Conductivity and Hall effect of free-standing highly resistive epitaxial GaN:Fe substrates

Free-standing highly resistive Fe-doped GaN layers grown by hydride vapor phase epitaxy were characterized by temperature-dependent conductivity and Hall effect measurements. Samples with a room-temperature resistivity of 1.6×107–6×108Ωcm and a Hall mobility of ∼330cm2V−1s−1 showed simple band conduction with the mobility power x=−1.5 and an activation energy 0.58–0.60eV, which can be attributed to a Fe acceptor. Samples with a lower mobility, ⩽10cm2V−1s−1, exhibited an increase of the mobility with temperature. Here, the conduction seems to be strongly influenced by potential barriers at inhomogeneities, with an activation energy of 0.21eV and a barrier height of 0.14–0.18eV. The activation energy 0.36 and 0.40eV, evaluated from the resistivity measurements, does not correspond to that of the Fe acceptor.