W and W/WSi/In_(1-x)Al_xN ohmic contacts to n-type GaN

摘要

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 deg C for 10 s. The 750, 950 and 1050 deg C anneals produced good ohmic contacts with contact resistivities ranging from 2.6 centre dot 10~(-6) to 1.1 centre dot 10~(-4) OMEGA cm~2, as measured by the transmission line model technique, while the 850 deg C anneal produced leaky rectifying diodes. In the second approach, a graded In_(1-x)Al_xN epilayer facilitates the proper band alignment needed for an ohmic contact. In order to test the feasibility of this approach a stack of 500 AW/ 500 AWSi/3500 A n~+-In_(1-x)Al_xN/AlN with x=0, 0.27 and 0.46 was deposited on sapphire and RTA treated at temepratures up to 700 deg C. Contact resistivity values of 1 centre dot 10~(-6) to 1 centre dot 10~(-5) OMEGA cm~2 were obtained. The contact resistivity increased as the annealing temperature increased.