Optical properties of Si-, Ge- and Sn-doped GaN

Photoluminescence and reflectance spectra of Si-, Ge- and Sn-doped GaN epilayers grown on sapphire substrates at 10 K have been investigated, by which ionization energies on the Ga site were determined as 29, 30 and 33 meV, respectively. To investigate the coherent properties of excitons, the dephasing times of excitons in undoped and Si-doped GaN on sapphire substrates and freestanding GaN were measured using the degenerate four-wave mixing technique. The resulting homogeneous broadenings in undoped and Si-doped GaN on sapphire substrates were about twice as large as that in freestanding GaN, which indicates that defect-induced scattering is stronger in the former than in the latter.