| Abstrakt: |
(CaxBay)F2(x:y=7:3, 1:1 and 3:7)/n-type InP (100) metal-insulator-semiconductor (MIS) structures were investigated by means of capacitance-voltage (C-V) measurements and X-ray photoelectron spectroscopy (XPS) to study the effect of the molar ratio (x:y) of the fluoride films on the quality of the interface between the fluoride and InP. The fluoride films were deposited on the InP substrates by co-evaporating CaF2and BaF2powders in a vacuum of about 1-2×10-6Torr. The best C-Vcharacteristics were obtained for the lattice-matched (CaBa)F2(Ca:Ba=1:1 in molar ratio)/InP and the next-best, for the (CaBa)F2(Ca:Ba=7:3)/InP MIS structures. On the other hand, poor C-Vcharacteristics were obtained for the (CaBa)F2(Ca:Ba=3:7)/InP and the SrF2/InP structures, though their lattice matchings were better than that of the (CaBa)F2(Ca:Ba=7:3)/InP structure. It is therefore concluded that the lattice matching between the fluoride film and the InP substrate is probably the most important factor for obtaining a good-quality interface; however, the presence of a fair amount of the "stable" Ca-P bonds is also effective to obtain a stable interface between fluoride and InP. The XPS data indicated that fluoride films with distinct and uniform chemical compositions were formed from the top surface to the interface with the InP substrate even by the conventional vacuum evaporation technique. The peak binding energy of the XPS signal from the Ba 3d core level shifts to the lower energy side, while that from the Ca 2p core level shifts to the higher energy side with increase in the ratio of Ba to Ca. These shifts are nearly linear with the change of the mixed molar ratio. These findings can be explained by a difference in ionic radii between Ba and Ca in the fluorite structure and indicate that the molar ratios in the fluoride films are the same as the mixed molar ratios of the source powders. Native oxides of InP such as In2O3, InPO3and InPO4were found to be removed or reduced by the fluoride films during or after deposition of these films. A small amount of oxygen was included in the fluoride film, indicating that the fluoride film reduced the native oxide of InP and became oxidized itself. |
