| This dissertation is focused on the development of Ohmic and Schottky contacts to both n- and p-type Gallium Nitride for use in microelectronic and optical devices. The goal is to develop low resistance contacts with greater thermal budgets and superior thermal aging characteristics to those commonly in use today as well as to understand the mechanisms by which these contacts may fail. In addition, p-type Ohmic contacts have been used to fabricate light emitting diodes (LEDs) which display far superior aging properties than those made with conventional Ni/Au contacts.;Ohmic contacts to p-GaN were fabricated using a variety of refractory materials. The materials examined were of three basic types: boride, nitride, and the refractory metal Ir. The boride family includes W2B, W 2B5, CrB2, ZrB2, and TiB2. The nitrides examined were TaN, TiN, and ZrN. Contacts based on these materials were fabricated using either a GaN//Ni/Au/X/Ti/Au, GaN//X/Ti/Au, or GaN//Ni/X/Au scheme, where X is the refractory material. Contact resistances as low as ∼1 x 10-4 O/cm2 were consistently achieved after annealing at temperatures from 500-1000°C for 60 s in N2 using these materials for p-GaN with a carrier concentration of ∼1 x 10 17 cm-3. In addition, high temperature thermal aging was performed on selected schemes as well as on devices in order to attempt to estimate long term performance.;Next, nitride-based Ohmic contacts to n-GaN are examined. The nitride was used to replace the conventional Pt, Ni, or Mo diffusion barrier in Ti/Al based contacts, for a contact scheme of GaN//Ti/Al/X/Ti/Au. These contacts achieve a similar specific contact resistance of ∼1 x 10-4 O/cm -2 for samples with a carrier concentration of 1 x 1017 cm-3 as that achieved with a Ti/Au/Pt/Au contact. The contacts are also examined as a function of aging and are found to display less intermixing of layers than those fabricated with a Ni diffusion barrier.;Schottky contacts to p-GaN were also fabricated using the family of boride based materials with the scheme GaN//X/Pt/Au. These were found to exhibit tunneling transport through the metal-semiconductor junction and barrier heights of >3.5 eV were determined from the fit of the current-voltage (IV) curves. X-ray Photoelectron Spectroscopy was used to determine a true barrier height for these borides on p-GaN of 2.7 eV, close to that expected from the Schottky-Mott model. Capacitance-voltage (CV) measurements confirm the IV barrier height, but reveal a thin interfacial layer likely arising from oxidation or defects at the surface. |
