Effects of polycrystalline GeO2 substrates on the structural, optical and electrical properties of ZnSe thin films

Abstract

Herein, the effects of polycrystalline germanium dioxide substrates on the structural, morphological, optical and electrical properties of zinc selenide thin films are reported. Thin films of ZnSe coated onto GeO2 are prepared by the thermal evaporation technique under vacuum pressure of 10–5 mbar. Compared to films grown onto glass substrates, ZnSe films deposited onto GeO2 exhibited narrower band gap and improved light absorbability. When ZnSe films are recoated onto gold substrates, the insertion of GeO2 layers between Au and ZnSe shifted the resonance peaks of the capacitance spectra from 527 to 711 MHz and formed new peak at 1000 MHz making the Au/ZnSe interfaces more appropriate for use as microwave cavities and as negative capacitance sources. Analysis of the conductivity spectra in the frequency domain of 10–1800 MHz revealed the domination of quantum mechanical tunneling and correlated barriers hoping of charge carriers in the samples. The fitting of the conductivity spectra assuming combined current conduction by these two mechanisms has shown that GeO2 layers increased the density of state near the Fermi level and shortened the scattering time of charge carriers. The designed Au/GeO2/ZnSe/C devices are also found to be suitable as band pass/stop filters. The notch frequency of these filters is shifted from 1420 MHz to 1050 MHz as a result of GeO2 participation in the structure of the Au/ZnSe devices.