W and W/WSi/In1-xAlxN ohmic contacts to n-type GaN

Two approaches are investigated in order to obtain good stable ohmic contacts to u-type GaN. In the first one the ohmic contact is enabled by depositing W on an n(+)-GaN region produced by Si implantation. The contacts were RTA treated at 750, 850, 950, and 1050 degrees C for 10 s. The 750, 950 and 1050 degrees C anneals produced good ohmic contacts with contact resistivities ranging from 2.6.10(-6) to 1.1.10(-4) Ohm cm(2), as measured by the transmission line model technique, while the 850 degrees C anneal produced leaky rectifying diodes. In the second approach, a graded In1-xAlxN epilayer facilitates the proper band alignment needed for an ohmic contact. In order to test the feasibility of this approach a stack of 500 Angstrom W/500 Angstrom WSi/3500 Angstrom n(+) -In1-xAlxN/AlN with x = 0, 0.27 and 0.46 was deposited on sapphire and RTA treated at temperatures up to 700 degrees C. Contact resistivity values of 1.10(-6) to 1.10(-5) Ohm cm(2) were obtained. The contact resistivity increased as the annealing temperature increased. (C) 1999 Elsevier Science S.A. All rights reserved.