. Notechnologies-de-lyon, Les modes d'observations utilisés ont été en champ clair et en champ sombre « Weak Beam G-3G ». Ce dernier mode d'analyse permet d'obtenir une bonne résolution pour l

. La-figure-7, 1 compare les deux modes d'observation sur deux types de dislocation Nous remarquons ainsi que les images présentent une meilleure résolution en champ sombre. Il est toujours difficile de mesurer la taille des dislocations, aussi bien en longueur qu'en largeur . En longueur, car les conditions de préparation ne permettent pas forcément d'avoir un plan d'observation dans la même direction que la dislocation, et en largeur parce que les conditions d'observation font

. Gan, Elles traversent l'ensemble de la couche de GaN avec une direction normale au plan (0001) GaN . Ce type de défaut a été attribué dans la littérature à des dislocations « vis» ou dislocations de type « c

S. Strite, H. Lin, and . Morko¯-e, Progress and prospects for GaN and the III???V nitride semiconductors, Thin Solid Films, vol.231, issue.1-2, pp.197-210, 1993.
DOI : 10.1016/0040-6090(93)90713-Y

M. Leszczynski, H. Teisseyre, T. Suski, I. Grzegory, M. Bockowski et al., Lattice parameters of gallium nitride, Applied Physics Letters, vol.69, issue.1, p.73, 1996.
DOI : 10.1063/1.118123

W. C. Johnson, J. B. Parson, and M. C. Crew, Nitrogen Compounds of Gallium. III, The Journal of Physical Chemistry, vol.36, issue.10, pp.2651-2654, 1932.
DOI : 10.1021/j150340a015

U. Ozgur, D. Hofstetter, and H. Morkoç, Zno devices and applications : a review of current status and future prospects, Proceedings of the IEEE, pp.1255-1268, 2010.

A. Philippe, Caractérisation électrique et optique du nitrure de gallium hexagonal et cubique en vue de l'obtention d'émetteurs bleus, 1999.

M. Levinshtein and M. Shur, Handbook series on semiconductor parameters, World Scientific, issue.2, 1995.

F. Bernardini, V. Fiorentini, and D. Vanderbilt, Spontaneous polarization and piezoelectric constants of III-V nitrides, Physical Review B, vol.56, issue.16, pp.10024-10027, 1997.
DOI : 10.1103/PhysRevB.56.R10024

R. Resta, Macroscopic polarization in crystalline dielectrics: the geometric phase approach, Reviews of Modern Physics, vol.66, issue.3, p.899, 1994.
DOI : 10.1103/RevModPhys.66.899

Y. Liu, T. Egawa, and H. Jiang, Enhancement-mode quaternary AlInGaN/GaN HEMT with non-recessed-gate on sapphire substrate, Electronics Letters, vol.42, issue.15, pp.42884-886, 2006.
DOI : 10.1049/el:20061150

G. Chen, M. Smith, . Lin, S. H. Jiang, M. A. Wei et al., Fundamental optical transitions in GaN, Applied Physics Letters, vol.68, issue.20, p.2784, 1996.
DOI : 10.1063/1.116606

J. Menniger, U. Jahn, O. Brandt, H. Yang, and K. Ploog, Identification of optical transitions in cubic and hexagonal GaN by spatially resolved cathodoluminescence, Physical Review B, vol.53, issue.4, pp.1881-1885, 1996.
DOI : 10.1103/PhysRevB.53.1881

S. Pugh, S. Dj-dugdale, R. Brand, and . Abram, Electronic structure calculations on nitride semiconductors, Semiconductor Science and Technology, vol.14, issue.1, pp.23-31, 1999.
DOI : 10.1088/0268-1242/14/1/003

D. Caughey and R. Thomas, Carrier mobilities in silicon empirically related to doping and field, Proceedings of the IEEE, pp.2192-2193, 1967.
DOI : 10.1109/PROC.1967.6123

T. Mnatsakanov, L. Pomortseva, and S. Yurkov, Semiempirical model of carrier mobility in silicon carbide for analyzing its dependence on temperature and doping level, Semiconductors, vol.35, issue.4, pp.394-397, 2001.
DOI : 10.1134/1.1365181

F. Schwierz, An electron mobility model for wurtzite GaN, Solid-State Electronics, vol.49, issue.6, pp.889-895, 2005.
DOI : 10.1016/j.sse.2005.03.006

T. T. Mnatsakanov, M. E. Levinshtein, L. I. Pomortseva, S. N. Yurkov, G. S. Simin et al., Carrier mobility model for GaN, Solid-State Electronics, vol.47, issue.1, pp.111-115, 2003.
DOI : 10.1016/S0038-1101(02)00256-3

J. Kim, H. Frenkel, R. Liu, and . Park, Growth by molecular beam epitaxy and electrical characterization of Si???doped zinc blende GaN films deposited on ?????SiC coated (001) Si substrates, Applied Physics Letters, vol.65, issue.1, p.91, 1994.
DOI : 10.1063/1.113085

H. Okumura, K. Ohta, G. Feuillet, K. Balakrishnan, S. Chichibu et al., Growth and characterization of cubic GaN, Journal of Crystal Growth, vol.178, issue.1-2, pp.113-133, 1997.
DOI : 10.1016/S0022-0248(97)00084-5

K. Lischka, Epitaxial ZnSe and cubic GaN : wide-band-gap semiconductors with similar properties ? physica status solidi (b), pp.673-681, 1997.

N. D. Arora, J. R. Hauser, and D. J. Roulston, Electron and hole mobilities in silicon as a function of concentration and temperature, IEEE Transactions on Electron Devices, vol.29, issue.2, pp.292-295, 1982.
DOI : 10.1109/T-ED.1982.20698

E. Alekseev and D. Pavlidis, Microwave potential of GaN-based Gunn devices, Electronics Letters, vol.36, issue.2, pp.176-178, 2000.
DOI : 10.1049/el:20000200

M. Farahmand, C. Garetto, E. Bellotti, K. F. Brennan, M. Goano et al., Monte Carlo simulation of electron transport in the III-nitride wurtzite phase materials system: binaries and ternaries, IEEE Transactions on Electron Devices, vol.48, issue.3, pp.48535-542, 2001.
DOI : 10.1109/16.906448

H. Maruska and J. Tietjen, THE PREPARATION AND PROPERTIES OF VAPOR???DEPOSITED SINGLE???CRYSTAL???LINE GaN, Applied Physics Letters, vol.15, issue.10, p.327, 1969.
DOI : 10.1063/1.1652845

M. Leszczynski, T. Suski, H. Teisseyre, P. Perlin, I. Grzegory et al., Thermal expansion of gallium nitride, Journal of Applied Physics, vol.76, issue.8, p.4909, 1994.
DOI : 10.1063/1.357273

H. Morkoc, Handbook of Nitride Semiconductors and Devices, Materials Properties, Physics and Growth, 2008.

A. Polian, M. Grimsditch, and I. Grzegory, Elastic constants of gallium nitride, Journal of Applied Physics, vol.79, issue.6, pp.3343-3344, 1996.
DOI : 10.1063/1.361236

R. Madar, G. Jacob, J. Hallais, and R. Fruchart, High pressure solution growth of GaN, Journal of Crystal Growth, vol.31, pp.197-203, 1975.
DOI : 10.1016/0022-0248(75)90131-1

F. Mr-ranade, A. Tessier, . Navrotsky, . Leppert, . Sh-risbud et al., Enthalpy of Formation of Gallium Nitride, The Journal of Physical Chemistry B, vol.104, issue.17, pp.4060-4063, 2000.
DOI : 10.1021/jp993752s

H. Hahn and R. Juza, Untersuchungen ??ber die Nitride von Cadmium, Gallium, Indium und Germanium. Metallamide und Metallnitride. VIII. Mitteilung, Zeitschrift f??r anorganische und allgemeine Chemie, vol.244, issue.2, pp.111-124, 1940.
DOI : 10.1002/zaac.19402440203

A. Pisch and R. Schmid-fetzer, In situ decomposition study of GaN thin films, Journal of Crystal Growth, vol.187, issue.3-4, pp.329-332, 1998.
DOI : 10.1016/S0022-0248(98)00006-2

M. Furtado and G. Jacob, Study on the influence of annealing effects in GaN VPE, Journal of Crystal Growth, vol.64, issue.2, pp.257-267, 1983.
DOI : 10.1016/0022-0248(83)90132-X

A. Davydov, . Boettinger, T. Kattner, and . Anderson, Thermodynamic Assessment of the Gallium-Nitrogen System, physica status solidi (a), vol.3, issue.1, pp.407-410, 2001.
DOI : 10.1002/1521-396X(200111)188:1<407::AID-PSSA407>3.0.CO;2-P

D. Maier, M. Alomari, N. Grandjean, J. F. Carlin, M. A. Diforte-poisson et al., Testing the Temperature Limits of GaN-Based HEMT Devices, IEEE Transactions on Device and Materials Reliability, vol.10, issue.4, pp.1-1, 2010.
DOI : 10.1109/TDMR.2010.2072507
URL : https://hal.archives-ouvertes.fr/hal-00579038

D. Maier, M. Alomari, E. Kohn, M. A. Diforte-poisson, C. Dua et al., High temperature stability of nitride-based power hemts, pp.1-4, 2010.

D. Zanato, S. Gokden, N. Balkan, W. Ridley, and . Schaff, The effect of interface-roughness and dislocation scattering on low temperature mobility of 2D electron gas in GaN/AlGaN, Semiconductor Science and Technology, vol.19, issue.3, p.427, 2004.
DOI : 10.1088/0268-1242/19/3/024

J. Webb, H. Tang, S. Rolfe, and J. Bardwell, Semi-insulating C-doped GaN and high-mobility AlGaN/GaN heterostructures grown by ammonia molecular beam epitaxy, Applied Physics Letters, vol.75, issue.7, p.953, 1999.
DOI : 10.1063/1.124252

M. A. Khan, J. W. Yang, G. Simin, R. Gaska, M. S. Shur et al., Piezoelectric doping in AlInGaN/GaN heterostructures, Applied Physics Letters, vol.75, issue.18, pp.752806-2808, 1999.
DOI : 10.1063/1.125156

C. B. Soh, S. J. Chua, S. Tripathy, S. Y. Chow, D. Z. Chi et al., Influence of composition pulling effect on the two-dimensional electron gas formed at al[sub y]in[sub x]ga[sub 1 -x -y]n/gan interface, Journal of Applied Physics, issue.10, p.98103704, 2005.

N. Yokoyama, T. Mimura, M. Fukuta, and H. Ishikawa, A self-aligned source/drain planar device for ultrahigh-speed gaas mesfet vlsis, pp.218-219, 1981.

J. H. Lee, H. S. Yoon, C. S. Park, and H. M. Park, Ultra low noise characteristics of algaas/ingaas/gaas pseudomorphic hemt's with wide head t-shaped gate. Electron Device Letters, pp.16271-273, 1995.

E. Johnson, Physical limitations on frequency and power parameters of transistors, IRE International Convention Record, pp.27-34, 1965.
DOI : 10.1109/IRECON.1965.1147520

R. Keyes, Figure of merit for semiconductors for high-speed switches, Proceedings of the IEEE, pp.225-225, 1972.
DOI : 10.1109/PROC.1972.8593

B. J. Baliga, Power semiconductor device figure of merit for high-frequency applications . Electron Device Letters, IEEE, vol.10, issue.10, pp.455-457, 1989.

W. Schottky, Zur halbleitertheorie der sperrschicht-und spitzengleichrichter. Zeitschrift für Physik A Hadrons and Nuclei, pp.367-414, 1939.
DOI : 10.1007/bf01340116

N. Mott, The Theory of Crystal Rectifiers, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, vol.171, issue.944, p.27, 1939.
DOI : 10.1098/rspa.1939.0051

J. H. Werner and H. H. Guttler, Barrier inhomogeneities at Schottky contacts, Journal of Applied Physics, vol.69, issue.3, pp.1522-1533, 1991.
DOI : 10.1063/1.347243

J. H. Werner and H. H. Guttler, Temperature dependence of Schottky barrier heights on silicon, Journal of Applied Physics, vol.73, issue.3, pp.1315-1319, 1993.
DOI : 10.1063/1.353249

R. Tung, Electron transport at metal-semiconductor interfaces: General theory, Physical Review B, vol.45, issue.23, p.13509, 1992.
DOI : 10.1103/PhysRevB.45.13509

J. Sullivan, . Tung, W. Pinto, and . Graham, Electron transport of inhomogeneous Schottky barriers: A numerical study, Journal of Applied Physics, vol.70, issue.12, pp.7403-7424, 1991.
DOI : 10.1063/1.349737

R. Tung, Electron transport of inhomogeneous Schottky barriers, Applied Physics Letters, vol.58, issue.24, pp.2821-2823, 1991.
DOI : 10.1063/1.104747

R. T. Tung, Recent advances in Schottky barrier concepts, Materials Science and Engineering: R: Reports, vol.35, issue.1-3, pp.1-138, 2001.
DOI : 10.1016/S0927-796X(01)00037-7

J. Bardeen, Surface States and Rectification at a Metal Semi-Conductor Contact, Physical Review, vol.71, issue.10, p.717, 1947.
DOI : 10.1103/PhysRev.71.717

A. M. Cowley and S. M. Sze, Surface States and Barrier Height of Metal???Semiconductor Systems, Journal of Applied Physics, vol.36, issue.10, pp.3212-3220, 1965.
DOI : 10.1063/1.1702952

E. Redondo, N. Blanco, I. Mártil, and G. Gonzalez-díaz, Low interface trap density in rapid thermally annealed al/sin[sub x] :h/inp metal?insulator?semiconductor devices, Applied Physics Letters, issue.7, pp.74991-993, 1999.

A. Ahaitouf, E. Losson, and A. Bath, On the determination of interface state density in n-InP Schottky structures by current???voltage measurements, Solid-State Electronics, vol.44, issue.3, pp.515-520, 2000.
DOI : 10.1016/S0038-1101(99)00269-5

J. Palmour, R. La-lipkin, D. Singh, . Slater, C. Suvorov et al., SiC device technology: remaining issues, Diamond and Related Materials, vol.6, issue.10, pp.1400-1404, 1997.
DOI : 10.1016/S0925-9635(97)00118-0

P. Landsberg, Image Force in Rectifiers, Nature, vol.164, issue.4179, pp.967-968, 1949.
DOI : 10.1038/164967a0

F. Padovani and R. Stratton, Field and thermionic-field emission in Schottky barriers, Solid-State Electronics, vol.9, issue.7, pp.695-707, 1966.
DOI : 10.1016/0038-1101(66)90097-9

Q. Liu and S. Lau, A review of the metal???GaN contact technology, Solid-State Electronics, vol.42, issue.5, p.677, 1998.
DOI : 10.1016/S0038-1101(98)00099-9

J. Guo, F. Feng, and . Pan, Study of Schottky barriers on n-type GaN grown by LP-MOCVD. Solid-State and Integrated Circuit Technology, 4th International Conference on, pp.515-517, 1995.

J. Foresi and T. Moustakas, Metal contacts to gallium nitride, Applied Physics Letters, vol.62, issue.22, p.2859, 1993.
DOI : 10.1063/1.109207

B. Luther, . Mohney, M. A. Tn-jackson, Q. Khan, J. Chen et al., -type GaN, Applied Physics Letters, vol.70, issue.1, p.57, 1997.
DOI : 10.1063/1.119305
URL : https://hal.archives-ouvertes.fr/jpa-00214070

L. Smith, . Davis, . Kim, Y. Carpenter, and . Huang, Microstructure, electrical properties, and thermal stability of Al ohmic contacts to n-GaN, Journal of Materials Research, vol.13, issue.09, p.2257, 1996.
DOI : 10.1103/PhysRevB.17.5044

M. Lin, Z. Ma, . Huang, . Zf-fan, H. Allen et al., Low resistance ohmic contacts on wide band???gap GaN, Applied Physics Letters, vol.64, issue.8, pp.1003-1005, 1994.
DOI : 10.1063/1.111961

W. David, J. D. Jenkins, and . Dow, Electronic structures and doping of InN, x Ga 1?x N, and In x Al 1?x N, pp.3317-3329, 1989.

S. Ruvimov, Z. Liliental-weber, J. Washburn, . Duxstad, Z. F. Haller et al., ???GaN, Applied Physics Letters, vol.69, issue.11, p.1556, 1996.
DOI : 10.1063/1.117060

B. Luther, . Delucca, . Mohney, and . Jr, Analysis of a thin AlN interfacial layer in Ti/Al and Pd/Al ohmic contacts to n-type GaN, Applied Physics Letters, vol.71, issue.26, p.3859, 1997.
DOI : 10.1063/1.120526

J. S. Kwak, J. Y. Se-mohney, R. Lin, and . Kern, Low resistance Al/Ti/n-GaN ohmic contacts with improved surface morphology and thermal stability, Semiconductor Science and Technology, vol.15, issue.7, pp.756-760, 2000.
DOI : 10.1088/0268-1242/15/7/316

J. L. Murray, Phase diagrams of binary titanium alloys, p.354, 1987.

S. Ruvimov, Z. Liliental-weber, J. Washburn, D. Qiao, P. K. Lau et al., Microstructure of Ti/Al ohmic contacts for n-AlGaN, Applied Physics Letters, vol.73, issue.18, p.2582, 1998.
DOI : 10.1063/1.122512

Z. Chen, C. Zx-qin, . Hu, . Hu, Y. Yu et al., Ohmic contact formation of Ti/Al/Ni/Au to n-GaN by two-step annealing method, Materials Science and Engineering: B, vol.111, issue.1, pp.36-39, 2004.
DOI : 10.1016/j.mseb.2004.03.014

Z. Fan, S. N. Mohammad, W. Kim, O. Aktas, A. E. Botchkarev et al., ???GaN, Applied Physics Letters, vol.68, issue.12, p.1672, 1996.
DOI : 10.1063/1.115901

F. Lucolano, F. Roccaforte, A. Alberti, C. Bongiorno, S. D. Franco et al., Temperature dependence of the specific resistance in Ti???Al???Ni???Au contacts on n-type GaN, Journal of Applied Physics, vol.100, issue.12, p.123706, 2006.
DOI : 10.1063/1.2400825

A. Motayed, R. Bathe, M. C. Wood, O. S. Diouf, S. N. Vispute et al., Electrical, thermal, and microstructural characteristics of Ti/Al/Ti/Au multilayer Ohmic contacts to n-type GaN, Journal of Applied Physics, vol.93, issue.2, p.1087, 2002.
DOI : 10.1063/1.1528294

A. Motayed, . Davydov, D. Wj-boettinger, . Josell, I. Shapiro et al., Realization of improved metallization-Ti, Au ohmic contacts to n-GaN for high temperature application. physica status solidi (c), 2005.

H. Lee, G. Bae, and . Yeom, Thermally Stable Ti/Al/W/Au Multilayer Ohmic Contacts on n-Type GaN, Journal of the Korean Physical Society, vol.51, issue.3, p.1046, 2007.
DOI : 10.3938/jkps.51.1046

S. Fernández, R. Peña, M. Rodrigo, . Verdú, M. Sánchez et al., Performance enhancement of ohmic contact on n-GaN using Ti???W as metal barrier, Materials Science and Engineering: B, vol.143, issue.1-3, pp.1-355, 2007.
DOI : 10.1016/j.mseb.2007.07.004

S. Fernández, R. Peña, J. Mt-rodrigo, M. Plaza, . Verdú et al., Low resistance Ti???Al???Ti???W???Au Ohmic contact to n-GaN for high temperature applications, Applied Physics Letters, vol.90, issue.8, p.83504, 2007.
DOI : 10.1063/1.2539670

L. Wang, F. M. Mohammed, and I. Adesida, Characterization of Au and Al segregation layer in post-annealed thin Ti???Al???Mo???Au Ohmic contacts to n???GaN, Journal of Applied Physics, vol.98, issue.10, p.106105, 2005.
DOI : 10.1063/1.2132089

L. Wang, F. M. Mohammed, and I. Adesida, Differences in the reaction kinetics and contact formation mechanisms of annealed Ti???Al???Mo???Au Ohmic contacts on n-GaN and AlGaN???GaN epilayers, Ohmic contacts on n-GaN and AlGaN/ GaN epilayers, p.13702, 2007.
DOI : 10.1063/1.2402791

V. Reddy, S. H. Kim, and T. Y. Seong, Electrical and structural properties of low-resistance Ti/Al/Re/Au ohmic contacts to n-type GaN, Journal of Electronic Materials, vol.77, issue.5, pp.395-399, 2004.
DOI : 10.1007/s11664-004-0190-y

C. T. Lee and H. W. Kao, -type GaN, Applied Physics Letters, vol.76, issue.17, p.2364, 2000.
DOI : 10.1063/1.126347
URL : https://hal.archives-ouvertes.fr/hal-00857436

L. Voss, L. Stafford, R. Khanna, C. Gila, . Abernathy et al., Thermal Stability of Nitride-Based Diffusion Barriers for Ohmic Contacts to n-GaN, Journal of Electronic Materials, vol.57, issue.309, pp.1662-1668, 2007.
DOI : 10.1007/s11664-007-0277-3

H. P. Maruska and J. J. Tietjen, THE PREPARATION AND PROPERTIES OF VAPOR???DEPOSITED SINGLE???CRYSTAL???LINE GaN, Applied Physics Letters, vol.15, issue.10, pp.327-329, 1969.
DOI : 10.1063/1.1652845

P. Perlin, T. Suski, H. Teisseyre, M. Leszczynski, I. Grzegory et al., Towards the Identification of the Dominant Donor in GaN, Physical Review Letters, vol.75, issue.2, pp.296-299, 1995.
DOI : 10.1103/PhysRevLett.75.296

C. Wetzel, W. Walukiewicz, E. E. Haller, J. Ager, I. Grzegory et al., -type gallium nitride under large hydrostatic pressure, Physical Review B, vol.53, issue.3, pp.1322-1326, 1996.
DOI : 10.1103/PhysRevB.53.1322
URL : https://hal.archives-ouvertes.fr/tel-00557992

J. Neugebauer and C. G. Van-de-walle, Gallium vacancies and the yellow luminescence in GaN, Applied Physics Letters, vol.69, issue.4, pp.503-505, 1996.
DOI : 10.1063/1.117767

J. Neugebauer and C. G. Van-de-walle, Atomic geometry and electronic structure of native defects in GaN, Physical Review B, vol.50, issue.11, pp.8067-8070, 1994.
DOI : 10.1103/PhysRevB.50.8067

C. G. Van-de-walle and J. Neugebauer, First-principles calculations for defects and impurities: Applications to III-nitrides, Journal of Applied Physics, vol.95, issue.8, pp.953851-3879, 2004.
DOI : 10.1063/1.1682673

C. Wetzel, T. Suski, J. W. Ager, I. , E. R. Weber et al., Pressure Induced Deep Gap State of Oxygen in GaN, Physical Review Letters, vol.78, issue.20, pp.783923-3926, 1997.
DOI : 10.1103/PhysRevLett.78.3923

M. G. Ganchenkova and R. M. Nieminen, Nitrogen Vacancies as Major Point Defects in Gallium Nitride, Physical Review Letters, vol.96, issue.19, p.196402, 2006.
DOI : 10.1103/PhysRevLett.96.196402

S. Mohney, . Luther, . Wolter, . Tn-jackson, R. Jr et al., TiN and ZrN based ohmic contacts to n-GaN, 1998 Fourth International High Temperature Electronics Conference. HITEC (Cat. No.98EX145), pp.134-137, 1998.
DOI : 10.1109/HITEC.1998.676774

Q. Liu and S. Lau, A review of the metal???GaN contact technology, Solid-State Electronics, vol.42, issue.5, pp.677-691, 1998.
DOI : 10.1016/S0038-1101(98)00099-9

P. Hacke, T. Detchprohm, K. Hiramatsu, and N. Sawaki, ???type GaN grown by hydride vapor phase epitaxy, Applied Physics Letters, vol.63, issue.19, pp.2676-2678, 1993.
DOI : 10.1063/1.110417

B. Akkal, Z. Benamara, H. Abid, A. Talbi, and B. Gruzza, Electrical characterization of Au/n-GaN Schottky diodes, Materials Chemistry and Physics, vol.85, issue.1, pp.27-31, 2004.
DOI : 10.1016/j.matchemphys.2003.11.007
URL : https://hal.archives-ouvertes.fr/hal-00272575

Y. Koyama, T. Hashizume, and H. Hasegawa, Formation processes and properties of Schottky and ohmic contacts on n-type GaN for field effect transistor applications, Solid-State Electronics, vol.43, issue.8, pp.431483-1488, 1999.
DOI : 10.1016/S0038-1101(99)00093-3

E. Kalinina, A. Kuznetsov, . Babanin, A. Va-dmitriev, and . Shchukarev, Structural and electrical properties of Schottky barriers on n-GaN, Diamond and Related Materials, vol.6, issue.10, pp.1528-1531, 1997.
DOI : 10.1016/S0925-9635(97)00115-5

A. C. Schmitz, A. T. Ping, M. A. Khan, Q. Chen, J. W. Yang et al., Metal contacts to n-type GaN, Journal of Electronic Materials, vol.36, issue.4, pp.255-260, 1998.
DOI : 10.1007/s11664-998-0396-5

T. U. Kampen and W. , Barrier heights of GaN Schottky contacts, Applied Surface Science, vol.117, issue.118, pp.388-393, 1997.
DOI : 10.1016/S0169-4332(97)80112-2

Q. Liu, F. Yu, . Deng, J. Lau, and . Redwing, Ni and Ni silicide Schottky contacts on n-GaN, Journal of Applied Physics, vol.84, issue.2, p.881, 1998.
DOI : 10.1063/1.368151

L. Wang, M. I. Nathan, T. Lim, M. A. Khan, and Q. Chen, High barrier height GaN Schottky diodes: Pt/GaN and Pd/GaN, Applied Physics Letters, vol.68, issue.9, pp.1267-1269, 1996.
DOI : 10.1063/1.115948

J. D. Guo, M. S. Feng, R. J. Guo, F. M. Pan, and C. Y. Chang, ???type GaN grown by low???pressure metalorganic chemical vapor deposition, Applied Physics Letters, vol.67, issue.18, pp.672657-2659, 1995.
DOI : 10.1063/1.114327

Q. Z. Liu, L. S. Yu, S. S. Lau, J. M. Redwing, N. R. Perkins et al., Thermally stable PtSi Schottky contact on n-GaN, Applied Physics Letters, vol.70, issue.10, pp.701275-1277, 1997.
DOI : 10.1063/1.118551

G. Chen, . Chang, J. Kc-shen, . Ou, . Chen et al., -GaN Schottky contacts, Applied Physics Letters, vol.80, issue.4, p.595, 2002.
DOI : 10.1063/1.1425455
URL : https://hal.archives-ouvertes.fr/hal-00109057

H. Okamoto and T. Massalski, Thermodynamic assessment of the gold-based binary systems. Noble Metal Alloys : Phase Diagrams, Alloy Phase Stability, Thermodynamic Aspects, Properties and Special Features, pp.265-288, 1985.

N. Miura, T. Nanjo, M. Suita, T. Oishi, Y. Abe et al., Thermal annealing effects on Ni/Au based Schottky contacts on n-GaN and AlGaN/GaN with insertion of high work function metal, Solid-State Electronics, vol.48, issue.5, pp.48689-695, 2004.
DOI : 10.1016/j.sse.2003.07.006

F. Iucolano, F. Roccaforte, F. Giannazzo, and V. Raineri, Influence of high-temperature GaN annealed surface on the electrical properties of Ni/GaN Schottky contacts, Journal of Applied Physics, vol.104, issue.9, p.93706, 2008.
DOI : 10.1063/1.3006133

H. Venugopalan, . Se-mohney, . Luther, . Delucca, . Wolter et al., Phase Formation and Morphology in Nickel and Nickel/Gold Contacts to Gallium Nitride, MRS Proceedings, vol.449, 1997.
DOI : 10.1016/0022-5088(79)90205-4

J. Guo, . Fm-pan, . Feng, . Guo, C. Chou et al., ???type GaN, Journal of Applied Physics, vol.80, issue.3, p.1623, 1996.
DOI : 10.1063/1.363822

A. Motayed, A. V. Davydov, L. A. Bendersky, M. C. Wood, M. A. Derenge et al., High-transparency Ni/Au bilayer contacts to n-type GaN, Journal of Applied Physics, vol.92, issue.9, pp.925218-5227, 2002.
DOI : 10.1063/1.1509109

J. K. Kim, J. H. Je, J. L. Lee, Y. J. Park, and B. T. Lee, Microstructural investigation of Ni/Au ohmic contact on p-type GaN, Journal of the Electrochemical Society, issue.12, pp.1474645-4651, 2000.

L. Dobos, B. Pécz, L. Tóth, Z. J. Horváth, B. Horváth et al., Structural and electrical properties of Au and Ti/Au contacts to n-type GaN, Vacuum, vol.82, issue.8, pp.82794-798, 2008.
DOI : 10.1016/j.vacuum.2007.11.005
URL : https://hal.archives-ouvertes.fr/hal-00356985

D. Defives, Etude du contact Schottky Métal/SiC Application aux redresseurs Schottky de puissance et aux transistors MESFET hyperfréquence, 2000.

J. Kim, F. Ren, A. G. Baca, and S. J. Pearton, Thermal stability of WSix and W Schottky contacts on n-GaN, Applied Physics Letters, vol.82, issue.19, pp.3263-3265, 2003.
DOI : 10.1063/1.1576506

J. K. Sheu, M. L. Lee, W. C. Lai, H. C. Tseng, and G. C. Chi, Rectifying characteristics of WSi 0.8 -GaN Schottky barrier diodes with a GaN cap layer grown at low temperature, Journal of Applied Physics, issue.3, p.98036106, 2005.

J. Hayes, H. Kim, S. Meidia, and . Mahajan, Thermal stability of TaN Schottky contacts on n-GaN, Acta Materialia, vol.51, issue.3, pp.653-663, 2003.
DOI : 10.1016/S1359-6454(02)00444-5

O. Ménard, F. Cayrel, E. Collard, and D. Alquier, Process Parameters Influence on Specific Contact Resistance (SCR) Value for TiAl Ohmic Contacts on GaN Grown on Sapphire, Materials Science Forum, vol.615, issue.617, pp.955-958, 2009.
DOI : 10.4028/www.scientific.net/MSF.615-617.955

J. Ladroue, A. Meritan, M. Boufnichel, P. Lefaucheux, P. Ranson et al., Deep GaN etching by inductively coupled plasma and induced surface defects, Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, vol.28, issue.5, p.1226, 2010.
DOI : 10.1116/1.3478674
URL : https://hal.archives-ouvertes.fr/hal-00519022

E. Rhoderick and R. Williams, Metal-semiconductor contacts, 1988.

E. Rutherford, International Conference on the Structure of Matter, Nature, vol.92, issue.2299, pp.347-347, 1914.
DOI : 10.1038/092347b0

N. Thierry-jebali, O. Menard, R. Chiriac, E. Collard, C. Brylinski et al., Low temperature (down to 450 ? C) annealed TiAl contacts on N-type BIBLIOGRAPHIE gallium nitride characterized by differential scanning calorimetry, physica status solidi

C. Lu, H. Chen, X. Lv, X. Xie, and S. N. Mohammad, -GaN, Journal of Applied Physics, vol.91, issue.11, p.9218, 2002.
DOI : 10.1063/1.1471390
URL : https://hal.archives-ouvertes.fr/hal-00908450

K. Kazmierski and B. De-cremoux, Double Zinc Diffusion Fronts in InP: Correlation with Models of Varying Charge Transfer during Interstitial-Substitutional Interchange, Japanese Journal of Applied Physics, vol.24, issue.Part 1, No. 2, pp.239-242, 1985.
DOI : 10.1143/JJAP.24.239

I. A. Kowalik, B. J. Kowalski, P. Kaczor, B. A. Orlowski, E. Lusakowska et al., Resonant photoemission study of Ti interaction with GaN surface, Surface Science, vol.600, issue.4, pp.873-879, 2006.
DOI : 10.1016/j.susc.2005.12.016

N. Achtziger and W. Witthuhn, -SiC: Identification and characterization by elemental transmutation of radioactive isotopes, Physical Review B, vol.57, issue.19, pp.12181-12196, 1998.
DOI : 10.1103/PhysRevB.57.12181

T. Dalibor, G. Pensl, N. Nordell, and A. Schöner, Electrical properties of the titanium acceptor in silicon carbide, Physical Review B, vol.55, issue.20, pp.13618-13624, 1997.
DOI : 10.1103/PhysRevB.55.13618

J. M. Langer and H. Heinrich, Deep-Level Impurities: A Possible Guide to Prediction of Band-Edge Discontinuities in Semiconductor Heterojunctions, Physical Review Letters, vol.55, issue.13, pp.1414-1417, 1985.
DOI : 10.1103/PhysRevLett.55.1414

J. M. Langer, C. Delerue, M. Lannoo, and H. Heinrich, Transition-metal impurities in semiconductors and heterojunction band lineups, Physical Review B, vol.38, issue.11, pp.7723-7739, 1988.
DOI : 10.1103/PhysRevB.38.7723

H. Hasegawa, Universal alignment of transition metal impurity levels in III???V and II???VI compound semiconductors, Solid State Communications, vol.58, issue.3, pp.157-160, 1986.
DOI : 10.1016/0038-1098(86)90833-1

M. J. Caldas, A. Fazzio, and A. Zunger, A universal trend in the binding energies of deep impurities in semiconductors, Applied Physics Letters, vol.45, issue.6, pp.671-673, 1984.
DOI : 10.1063/1.95351

P. Patsalas and S. Logothetidis, Optical, electronic, and transport properties of nanocrystalline titanium nitride thin films, Journal of Applied Physics, vol.90, issue.9, pp.4725-4734, 2001.
DOI : 10.1063/1.1403677

H. B. Michaelson, The work function of the elements and its periodicity, Journal of Applied Physics, vol.48, issue.11, pp.4729-4733, 1977.
DOI : 10.1063/1.323539

R. C. Glass, L. M. Spellman, and R. F. Davis, Low energy ion???assisted deposition of titanium nitride ohmic contacts on alpha (6H)???silicon carbide, Applied Physics Letters, vol.59, issue.22, pp.592868-2870, 1991.
DOI : 10.1063/1.105836

R. Hackam and P. Harrop, Electrical properties of nickel-low-doped n-type gallium arsenide Schottky-barrier diodes, IEEE Transactions on Electron Devices, vol.19, issue.12, pp.1231-1238, 1972.
DOI : 10.1109/T-ED.1972.17586

S. Hong, T. Yao, . Kim, T. Sy-yoon, and . Kim, Origin of hexagonal-shaped etch pits formed in (0001) GaN films, Applied Physics Letters, vol.77, issue.1, p.82, 2000.
DOI : 10.1063/1.126884

D. Cherns, W. T. Young, and F. A. Ponce, Characterisation of dislocations, nanopipes and inversion domains in GaN by transmission electron microscopy, Materials Science and Engineering: B, vol.50, issue.1-3, pp.1-376, 1997.
DOI : 10.1016/S0921-5107(97)00171-2

E. Valcheva, T. Paskova, and B. Monemar, Nanopipes and their relationship to the growth mode in thick HVPE-GaN layers, Journal of Crystal Growth, vol.255, issue.1-2, pp.19-26, 2003.
DOI : 10.1016/S0022-0248(03)01190-4

J. Weyher, L. Macht, G. Kamler, J. Borysiuk, and I. Grzegory, Characterization of GaN single crystals by defect-selective etching, physica status solidi (c), vol.93, issue.274, pp.821-826, 2003.
DOI : 10.1002/pssc.200306248

J. Weyher, Characterization of wide-band-gap semiconductors (GaN, SiC) by defect-selective etching and complementary methods, Superlattices and Microstructures, vol.40, issue.4-6, pp.4-6279, 2006.
DOI : 10.1016/j.spmi.2006.06.011

E. Jezierska, M. Weyher, J. Rudzinski, and . Borysiuk, TEM observation of nanopipes in heteroepitaxial GaN, The European Physical Journal Applied Physics, vol.27, issue.1-3, pp.255-258, 2004.
DOI : 10.1051/epjap:2004061

W. Qian, M. Gs-rohrer, K. Skowronski, . Doverspike, and . Rowland, Open???core screw dislocations in GaN epilayers observed by scanning force microscopy and high???resolution transmission electron microscopy, Applied Physics Letters, vol.67, issue.16, p.2284, 1995.
DOI : 10.1063/1.115127

J. Elsner, R. Jones, P. K. Sitch, V. D. Porezag, M. Elstner et al., Theory of Threading Edge and Screw Dislocations in GaN, Physical Review Letters, vol.79, issue.19, pp.793672-3675, 1997.
DOI : 10.1103/PhysRevLett.79.3672

T. Hino, S. Tomiya, T. Miyajima, K. Yanashima, S. Hashimoto et al., Characterization of threading dislocations in GaN epitaxial layers, Applied Physics Letters, vol.76, issue.23, p.3421, 2000.
DOI : 10.1063/1.126666

I. Arslan and N. D. Browning, Role of Oxygen at Screw Dislocations in GaN, Physical Review Letters, vol.91, issue.16, p.165501, 2003.
DOI : 10.1103/PhysRevLett.91.165501

M. E. Hawkridge and D. Cherns, Oxygen segregation to dislocations in GaN, Applied Physics Letters, vol.87, issue.22, p.221903, 2005.
DOI : 10.1063/1.2136224

C. Mavroidis, J. J. Harris, M. J. Kappers, N. Sharma, C. J. Humphreys et al., Observation of thermally activated conduction at a GaN???sapphire interface, Applied Physics Letters, vol.79, issue.8, pp.791121-1123, 2001.
DOI : 10.1063/1.1395525

S. J. Pearton, H. Cho, J. R. Laroche, F. Ren, R. G. Wilson et al., Oxygen diffusion into SiO[sub 2]-capped GaN during annealing, Applied Physics Letters, issue.19, pp.752939-2941, 1999.

B. Chung and M. Gershenzon, The influence of oxygen on the electrical and optical properties of GaN crystals grown by metalorganic vapor phase epitaxy, Journal of Applied Physics, vol.72, issue.2, pp.651-659, 1992.
DOI : 10.1063/1.351848

L. T. Romano, C. G. Van-de-walle, J. W. Ager, I. , W. Götz et al., Effect of Si doping on strain, cracking, and microstructure in GaN thin films grown by metalorganic chemical vapor deposition, Journal of Applied Physics, vol.87, issue.11, pp.7745-7752, 2000.
DOI : 10.1063/1.373529

D. D. Koleske, A. E. Wickenden, R. L. Henry, M. E. Twigg, J. C. Culbertson et al., Enhanced GaN decomposition in H2 near atmospheric pressures, Applied Physics Letters, vol.73, issue.14, pp.732018-2020, 1998.
DOI : 10.1063/1.122354

D. D. Koleske, A. E. Wickenden, and R. L. Henry, GaN Decomposition in Ammonia, MRS Proceedings, vol.395, issue.1, pp.3-3, 1999.
DOI : 10.1116/1.590163

H. Suzuki, R. Togashi, H. Murakami, Y. Kumagai, and A. Koukitu, Theoretical investigation on the decomposition process of GaN(0001) surface under a hydrogen atmosphere, Journal of Crystal Growth, vol.311, issue.10, 2009.
DOI : 10.1016/j.jcrysgro.2009.01.096

A. Rebey, T. Boufaden, and B. Jani, In situ optical monitoring of the decomposition of GaN thin films, Journal of Crystal Growth, vol.203, issue.1-2, pp.12-17, 1999.
DOI : 10.1016/S0022-0248(99)00081-0

K. Lorenz, M. Gonsalves, W. Kim, V. Narayanan, and S. Mahajan, Comparative study of GaN and AlN nucleation layers and their role in growth of GaN on sapphire by metalorganic chemical vapor deposition, Applied Physics Letters, vol.77, issue.21, pp.773391-3393, 2000.
DOI : 10.1063/1.1328091

L. Braginsky, V. Shklover, H. Hofmann, and P. Bowen, nanostructures, Physical Review B, vol.70, issue.13, p.134201, 2004.
DOI : 10.1103/PhysRevB.70.134201

D. M. Liu, C. C. Tuan, and . Chiu, Thermal diffusivity, heat capacity and thermal conductivity in Al2O3???Ni composite, Materials Science and Engineering: B, vol.31, issue.3, pp.287-291, 1995.
DOI : 10.1016/0921-5107(94)01163-X

G. A. Slack, Crystals from 3?? to 300??K, Physical Review, vol.126, issue.2, pp.427-441, 1962.
DOI : 10.1103/PhysRev.126.427

D. Kotchetkov, J. Zou, A. A. Balandin, D. I. Florescu, and F. H. Pollak, Effect of dislocations on thermal conductivity of GaN layers, Applied Physics Letters, vol.79, issue.26, pp.794316-4318, 2001.
DOI : 10.1063/1.1427153

D. I. Florescu, V. M. Asnin, F. H. Pollak, A. M. Jones, J. C. Ramer et al., Thermal conductivity of fully and partially coalesced lateral epitaxial overgrown GaN/sapphire (0001) by scanning thermal microscopy, Applied Physics Letters, vol.77, issue.10, pp.771464-1466, 2000.
DOI : 10.1063/1.1308057

W. Liu and A. A. Balandin, Temperature dependence of thermal conductivity of AlxGa1???xN thin films measured by the differential 3?? technique, Applied Physics Letters, vol.85, issue.22, pp.5230-5232, 2004.
DOI : 10.1063/1.1829168