Charge Density in Atmospheric Pressure Chemical Vapor Deposition TiO(2) on SiO(2)-Passivated Silicon

The charge density of a TiO(2) film deposited on a SiO(2)-passivated silicon wafer is determined. The TiO(2) is deposited by atmospheric pressure chemical vapor deposition at 400 degrees C, and the SiO(2) is grown thermally at 950 degrees C. This TiO(2)-SiO(2) 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 SiO(2)-Si interface. While these properties are beneficial to high efficiency solar cells, so too is a large charge density, as what occurs in Si(3)N(4)-SiO(2) (+10(12) cm(-2)) and Al(2)O(3)-SiO(2) (-10(13) cm(-2)) stacks. The D(it)(E) and charge density of TiO(2)-coated and SiO(2)-passivated silicon are evaluated by capacitance-voltage and Kelvin probe measurements. The charge density of the TiO(2) is within the conservative limits of -8.5 and -1 x 10(11) cm(-2) after deposition and of -10 and +1 x 10(11) cm(-2) after a subsequent 800 degrees C oxygen anneal. Photoconductance measurements suggest that the dangling-bond defects at the SiO(2)-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. (C) 2009 The Electrochemical Society. [DOI:10.1149/1.3216029] All rights reserved.