Terahertz Spectroscopy of Candidate Oxides in MIM Diodes for Terahertz Detection

We report the utilization of terahertz time-domain spectroscopy (THz-TDS) to measure the complex dielectric function of NiO, ZnO, Ta
₂
O
₅
, and Nb
₂
O
₅
. These oxides were chosen for their efficacy as the tunneling insulator layer in a metal-insulator-metal (MIM) diode rectifier coupled to an antenna designed for high-frequency absorption. Specifically this work is aimed at a rectenna device designed for 1-THz operation. To further examine the merit of the oxides for rectifying high-frequency signals, the complex dielectric function was used to model the power transfer efficiency of an ac voltage source to a MIM diode. It was found that ZnO and NiO are candidate materials for high-frequency rectification with power transfer efficiency at 1 THz of 49% and 34%, respectively. For the same operating frequency, the other oxides show a poor coupling efficiency of 3.8% and 8% for Ta
₂
O
₅
and Nb
₂
O
₅
, respectively. It was also found that Ta
₂
O
₅
exhibits a sharp and distinct absorption at 0.48 and 1.24 THz.