Abnormal dependence of contact resistivity on hole concentration in nonalloyed ohmic contacts to p-GaN

The dependence of contact resistivity on hole concentration has been investigated for nonalloyed Pd contacts to p-GaN. The hole concentration was varied by changing the Mg concentration, [Mg], in p-GaN. The p-GaN having the [Mg] of 4.5x10(19) cm(-3) showed the hole concentration of 2.2x10(17) cm(-3), where contact resistivity was measured as 8.9x10(-2) Omega cm(2). When the [Mg] increased to 1.0x10(20) cm(-3), the hole concentration was significantly reduced to 2.0x10(16) cm(-3). Nevertheless, the Pd contacts on the p-GaN displayed contact resistivity as low as 5.5x10(-4) Omega cm(2). The abnormal dependence of contact resistivity on hole concentration may be explained by predominant current flow at the Pd/p-GaN interface through a deep level defect band, rather than the valence band. (C) 2002 American Institute of Physics.