Analysis of deep traps in hexagonal molecular beam epitaxy-grown GaN by admittance spectroscopy

Abstract

Nominally undoped GaN layers grown by molecular beam epitaxy (MBE) and having resistivities between 105 and 107 Ω were investigated with temperature- and frequency-dependent admittance spectroscopy. The advantage of these measurement methods is shown in terms of the formation of Schottky contacts on high-resistivity GaN layers. The space-charge region, which is needed for detection of deep defects exists at low frequencies only and, therefore, deep level transient spectroscopy (DLTS) measurements fail for this material. Two deep defect levels were identified in MBE-grown GaN layers. The thermal activation energies are (0.45±0.04) and (0.63±0.04) eV, respectively. These deep traps are well known from DLTS and thermal stimulated conductivity measurements in metalorganic vapor phase epitaxy and hydride vapor phase epitaxy-grown GaN.