High Broadband Optical Absorption and Bandstop Filter Characteristics of Pb/Nb 2 O5 Interfaces

Abstract

In this study, semitransparent lead films serve as substrates for depositing niobium pentoxide thin films, forming versatile electro-optical devices. Using vacuum evaporation and ion sputtering techniques at ≈10−5 mbar, stacked layers of crystalline Pb and amorphous Nb2 O5 are created. This process reduces free carrier absorption in Nb2 O5 and forms Urbach tail states with a width of 0.91 eV. Pb/Nb 2 O5 thin films exhibit remarkable broad band absorption, exceeding 440% in the visible and 98% in the infrared. Moreover,Pb substrates induce a redshift in Nb 2 O5 ’s energy bandgap. Electrical analysis using impedance spectroscopy on Pb/Nb 2 O5 /Ag structures reveals their series/parallel resonance and bandstop filter properties. Notably, the bandstop filters exhibit reflection coefficient minima at a notch frequency of1.66 GHz, with a bandwidth of 280 MHz, return loss of 26 dB, and voltage standing wave ratio of 1.13. These findings underscore the device’s potential for wide-ranging electro-optical applications across the electromagnetics pectrum