Investigation of Al2O3 Passivation Layers by Photoluminescence Imaging under Applied Voltage

In this work, the passivation properties of Al2O3 thin films deposited by atomic layer deposition on p-type Si substrates has been studied by photoluminescence imaging under applied bias (PL-V). By measuring the carrier lifetime as a function of voltage this method enables investigations of the recombination properties of the Al2O3/c-Si interface under various band bending conditions in a simple and reproducible manner. The results were interpreted in the framework of the extended Shockley-Read-Hall theory using the fixed charge density and surface recombination velocity parameters 0 and 0 as fitting parameters. The extracted values were also found to be in good agreement with results from capacitance-voltage measurements. A high carrier lifetime above 1.5 ms was obtained with the traditionally used precursors Trimethylaluminum (TMA) and ozone (O3), producing layers with a large negative of −4×1012 cm-2. Samples were also deposited using a combination of TMA and the low-cost alternative precursor dimethylaluminium chloride (DMACl), also providing good passivation with carrier lifetimes over 1 ms on Cz substrates. For these samples, , 0 and 0 were all observed to decrease with increasing deposition temperature from 100 °C to 300 °C, with the best passivation quality obtained at 300 °C. For all the investigated samples 0 was found to be larger than 0 by a factor between 2 and 5.