Thermal stability of W and WSix contacts on p-GaN

The annealing temperature (400–1100 °C) and measurement temperature (25–300 °C) dependencies of current–voltage characteristics of W and ${\mathrm{WSi}}_{\mathrm{0.45}}$ contacts on $\mathrm{p-}\mathrm{GaN}$ have been compared to the more common Ni/Au metallization. At 25 °C, slightly rectifying characteristics were obtained for all three types of contact, but at 300 °C specific contact resistances in the ${10}^{\text{−2}}\mathrm{\hspace{0.17em}\Omega \hspace{0.17em}}{\mathrm{cm}}^{\mathrm{2}}$ range were obtained for ${\mathrm{WSi}}_{\mathrm{0.45}}$ and Ni/Au. This is due to an increase in Mg acceptor ionization efficiency (from 10% at 25 °C to 57% at 300 °C) and more efficient thermionic hole emission across the metal-GaN interface. Both ${\mathrm{WSi}}_{\mathrm{0.45}}$ and W contacts retained featureless surface morphology for annealing at >900 °C, whereas Ni/Au showed substantial islanding at ⩽700 °C.