Growth and characterisation of n- and p-type ZnTe thin films for applications in electronic devices

Growth and characterisation of n- and p-type ZnTe thin films forapplications in electronic devicesO.I. Olusolaa,b,*, M.L. Madugua, N.A. Abdul-Manafa, I.M. DharmadasaaaElectronic Materials and Sensors Group, Materials and Engineering Research Institute, Sheffield Hallam University, Sheffield S1 1WB, United KingdombDepartment of Physics, School of Science, The Federal University of Technology, FUTA, Akure P.M.B. 704, Nigeriaarticle infoArticle history:Received 8 July 2015Received in revised form16 October 2015Accepted 4 November 2015Available online 7 November 2015Keywords:Electrodepositionn-type ZnTep-type ZnTeIntrinsic dopingZnTe homo-junction diodeabstractThe growth of n- and p-type ZnTe thin films have been achieved intrinsically by potentiostatic elec-trodeposition method using a 2-electrode system. Cyclic voltammogram have been used to obtain rangeof growth voltages required to form stoichiometric thin films of ZnTe. The ZnTe thin films have beenelectrodeposited (ED) on glass/fluorine-doped tin oxide (FTO) conducting substrates in aqueous solutionsof ZnSO4$7H2O and TeO2. The films have been characterised for their structural, electrical, morphological,compositional and optical properties by using X-ray diffraction (XRD), Raman spectroscopy, Photo-electrochemical (PEC) cell measurements, DC conductivity measurements, Scanning electron microscopy(SEM), Atomic force microscopy (AFM), energy-dispersive X-ray analysis (EDX) and Optical absorptiontechniques. The XRD results reveal that the electroplated films are polycrystalline and have hexagonalcrystal structure with the preferred orientation along (002) plane. UVeVisible spectrophotometer hasbeen used for the bandgap determination of as-deposited and heat-treated ZnTe layers. The bandgap ofthe heat-treated ZnTe films are in the range (1.90e2.60) eV depending on the deposition potential. PECcell measurements show that the ED-ZnTe films have both n- and p-type electrical conductivity. The DCconductivity measurements revealed that the average resistivity of n-ZnTe and p-ZnTe layers of equalthickness is of the order of 104Ucm; the magnitude of the electrical resistivity of p-ZnTe is almost fivetimes greater than that of the n-ZnTe layer. Using the n- and p-type ZnTe layers, p-n homo-junctiondiodes with device structure of glass/FTO/n-ZnTe/p-ZnTe/Au were fabricated. The fabricated diodesshowed rectification factor of 102, reverse saturation current of ~10.0 nA and potential barrier heightgreater than 0.77 eV indicating electronic device quality of these layers