Material combination of Tunnel-SiO2 with a (sub-)Monolayer of ALD-AlOx on silicon offering a highly passivating hole selective contact

In this work, we investigate a passivating hole-selective tunnel contact on crystalline silicon (Si) based on an ultrathin thermal SiO2 and a (sub-)monolayer thick aluminum oxide (AlOx) deposited by atomic layer deposition (ALD) with 1 to 7 cycles. Rapid thermal annealing (RTA) is essential to activate the passivation and intense visible light is demonstrated to play a key role in the formation and occupation of the Al-induced acceptor states in SiO2 that provide the passivation. This simple stack provides very good surface passivation on n-type Si with a surface saturation current density as low as J(0s) = 25 IA/cm(2) (S-eff = 2.7 cm/s) and a contact resistivity rho(c) of similar to 200 m Omega cm(2), while being Si-dopant-free, fully transparent and firing-stable. The Al-deposition on thermal SiO2 during the initial ALD-cycles is studied carefully by synchrotron-based reference-free grazing incidence X-ray fluorescence spectrometry (GIXRF). Different metallization and capping approaches are tested and discussed.