Charge density in atmospheric pressure chemical vapor deposition TiO ₂ on SiO₂ -passivated silicon

The charge density of a TiO₂ film deposited on a SiO₂ -passivated silicon wafer is determined. The TiO₂ is deposited by atmospheric pressure chemical vapor deposition at 400°C, and the SiO2 is grown thermally at 950°C. This TiO₂ - SiO₂ stack is a useful coating for the front surface of a silicon solar cell, as it has a high optical transmission and a low density of interface states D_it (E) at the SiO₂ -Si interface. While these properties are beneficial to high efficiency solar cells, so too is a large charge density, as what occurs in Si₃ N₄ - SiO₂ (+ 10¹² cm ^-2) and Al₂ O₃ - SiO₂ (- 10 ¹³ cm^-2) stacks. The D_it (E) and charge density of TiO₂ -coated and SiO2 -passivated silicon are evaluated by capacitance-voltage and Kelvin probe measurements. The charge density of the TiO₂ is within the conservative limits of -8.5 and -1× 10 ¹¹ cm^-2 after deposition and of -10 and +1× 1011 cm-2 after a subsequent 800°C oxygen anneal. Photoconductance measurements suggest that the dangling-bond defects at the SiO₂ -Si interface are predominantly donorlike and, hence, that the change density in the TiO ₂ is closer to the upper limits (less negative); this charge is too small to benefit solar cells.