The thermal stability of nonalloyed ohmic contacts to AlGaN/GaN heterostructures

Degradation of nonalloyed ohmic contacts with heavily doped GaN epitaxially grown to the heterostructures with two-dimensional electron gas has been investigated. The change in the relative contact resistivity at temperatures of up to 600$^\circ$C for the Ti/Pd/Au, Cr/Au, and Cr/Pd/Au metallization compositions has been studied. It is demonstrated that the Cr/Pd/Au metallization composition, the resistivity of which decreases at working temperatures of 400$^\circ$C, is the most resistant to the effect of temperature. It is shown for the first time that the largest contribution to the increase in the contact resistivity to two-dimensional electron gas upon heating above 400°C is made by the resistivity of the Cr/Pd/Au–$n^+$-GaN metal–dielectric structure, while, at temperatures of 400$^\circ$C and higher, the resistance between heavily doped GaN and two-dimensional electron gas decreases.