SHALLOW DONORS IN GAN - THE BINDING-ENERGY AND THE ELECTRON EFFECTIVE-MASS

Fourier transform infrared absorption spectroscopy has been performed on a GaN epitaxial film grown by the hydride vapor phase epitaxy on sapphire substrate. We observe a transition at 215 cm(-1) with a half width of 2 cm(-1), which we attribute to an electronic transition on the basis of temperature dependent measurements. We assign to the 1s-2p transition of the residual shallow donors. Using effective mass theory neglecting anisotropies in the effective mass and dielectric constant the binding energy of the shallow donors is calculated to be (35.5 +/- 0.5) meV. The electron effective mass is (0.236 +/- 0.005) m(0),. Based on this knowledge, the energy separation between the donor-acceptor and the band-acceptor transitions as seen in photoluminescence at 45 K can be used to evaluate the donor concentration in the epitaxial films.