Unintentionally doped n-type Al0.67Ga0.33N epilayers -: art. no. 261902

Unintentionally doped Al0.67Ga0.33N epilayers were grown on AlN/sapphire templates by metalorganic chemical vapor deposition. Optimized undoped Al0.67Ga0.33N epilayers exhibited an n-type conductivity as confirmed by Hall-effect measurement with a room-temperature resistivity of about 85 Omega cm. Variable temperature Hall-effect measurement revealed the existence of a shallow donor level with activation energy of about 90 meV. The photoluminescence (PL) spectra exhibited an emission peak at 4.13 eV (4.06 eV) related to an impurity transition at 10 K (300 K). Temperature dependent PL measurement also confirmed the existence of a shallow donor with comparable activation energy as that obtained by Hall-effect measurement. Isolated oxygen impurities are believed to be a strong candidate of the donor that remains as a shallow state in AlxGa1-xN up to x similar to 0.7. Compensating defects and the nature of the O donor in Al0.67Ga0.33N epilayers are also discussed.