Local stress measurements in laterally oxidized GaAs/AlxGa1−xAs heterostructures by micro-Raman spectroscopy

Abstract

Lattice deformation induced in surface GaAs layers by the selective lateral oxidation of buried AlxGa1−xAs layers was determined from the energy shift of the GaAs phonon line in Raman spectra excited with a focused laser beam. The procedure included a correction for the laser beam induced heating effects. The surface GaAs layer was found under small tensile stress in the oxidized regions of our samples with respect to the unoxidized regions. The deformation is 8×10−4 and is the same, within experimental error, for heterostructures incorporating pure AlAs layers or Al0.98Ga0.02As. Strong differences in Raman efficiency, as well as in photoluminescence efficiency, were observed for different samples, which are discussed in terms of the GaAs/oxide interface nonradiative recombination efficiency.

Strain relaxation of InGaAs by lateral oxidation of AlAs

“…Two groups have used micro-Raman spectroscopy to estimate the strain in GaAs cap layers. 12,13 In the investigation of Landesman et al, micro-Raman spectroscopy was used to measure the deformation of a 1000 Å GaAs cap due to the oxidation of a 1000 Å AlAs layer lying directly beneath the cap. The strain induced in the cap layer was determined to be 0.08%.…”

Strain in wet thermally oxidized square and circular mesas

“…In general, the GaAs LO phonon is observed at a lower wave number in the light regions, as compared to its position in the dark regions. Because of unequal heating in oxidized and unoxidized samples, 11 we cannot make a direct comparison of phonon positions in our samples before and after oxidation. However, we can obtain an estimate of the strain induced in the samples by the oxidation process by assuming an unstrained GaAs LO phonon position of 291.8 cm Ϫ1 .…”

“…[8][9][10] As demonstrated by Landesman et al, the oxidation process induces local strain in the GaAs cap layer at the oxide-AlAs interface. 11 Because of the reduced oxidation rate in the ͓011͔ direction, the volume contraction of the oxide will not be symmetric with respect to the center of the mesa. This effect should be greatest as the oxidation nears completion and may explain the drumhead patterns observed in mesas, which are almost completely oxidized.…”

“…[8][9][10] Because the measurements were taken from the ͑100͒ face, observation of the TO modes is forbidden. 11 Therefore, we are only concerned with the GaAs LO phonon. The frequency of this mode is 291.8 cm Ϫ1 in unstrained GaAs.…”

“…With ϭ⍀ 2 Ϫ ‫ؠ‬ 2 and P i j ϭ ͚ lm i jlm lm , Eq. ͑1͒ becomes Assuming that the strain is uniform in the GaAs cap layer, we expect a biaxial stress 11,14 yy ϭ zz ϭX, xx ϭ xy ϭ yz ϭ zx ϭ0. Under this applied ͑100͒ coplanar stress X, the nonzero components of the strain tensor can be written as 14 ʈ ϭ yy ϭ zz ϭ͑S 11 ϩS 12 ͒X, ͑3͒…”