Inverting electrodeposited nanostructured Cu2O thin films from n-type to p-type semiconductors and variation of their physical and photoelectrochemical properties for optoelectronic applications

Abstract

Employing identical techniques to produce the semiconductor with n and p-type conductivity is one of the most important keys to fabricating higher performance optoelectronic devices. Therefore, here the electrodeposition technique was employed to grow nanostructured Cu2O thin films with different pH values ranging from 3.5 to 13 from the same precursors before starting the deposition process. The morphological, structural, optical, electrical, and photoelectrochemical properties of fabricated Cu2O thin films were investigated employing SEM, EDX, XRD, Raman, UV–Vis, PL, Photocurrent, Mott-Schottky, and electrochemical impedance spectroscopy (EIS) measurements. XRD results showed the formation of Cu, Cu2O, and CuO phases with low pH values, while only Cu2O phase is obtained with higher pH. Raman measurements proven phonon modes of nanostructured Cu2O thin films. The morphology varies with different shapes such as spherical, pyramids, and prisms according to pH values. The optical absorption edge has appeared between 475 nm and 575 nm which indicates the formation of Cu2O and the calculated band gap varies from 2 to 2.44 eV. PL measurements indicate two dominant peaks related to inter-band transitions and defects including copper interstitials. Photocurrent measurements denoted that samples with lower pH from 6 to 7.6 are n-type semiconductors, while higher ones from 8 to 13 are p-type semiconductors. Mott-Schottky measurements showed that the donor’s density declines from about 2 × 1017 cm− 3 to about 1.6 × 1016 cm− 3 as pH increases from 6 to 7.6 whereas the acceptor’s density rises from about 1.25 × 1017 cm− 3 to about 3 × 1018 cm− 3 as pH increases from 8 to 13. EIS results show that both p-type and n-type samples have higher separation and transfer of charge carriers. Our outcomes indicate that the electrodeposited nanostructured Cu2O thin films are appropriate materials for biosensors, solar cells, and supercapacitors applications.