GROWTH OF NONPOLAR PLANE ZINC OXIDE THIN FILMS AND DEFECT LEVEL DETECTION BY PHOTOTHERMAL DEFLECTION SPECTROSCOPY
127 , 2016-03-24 , 法政大学
To fabricate p-type ZnO thin films reproducibly and to apply to LED, nonpolar a-plane ZnO thin films doping with nitrogen (a-ZnO:N) have been deposited on r-plane sapphire substrates by metal organic chemical vapor deposition ( MOCVD ). To activate dopant atoms, ZnO films were annealed in atmospheric pressure oxygen. In growth of semiconductor thin films, it is important to find correlation between growth condition and defect of semiconductor thin film. Since it is needed to detect defect levels of semiconductor thin films sensitively, it has been set up the equipment of photothermal deflection spectroscopy ( PDS ) to detect defect levels in band gap of fablicated ZnO films. As-deposited a-ZnO:N films had very high N concentration of more than 1021cm-3 by suppling mix gas with N_2O and NO. The surface of as-deposited a-ZnO:N films was rough. Bandgap energy and band edge emission intensity of as-deposited a-ZnO:N films were declined. Annealing improve the quality of a-ZnO:N film which was deposited supplying NO gas at 0.5 sccm. The N concentration was maintained by more than 1019cm -3 even after annealing. In the electric characteristic evaluation such as thermal electromotive force evaluation and hall measurement, the annealed a-ZnO:N film showed p-type conductivity. Band line-up of N-doped ZnO before and after the annealing was determined by band gap energy and energy at maximum of valence band evaluated by x-ray photoelectron spectroscopy. Fermi level of a-ZnO:N films was shifted to the center of bandgap. The variation of band structure of annealed a-ZnO:N film contradicts the electric characteristic evaluation. It is considered that fermi level of the annealed a-ZnO:N film reflected impurities which contributed n-type conduction and precipitated on the surface. It is needed to perform sensitivive defect level evaluation to deepen understanding of band structure.