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°C for 10 s. The 750, 950 and 1050°C anneals produced good ohmic contacts with contact resistivities ranging from 2.6·10−6 to 1.1·10−4 Ωcm2, as measured by the transmission line model technique, while the 850°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 ÅW/500 ÅWSi/3500 Å n+-In1−xAlxN/AlN with x=0, 0.27 and 0.46 was deposited on sapphire and RTA treated at temperatures up to 700°C. Contact resistivity values of 1·10−6 to 1·10−5 Ωcm2 were obtained. The contact resistivity increased as the annealing temperature increased.