Thermal oxidation of single crystalline aluminum nitride

Dry thermal oxidation of low defect density aluminum nitride single crystals was investigated by high resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS). Oxidation at 800 °C produced an amorphous oxide layer. In the AlN near the interface were many dislocations, stacking faults and domain boundaries, molecular nitrogen and oxygen. Oxidation at 1000 °C produced a crystalline, epitaxial oxide layer with several large grains and twin structures. Near the interface, the oxide was single phase α-Al2O3, while near the surface the oxide was a mixture of γ-Al2O3 and α-Al2O3. The AlN crystal structure was nearly defect- and oxygen-free. The epitaxial relationship between Al2O3 and AlN was (0001) AlN // (011¯1¯) Al2O3 and [11¯00] AlN // [011¯1] Al2O3.