Investigation of the mechanism for Ti/Al ohmic contact on etched n-GaN surfaces

In this study, the mechanism for ohmic contact of Ti/Al bilayer formation o n as-grown, etched and postetch annealed GaN surfaces were investigated. A nonalloyed Ti/Al ohmic contact to etched GaN surface, with postetch anneali ng prior to metal deposition, was obtained. The specific contact resistance of 2.3x10(-4) Omega cm(2) was obtained. The nonalloyed ohmic contact may b e attributed to the postetch annealing which generates nitrogen vacancies t hat result in a heavily n-type surface thereby forming a tunneling junction . On the other hand, the nonalloyed Ti/Al contact on as-grown and as-etched GaN surfaces exhibits non-ohmic behavior. After alloying at 500 degrees C for 5 min, Ti/Al contacts on as-grown, as-etched and postetched annealing G aN surfaces have specific contact resistances around 9.8x10(-5,) 1x10(-4), and 7.2x10(-5) Omega cm(2), respectively. Nonalloyed Ti/Al ohmic contacts w ould be especially useful for fabricating high breakdown, recessed-gate fie ld effect transistors on GaN since the moderate postannealing condition con verts only the near surface layer to heavily n type. (C) 2000 American Vacu um Society. [S0734-211X(00)00902-1].