Characterization of lanthanum-aluminum oxide thin films deposited by spray pyrolysis

The optical, electrical, and structural characteristics of lanthanum-aluminum oxide thin films deposited by ultrasonic spray pyrolysis are presented. The films were deposited using a lanthanum nitrate and aluminum acetylacetonate solution in N, N-dimethylformamide on (100) Si substrates. The substrate temperature during deposition was in the 500-650°C range. The deposition activation energy was in the range of 17.4-20 kJ mol-1, depending on the relative concentration of lanthanum to aluminum in the precursor solution. The films were amorphous even at 650° C and they were given no further temperature annealing. The refractive index at 630 nm was in the range of 1.70-1.755 depending on the amount of lanthanum in the films. The electrical characteristics of the films were determined from capacitance and current versus voltage measurements of metal-oxide-semiconductor (MOS) structures incorporating them. A dielectric constant in the range of 5.2-10, and interface states density of the order of 1011-1012 eV-1 cm-2 were measured. Their electrical breakdown field was in the range of 4.5-7.6 MVcm-1 for films deposited at 500 and 550°C and a thickness under 43 nm.