Improving the Silicon Surface Passivation by Aluminum Oxide Grown Using a Non-Pyrophoric Aluminum Precursor

In this work, an alternative nonpyrophoric Al-precursor [dimethylaluminum isopropoxide (DMAI)] is used to deposit Al2O3 on p-type c-Si by plasma-enhanced and thermal atomic layer deposition (ALD). Al2O3 films grown by thermal ALD provide a relatively modest level of crystalline silicon surface passivation compared to their plasma-assisted ALD grown counterparts. This difference is attributed to a significant difference in the interfacial SiOx film as identified by Brewster's angle Fourier transform infrared spectroscopy. The energy barrier for DMAI to react with Si-H groups on the surface is significantly lower compared to TMA, which impedes the formation of the interfacial SiOx layer. As thermal ALD is the strongly preferred method in the photovoltaic industry, there is a strong incentive to improve the performance of the thermal ALD process to allow for the application of this intrinsically safer Al2O3 deposition process. A chemically grown thin oxide is shown to significantly improve the level of surface passivation provided by the thermal ALD Al2O3 film resulting in an increase in implied open circuit voltage from 653 to 723mV. This surface pretreatment thus solves a major barrier for the application of this intrinsically safer process in the photovoltaic industry.