Semiconductor Physics, Quantum Electronics & Optoelectronics. 2014. V. 17, N 3. P. 275-283.
Optical and structural studies of phase transformations and composition fluctuations at annealing of Zn1-xCdxO films
grown by dc magnetron sputtering
1V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine,
Abstract. Ternary Zn1-xCdx O (x 〈 0.12) alloy crystalline films with highly preferred orientation (002) have been successfully deposited on sapphire c-Al2O3 substrates using the direct current (dc) reactive magnetron sputtering technique and annealed at temperature 600 °C in air. The structural and optical properties of Zn1-xCdxO thin films were systematically studied using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), micro-Raman and photoluminescent (PL) spectroscopy. XPS measurements clearly confirmed Cd incorporation into ZnO lattice. XRD data revealed that the growth of wurtzite Zn1-xCdxO films occurs preferentially in the (002) direction. Also, when the Cd content is increased, the XRD peaks shift towards smaller angles and the full width at half-maximum of the lines increases. When the Cd content increases, A 1 LO ( Zn1-xCdxO )-like Raman modes show composition dependent frequency decrease and asymmetrical broadening. The near band-edge PL emission at room temperature shifts gradually to lower energies as the Cd content increases and reaches 2.68 eV for the highest Cd content (x = 0.12). The analysis of NBE band emission and Raman A 1 LO ( Zn1-xCdxO) mode shows that at a higher Cd content the coexistence of Zn1-xCdxO areas with different concentrations of Cd inside the same film occurs. The presence of CdO in annealed Zn1-xCdxO films with the higher Cd content was confirmed by Raman spectra of cubic CdO nanoinclusions. The XRD data also revealed phase segregation of cubic CdO in annealed Zn1-xCdxO films (Tann = 600 °C) for x 〉 0.013.
Keywords:Zn1–xCdxO films, XRD, XPS, Raman spectroscopy, photoluminescence, phase segregation.
Manuscript received 07.03.14; revised version received 27.06.14; accepted for publication 16.09.14; published online 30.09.14.