Electrical properties of spin coated ultrathin titanium oxide films on GaAs

recent years, ultrathin (<50 nm) metal oxide films have been being extensively studied as high-k dielectrics for future metal oxide semiconductor (MOS) technology. This paper discusses deposition of ultrathin TiO2 films (similar to 10 nm) on GaAs substrates (one sulfur-passivated, another unpassivated) by spin coating technique. The sulfur passivation is done to reduce the surface states of GaAs substrate. After annealing at 400 degrees C in a nitrogen environment, the TiO2 films are found to be polycrystalline in nature with rutile phase. The TiO2 films exhibit consistent grain size of 10-20 nmwith thickness around 10-12 nm. Dielectric constants of the films are found to be 65.4 and 47.1 corresponding to S-passivated and unpassivated substrates, respectively. Corresponding threshold voltages of theMOS structures are measured to be -0.1 Vto -0.3 V for the S-passivated and unpassivated samples, respectively. The S-passivated TiO2 film showed improved (lower) leakage current density (5.3 x 10(-4) A cm(-2) at 3 V) compared to the unpassivated film (1.8 x 10(-3) A/cm(2) at 3 V). Dielectric breakdown-field of the TiO2 films on S-passivated and unpassivated GaAs samples are found to be 8.4 MV cm(-1) and 7.2 MV cm(-1) respectively.