Free and bound exciton fine structures in AlN epilayers grown by low-pressure metalorganic vapor phase epitaxy

Abstract

Exciton fine structures were observed in partially polarized optical reflectance and cathodoluminescence (CL) spectra of AlN epilayers grown by low-pressure metalorganic vapor phase epitaxy on (0001) Al2O3 substrates. A few free and four bound exciton lines were clearly resolved in the low-temperature CL spectra of the lowest threading dislocation density (∼1×108 cm−2) AlN film. From the energy difference between the ground-state and the first excited states, the hydrogenic A-exciton binding energy in the present compressively strained (Δa/a≈−1.68%) AlN was estimated to be approximately 51 meV.