Deep electron and hole traps in freestanding n-GaN grown by hydride vapor phase epitaxy

Deep level electron and hole traps were studied by means of deep level transient spectroscopy with electrical and optical injection on a freestanding thick n-GaN sample with low dislocation density. It is shown that at both the upper and the lower surface of the sample there exists a thin, ∼0.5 μm layer of damaged material with lowered concentration of electrons and enhanced density of deep centers. Deep in the bulk of the film the densities of the majority of the electron and hole traps are shown to be very low, but measurably higher on the lower face (N face), which was originally closer to the Al2O3 substrate. The two faces are also shown to similarly differ in the density of deep hole traps whose concentration is deduced from low-temperature capacitance–voltage measurements in the dark and after illumination (such traps were previously associated with dislocation states). The concentration of persistent photocapacitance centers is shown to be very low on both sides and considerably lower than previous...