Effect of strain and associated piezoelectric fields in InGaN/GaN quantum wells probed by resonant Raman scattering

The influence of pseudomorphic strain and resulting piezoelectric fields on ${\mathrm{In}}_{\mathrm{0.13}}{\mathrm{Ga}}_{\mathrm{0.87}}\mathrm{N/GaN}$ quantum wells has been studied by resonant Raman scattering. The $A_1(\mathrm{LO})$ phonon of ${\mathrm{In}}_{\mathrm{0.13}}{\mathrm{Ga}}_{\mathrm{0.87}}\mathrm{N}$ pseudomorphically strained to GaN is found to be downshifted in frequency by only 3 cm⁻¹ with respect to GaN, which gives evidence for a near cancellation between the much larger frequency downshift of 10 cm⁻¹ reported for unstrained ${\mathrm{In}}_{\mathrm{0.13}}{\mathrm{Ga}}_{\mathrm{0.87}}\mathrm{N}$ and a high-frequency shift of the $A_1(\mathrm{LO})$ phonon induced by the in-plane compressive strain. For excitation in resonance with the fundamental interband transition of the InGaN well, the intensity of first- and second-order scattering by the InGaN $A_1(\mathrm{LO})$ phonon was found to decrease with decreasing excitation power density, and thus increasing strength of the piezoelectric field. This finding is explained by a quenching of the excitonic enhancement in the resonance profile by the piezoelectric field.