The reflectance of basal-plane epitaxial layers of GaN has been measured between 5 and 30 eV, and Kramers-Kronig analyzed to get the dielectric function and the electron-energy-loss function. The second derivative of the reflectance with respect to energy was obtained in the region of Ga $3d$→ conduction-band excitations. The latter show weak structure from transitions to $\Gamma$ final states and stronger structures to final states along $U$, both split by the 0.40-eV Ga $3d$ spin-orbit splitting. The loss function exhibits two peaks, the stronger one at 19.0 eV, below the expected 23.3 eV, while the weaker one is at 23.2 eV.

• Received 8 June 1981

DOI:https://doi.org/10.1103/PhysRevB.24.4629