Enhanced Electrical Properties Of P-type SnO₂ Thin Films By In-Al Co-doping

Transparent conducting oxide films have been used extensively in many applications such as the window layers of solar cells, as front electrodes in flat panel displays (FPD), gas sensors, antistatic coatings, SIS heterogeneity junction, EC-windows for privacy etc, which due to its low resistivity, high optical transparency, high reflectance in the infrared region and its semiconductor characteristics. Although the TCOs have a vast range of applications as mentioned above, very little work has been done on active device fabrication using TCOs. This is because most of the aforementioned TCOs are n-type semiconductors. But the corresponding p-type transparent conducting oxides (p-TCO) are essential for junction devices.Here we have tried to give a comprehensive and up-to-date picture of this interesting and challenging field of p-type transparent conducting oxides. The property, application and p-type doping mechanism of SnO₂ were also introduced. The first principle calculation had been performed for SnO₂ supercells. The results showed that In-Al co-doped SnO₂ will reduce the lattice distortion effect induced by In impurity, and increase the hole mobility. Based on the theoretical results, p-type transparent conductive In-Al co-doped SnO₂ thin films were successfully prepared by DC reactive magnetron sputtering. The films were fabricated by two-step method: alloy films were deposited and then thermally oxidized in the air at high temperature. And the processing parameters were characterized systematically. The films with transmittance over 80% in the visible region and hole concentration as high as 6.43×10¹⁸cm^-3 were obtained. In addition, the films were prepared by reactive DC magnetron sputtering under different parameters, but the electrical properties and the crystalline properties of the films are inferior to the films fabricated by the two-step method mentioned above. The transmittances were over 90% in the visible region.