Temperature-dependent contact resistivity of radio frequency superimposed direct current sputtered indium tin oxide ohmic contact to p-type gallium nitride

The temperature-dependent contact resistivity of radio frequency (RF) superimposed direct current (DC) sputtered indium tin oxide (ITO) contacts to p-type gallium nitride (p-GaN) films as well as the temperature-dependent sheet resistivity of p-GaN films were investigated to understand the carrier transport mechanism of the sputtered ITO ohmic contacts to p-GaN. As the measurement temperature was decreased from 400 to 200 K, the contact resistivity increased by three orders of magnitude. Furthermore, the sheet resistivity of the p-GaN increased linearly with exp (1/Temperature(T))1/4 from 200 to 340 K, indicating variable-range hopping (VRH) conduction via the Mg-related deep level defect (DLD) band. Based on the VRH conduction model, the effective barrier height between the sputtered ITO and the DLD band were calculated to be 0.12 eV, which is sufficiently low to explain the formation of the low contact resistivity of the RF superimposed DC sputtered ITO contacts to p-GaN (~ 10− 2 Ω-cm2).