INVESTIGATION OF ALUMINUM OHMIC CONTACTS TO N-TYPE GAN GROWN BY MOLECULAR-BEAM EPITAXY

Using epi-layers of different doping concentrations, we have investiga ted aluminium contacts on n-type gallium nitride grown by plasma sourc e molecular beam epitaxy. To achieve repeatable and reliable results i t was found that the semiconductor needed to be etched in aqua-regia b efore the deposition of the contact metallization. Scanning electron m icrographs of the semiconductor surface show a deterioration of the se miconductor surface on etching. The specific contact resistivity of th e etched samples were, however, superior. Annealing the contacts at 60 0 degrees C produced contacts with the lowest specific contact resista nce of 2.0 x 10(-4) Ohm cm(2). The long-term aging of these contacts w as also investigated. The contacts and the sheet resistance were both found to deteriorate over a three-month period.