Low-resistance Ni/Au ohmic contact to Mg-doped of Al0.15Ga0.85N/GaN superlattices

Electrical properties of Ni (6 nm)/Au (14 nm) contacts to Mg-doped strained layer Al0.15Ga0.85N/GaN supel lattices have been analyzed. The hole concen tration and mobility are around 1 x 10(18) cm(3) and 10 cm(2)/V s, respecti vely. Hall effect measurements for this structure show a high conductivity that the high activation efficiency of Mg is due to the strain-induced piez oelectric field. The temperature-dependence resistivity result suggested th at high-hole concentration can enhance tunneling transport for field emissi on and thereby reducing the contact resistance of metal-semiconductor inter face. Before thermal alloying, the current-voltage (I-V characteristic of N i/Au contact on p-type Al0.15Ga0.85N/GaN SLs shows non-ohmic behavior. As t he alloying temperature increases to 600 degreesC, the I-V curve shows a ch aracteristic of ohmic contact. A specific contact resistance as low as 4.0 x 10(-6) Omega cm(2) was obtained at alloying temperature of 650 degreesC f or 5 min in N-2 ambient. (C) 2001 Published by Elsevier Science Ltd.