ZnO Thin Films of High Crystalline Quality Deposited on Sapphire and GaN Substrates by High Temperature Sputtering
- PDF / 264,511 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 10 Downloads / 217 Views
ZnO Thin Films of High Crystalline Quality Deposited on Sapphire and GaN Substrates by High Temperature Sputtering Michaá A. Borysiewicz1, Iwona Pasternak1, ElĪbieta Dynowska1,2, Rafaá Jakieáa2, Marek Wzorek1, Valery Kolkovski2, Anna DuĪyĔska2, Eliana KamiĔska1, Anna Piotrowska1 1 2
Institute of Electron Technology, Al. Lotników 32/46, 02-668 Warsaw, Poland Institute of Physics, PAS, Al. Lotników 32/46, 02-668 Warsaw, Poland
ABSTRACT Single orientation ZnO (00.2) films were deposited by means of high temperature high vacuum reactive magnetron sputtering onto Al2O3 (0001) and GaN (0001) substrates. In order to obtain films of high crystalline quality a novel approach to ZnO sputter deposition was employed, adapting the practice used in MBE technology, of using a MgO buffer layer deposited on sapphire at a high-temperature followed by a ZnO nucleation layer deposited at low temperature. ZnO films were also grown on epitaxial GaN/Al2O3 substrates where the GaN layer was treated as the buffer layer. Following the deposition, all samples were annealed ex-situ in an O2 flow at 800oC. The obtained ZnO films have a lattice constant c equal to 5.2036 Å and 5.214 Å for the films deposited on Al2O3 and GaN substrates, respectively. Secondary ion mass spectroscopy depth profiles, scanning and transmission electron microscopy cross sectional images and atomic force microscope were used to characterize the structural properties of the films. Electrical properties were assessed using Hall effect measurement. Photoluminescence spectra were also taken. INTRODUCTION A substrate of choice for thin film ZnO deposition is the widely accessible and costeffective sapphire. However, although Al2O3 and ZnO have the same hexagonal crystalline structure, the high lattice mismatch of 18% causes significant strain in the deposited ZnO/Al2O3 films. A possible solution to this problem used in MBE technology for ZnO/Al2O3 growth is the application of a thin MgO buffer layer which diminishes the lattice mismatch [1-3]. With the recent advancements in the technology of sputtering systems, especially the high precision ultra high vacuum systems, it was possible to think of an adaptation of this technique to sputtering deposition of thin ZnO films. The results of this adaptation are described in the first part of this work. The second part covers a modification of this approach, using a 3 ȝm thick epitaxial GaN film on Al2O3 as a buffer layer for ZnO growth. EXPERIMENT The Al2O3 (0001) and epitaxial GaN/Al2O3 (0001) substrates were cleaned by boiling in trichloroethylene, acetone and 2-propanol, rinsed with deionised water and blown dry with N2 gas. The sapphire substrates were subsequently annealed for 20 minutes in an oxygen flow at 800oC. The following deposition scheme was used for films deposited onto Al2O3 substrates: 1. 1 nm thick MgO buffer layer deposition at 850oC
113
2. 6 nm thick low temperature ZnO (ZnOLT) nucleation layer deposition at 350oC 3. in-situ annealing in vacuum at 750oC for 5 minutes for surface smoothing 4. 240 nm thick
Data Loading...
