawa, J. Appl. Phys. 88 (5), 2480 (2000)

We have found that ZnO films consisting of epitaxially ordered arrays of closely packed hexagonal microcrystallites grown on vicinal (1000) sapphire exhibit biaxial in-plane optical anisotropy. The optical anisotropy resonance occurs near the band gap energy of ZnO. The line shape of the resonance is consistent with that induced by an in-plane anisotropic strain. The direction of the anisotropy coincides with the projection of the miscut direction of the (0001) sapphire substrates onto the sample surface plane. The magnitude of the anisotropy is generally larger for films with high crystalline quality, and on substrates with larger miscut angles. A possible origin of the strain anisotropy due to the mis-cut angle and the difference in thermal expansion rate of sapphire along its c and a axes is proposed.

"Optical anisotropy of InAs submonolayer quantum wells in (311) GaAs Matrix", Y. H. Chen, Z. Yang, Z. G. Wang, B. Xu, J. B. Liang, J. J. Qian, Phys. Rev. B 56, 6770 (1997)

The in-plane optical anisotropy which comes from the heavy hole and the light hole transitions in InAs submonolayers inserted in (311)-oriented GaAs matrix is studied by reflectance-difference spectroscopy (RDS). The steplike density of states obtained from RDS demonstrates that the ultrathin InAs layers should be regarded as two-dimensional quantum wells rather than isolated clusters, even for the sample with only 1/3 monolayer InAs. The degree of anisotropy is found to be independent of the layer coverage, and is within the intrinsic anisotropy of (311)-oriented ultrathin quantum wells, indicating that there is little structural or strain anisotropy in the InAs submonolayer grown on (311) GaAs surface.

"Optical anisotropy of (11N) GaAs/GaAlAs superlattices", Z. Yang, Y. H. Chen, Y. Q. Wang, Appl. Surf. Sci. 123/124, 391 (1998)

The in-plane anisotropy of a series of (113), (115), (001) vicinal, and singular (001) oriented GaAs/Ga0.7Al0.3As superlattices (SL's) has been studied by reflectance difference spectroscopy (RDS) in the photon energy range covering both the E0 and the E1 energies of GaAs, and from 80 to 300 K. The polarity and the energy position of the observed RDS resonances near the E0 energy confirm that these resonances are indeed originated from the heavy hole (HH), the light hole (LH), and the G7 LH subbands in the GaAs wells. The transition strength anisotropy is in agreement with the multiband k*p model calculations. Sizable RD resonances have been observed in the (100) singular SL's at low temperatures, which are believed to be due to the HH and the LH exciton bound to anisotropic interface structural defects. The optical anisotropy of the SL's near the E1 critical energy of GaAs shows complicated resonance patterns.