Analysis of strain depth variations in an In0.19Ga0.81N layer by Raman spectroscopy

In this paper, we report a detailed Raman study carried out on a 120 run thick In0.19Ga0.81N sample with a well-defined strain variation over depth. The results show a frequency shift of the A(1)(LO) phonon from InGaN, when varying the excitation energy from 3.71 eV to 2.33 eV. Comparing the phonon frequencies observed under 3.00 eV (720 +/- 1 cm(-1)) and 3.71 eV (707 +/- 1 cm(-1)) excitation, the role of resonant effects on the outgoing channel is demonstrated, in the former case, and correlated with a strong luminescence at about 2.7 eV Independent structural and optical characterization confirm that the resonance effects are essential to find a consistent interpretation for the frequency shift observed for the A(1)(LO) phonon. Taking into account the depth location of strained and relaxed regions in the layer, it was possible to ascribe the origin of phonon frequencies to each region. Finally, the phonon frequency shift per unit strain parallel to the growth axis, DeltaOmega/Deltaepsilon(zz) = 1690 +/- 213 cm(-1), was estimated.