Gamma-radiation hardness and long-term stability of ALD-Al2O3 surface passivated Si

Al2O3 has emerged as the surface passivation material of choice for p-type silicon in photovoltaics and has also become a candidate for passivating Si-based radiation sensors. However, the surface passivation of Al2O3 has been shown to degrade when exposed to gamma-radiation, making it of interest to determine methods of depositing Al2O3 that minimize the radiation-induced degradation on the surface passivation. In this study, we investigate the long-term stability and gamma-radiation hardness of Al2O3 prepared using the TMA+H2O+O-3 precursor combination and how the pretreatment, the deposition temperature, and the film thickness affect the density of interface states, Dit, and fixed oxide charge, Qfix, before and after gamma-irradiation. We find that the surface saturation current density, J(0s), of silicon passivated by Al2O3 increases after annealing but stabilizes over time depending on the Al2O3 thickness. Samples with thicknesses of <20 nm stabilize within hours, while those with >60 nm stabilize over days. J(0s) stabilizes at lower values with increased Al2O3 thickness. After exposure to 1 Mrad gamma-radiation, the samples still exhibit low D-it and high Q(fix), with the best performing sample having a Dit of 1.5 x 10(10) eV(-1) cm(-2) and a Qfix of -3.1 x 10(12) cm(-2). The deposition temperature appears to indirectly affect radiation hardness, owing to its impact on the hydrogen concentration in the film and at the Si-SiOx-Al2O3 interface. Lifetime measurements after irradiation indicate that Al2O3 still passivates the surface effectively. The carrier lifetime and Qfix can largely be recovered by annealing samples in O-2 at 435 degrees C.