Observation of normally forbidden transition from thefirst to the third conduction subband in GaN/AlGaNquantum wells

摘要

Normally forbidden intersubband transitions (ISBTs) from thefirst to the third subband e1-e3 have been observed in GaN/Al0.56Ga0.44Nquantum wells (QWs). This demonstrates that a strong built-in field due tothe piezoelectric and spontaneous polarization effects exists in thestructure. The polarization field destroys the symmetry of a square welland induces a strong ISBT e1-e3, which is forbidden in flat-bandsymmetrical QWs. We have also investigated the dependence of the ISBTenergy on the number of QW periods. With increasing the number ofQWs from 10 to 30, the ISBT spectra were found red-shift. This result canbe attributed to the piezoelectric field being reduced due to partial strainrelaxation of the QW layers, seen in asymmetric reciprocal space maps inX-ray diffraction spectra.