Unintentionally doped n-type Al0.67Ga0.33N epilayers

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 85Ωcm. Variable temperature Hall-effect measurement revealed the existence of a shallow donor level with activation energy of about 90meV. The photoluminescence (PL) spectra exhibited an emission peak at 4.13eV (4.06eV) related to an impurity transition at 10K (300K). 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∼0.7. Compensating defects and the nature of the O donor in Al0.67Ga0.33N epilayers are also discussed.

[1]  Hongxing Jiang,et al.  Achieving highly conductive AlGaN alloys with high Al contents , 2002 .

[2]  Jerry Bernholc,et al.  Doping properties of C, Si, and Ge impurities in GaN and AlN , 1997 .

[3]  C. Walle,et al.  First-principles calculations for defects and impurities: Applications to III-nitrides , 2004 .

[4]  Risto M. Nieminen,et al.  Point-defect complexes and broadband luminescence in GaN and AlN , 1997 .

[5]  Van de Walle CG,et al.  Atomic geometry and electronic structure of native defects in GaN. , 1994, Physical review. B, Condensed matter.

[6]  Hongxing Jiang,et al.  Optical properties of the nitrogen vacancy in AlN epilayers , 2004 .

[7]  Nancy C. Giles,et al.  Controlled oxygen doping of GaN using plasma assisted molecular-beam epitaxy , 2001 .

[8]  K. B. Nam,et al.  Optical and electrical properties of Al-rich AlGaN alloys , 2001 .

[9]  R. Nieminen,et al.  Ab initio study of oxygen point defects in GaAs, GaN, and AlN. , 1996, Physical review. B, Condensed matter.

[10]  K. H. Kim,et al.  Transport properties of highly conductive n-type Al-rich AlxGa1−xN(x⩾0.7) , 2004 .

[11]  Naoki Kobayashi,et al.  Intentional control of n-type conduction for Si-doped AlN and AlXGa1−XN(0.42⩽x<1) , 2002 .

[12]  S. Denbaars,et al.  Metalorganic chemical vapor deposition of highly conductive Al0.65Ga0.35N films , 2003 .

[13]  M. Pophristic,et al.  High-conductivity n-AlGaN with high Al mole fraction grown by metalorganic vapor phase deposition , 2003 .

[14]  D. Chadi,et al.  Stability of deep donor and acceptor centers in GaN, AlN, and BN , 1997 .

[15]  D. Bimberg,et al.  Thermal Dissociation of Excitons Bounds to Neutral Acceptors in High-Purity GaAs , 1971 .

[16]  K. H. Kim,et al.  Silicon doping dependence of highly conductive n-type Al0.7Ga0.3N , 2004 .

[17]  Michael Kneissl,et al.  Metastability of Oxygen Donors in AlGaN , 1998 .