Effect of oxygen on the crystallinity and defect state of AlxGa1−xN epilayers

The effect of oxygen incorporation on the crystal quality and defect states in AlxGa1−xN epilayers (x = 0.4, 0.6, 0.8) grown by hydride vapor phase epitaxy with and without oxygen gas flow were studied. On the basis of the full width at half-maximum value of the (102) X-ray diffraction rocking curve, the crystal quality of AlxGa1−xN with oxygen was better than that of AlxGa1−xN without oxygen as the Al/Ga ratio increased. In Al0.6Ga0.4N epilayers with and without oxygen, two deep traps of H1ʹ and H2ʹ were measured by deep level transient spectroscopy. All traps were hole-like traps with activation energies of 1.28 eV (H1ʹ) and 0.61 eV (H2ʹ), which are the same as traps H1 and H2 measured in Al0.4Ga0.6N. Al0.8Ga0.2N with oxygen had only the D1 trap, as observed by thermally stimulated current, while the sample without oxygen has two traps of D1 (0.80 eV) and D2 (0.64 eV). The trap densities in AlxGa1−xN epilayers decreased with oxygen as the Al mole fraction increased in AlxGa1−xN. Therefore, the oxygen atoms can improve the crystal quality and suppress the defect states in AlxGa1−xN epilayers.