Electron confinement in strongly coupled GaN∕AlN quantum wells

The electron confinement in double GaN∕AlN quantum wells coupled by an ultrathin AlN barrier has been investigated by means of structural and optical measurements. The intersubband absorption spectra present two peaks attributed to the e1-e2 and e1-e3 transitions, respectively. The results of photoluminescence and intersubband spectroscopies are compared with simulations of the electronic structure based on the envelope function formalism. A good agreement is obtained for all investigated samples. These results provide clear evidence that the potential drop at the GaN∕AlN heterointerfaces is not abrupt, but is spread over one monolayer.