| The processing and properties of ohmic contacts to p-Al xGa1-xN were examined in this investigation to advance our understanding of the electrical properties and materials related issues of these contacts.;Several approaches for fabricating ohmic contacts to p-GaN (most of which are based on the late transition metals Ni, Pd, and Pt, or the noble metal Au) have been reported in the literature. In this investigation, the effects of increasing the p-AlxGa 1-xN AlN fraction x from x = 0 to x = 0.4 was examined for two of the most promising approaches for fabricating ohmic contacts to p-GaN---the use of an aggressive boiling aqua regia (3 HCl: 1 HNO3) surface treatment of the p-GaN prior to deposition of a Pd-based contact, or the annealing of thin Ni/Au contacts in an O2-containing ambient to form a NiO/Au contact. Comparison of these contacts to Ni-based contacts that were annealed in N 2 indicate that both of these approaches lose their effectiveness as x is increased from zero. The effects of annealing on the electrical properties of Ni, Pd, Pt, and Au contacts to p-Al0.45 Ga0.55N were also studied. For Pd, Pt, and Au contacts annealed in excess of 700 to 750°C, the contact resistivity dropped significantly, but a rapid increase in contact resistivity was observed following their exposure to light with wavelengths longer than 600 nm. A hypothesis is presented to describe this degradation.;The interfacial reactions between Ni, Pd, or Au and Alx Ga1-xN with x = 0.15 or 0.47 were also examined, with an emphasis on analyzing the distribution of Al and Ga in the vicinity of the Ni/, Pd/, or Au/Al xGa1-xN interfaces following annealing. (Abstract shortened by UMI.). |
