Pronounced Impact of <i>p</i>-Type Carriers and Reduction of Bandgap in Semiconducting ZnTe Thin Films by Cu Doping for Intermediate Buffer Layer in Heterojunction Solar Cells
Waqar Mahmood,
Saif Ullah Awan,
Amad Ud Din,
Junaid Ali,
Muhammad Farooq Nasir,
Nazakat Ali,
Anwar ul Haq,
Muhammad Kamran,
Bushra Parveen,
Muhammad Rafiq,
Nazar Abbas Shah
Affiliations
Waqar Mahmood
Material Synthesis & Characterizations (MSC) Laboratory, Department of Physics, Fatima Jinnah Women University (FJWU), The Mall Rawalpindi 46000, Pakistan
Saif Ullah Awan
Department of Electrical Engineering, NUST College of Electrical and Mechanical Engineering, National University of Science and Technology (NUST), Islamabad 44000, Pakistan
Amad Ud Din
Analog Electronics System (AES) Laboratory, Department of Physics, Fatima Jinnah Women University (FJWU), The Mall Rawalpindi 46000, Pakistan
Junaid Ali
Department of Physics, COMSATS University Islamabad (CUI), Islamabad 44000, Pakistan
Muhammad Farooq Nasir
Department of Physics, RIPHAH International University, Islamabad 44000, Pakistan
Nazakat Ali
Department of Materials Science & Engineering, Institute of Space Technology (IST), Islamabad Highway, Islamabad 44000, Pakistan
Anwar ul Haq
Department of Physics, Govt. Postgraduate College (Boys) Satellite Town, Rawalpindi 46000, Pakistan
Muhammad Kamran
Department of Physics, COMSATS University Islamabad (CUI), Islamabad 44000, Pakistan
Bushra Parveen
Department of Physics, Lahore Garrison University, Lahore 54000, Pakistan
Muhammad Rafiq
Department of Mathematics, COMSATS University Islamabad (CUI) Wah Campus, Wah Cantt 47040, Pakistan
Nazar Abbas Shah
Thin Films Technology (TFT) Research Laboratory, Department of Physics, COMSATS University Islamabad (CUI), Islamabad 44000, Pakistan
Stabilized un-doped Zinc Telluride (ZnTe) thin films were grown on glass substrates under vacuum using a closed space sublimation (CSS) technique. A dilute copper nitrate solution (0.1/100 mL) was prepared for copper doping, known as an ion exchange process, in the matrix of the ZnTe thin film. The reproducible polycrystalline cubic structure of undoped and the Cu doped ZnTe thin films with preferred orientation (111) was confirmed by X-rays diffraction (XRD) technique. Lattice parameter analyses verified the expansion of unit cell volume after incorporation of Cu species into ZnTe thin films samples. The micrographs of scanning electron microscopy (SEM) were used to measure the variation in crystal sizes of samples. The energy dispersive X-rays were used to validate the elemental composition of undoped and Cu-doped ZnTe thin films. The bandgap energy 2.24 eV of the ZnTe thin film decreased after doping Cu to 2.20 eV and may be due to the introduction of acceptors states near to valance band. Optical studies showed that refractive index was measured from 2.18 to 3.24, whereas thicknesses varied between 220 nm to 320 nm for un-doped and Cu doped ZnTe thin film, respectively, using the Swanepoel model. The oxidation states of Zn+2, Te+2, and Cu+1 through high resolution X-ray photoelectron spectroscopy (XPS) analyses was observed. The resistivity of thin films changed from ~107 Ω·cm or undoped ZnTe to ~1 Ω·cm for Cu-doped ZnTe thin film, whereas p-type carrier concentration increased from 4 × 109 cm−2 to 1.4 × 1011 cm−2, respectively. These results predicted that Cu-doped ZnTe thin film can be used as an ideal, efficient, and stable intermediate layer between metallic and absorber back contact for the heterojunction thin film solar cell technology.
