Excitonic and deep-level emission from N- and Al-polar homoepitaxial AlN grown by molecular beam epitaxy

Using low-temperature cathodoluminescence spectroscopy, we study the properties of N- and Al-polar AlN layers grown by molecular beam epitaxy on bulk AlN{0001}. Compared with the bulk AlN substrate, layers of both polarities feature a suppression of deep-level luminescence, a total absence of the prevalent donor with an exciton binding energy of 28 meV, and a much increased intensity of the emission from free excitons. The dominant donor in these layers is characterized by an associated exciton binding energy of 13 meV. The observation of excited exciton states up to the exciton continuum allows us to directly extract the & UGamma;(5) free exciton binding energy of 57 meV.

Automated summary

Using low-temperature cathodoluminescence spectroscopy, the properties of N- and Al- polar AlN layers grown on bulk AlN{0001} by molecular beam epitaxy are studied. Both polarities of layers exhibit a suppression of deep-level luminescence compared to the bulk AlN substrate, a total absence of the prevalent donor with an exciton binding energy of 28 meV, and a much increased intensity of the emission from free excitons. The dominant donor in these layers has an associated exciton binding energy of 13 meV. Additionally, the observation of excited exciton states up to the exciton continuum allows for the direct extraction of the Γ(5) free exciton binding energy of 57 meV.