Extremely sharp dependence of the exciton oscillator strength on quantum-well width in the GaN/AlxGa1-xN system: The polarization field effect - art.no. 121304

Exciton reflectivity from GaN/AlxGa1-xN quantum wells (QWs) shows broad pea ks that are difficult to analyze within a conventional single-free-exciton model. We have applied a new formalism that allows us to separate numerical ly radiative and inhomogeneous broadenings of an exciton resonance comparin g the Fourier-transformed reflection spectra with calculated time-resolved reflectivities. We have found the exciton oscillator strength to decrease d ramatically with the increase of the QW width in GaN/Al0.07Ga0.93N system. The collapse of the oscillator strength is a manifestation of the polarizat ion field effect, as confirmed by our variational calculation. We find that only excitons in very thin quantum wells have an oscillator strength excee ding that of the exciton in bulk GaN.