Quantum confined Stark effect due to built-in internal polarization fieldsin (Al,Ga)N/GaN quantum wells

(Al,Ga)N/GaN quantum wells have been studied by temperature-dependent lumin escence and reflectivity. The samples were grown by molecular beam epitaxy on (0001) sapphire substrates, and well widths were varied from 3 to 15 mon olayers (ML's) with a 2-ML increment, thus providing a reliable data set fo r the study of the well width dependence of transition energies. The latter shows a strong quantum confined Stark effect for wide wells, and an intern al electric-field strength of 450 kV/cm is deduced. X-ray diffraction perfo rmed on the same samples shows that the GaN layers are nearly unstrained, w hereas the (AI,Ga)N barriers are pseudomorphically strained on GaN. We conc lude that the origin of the electric field is predominently due to spontane ous polarization effects rather than a piezoelectric effect in the well mat erial. [S0163-1829(98)50944-7].