Atomic layer deposited Al2O3 films for anti-reflectance and surface passivation applications

Al2O3 films were deposited on n-type crystalline Si (c-Si) wafers by atomic layer deposition using Al(CH3)3 and H2O as precursors. Surface anti-reflectance and passivation performances were investigated. Average reflectances between 2.8 and 4.2% were obtained for Al2O3 coated textured Si with Al2O3 thickness ranged between 100 and 70 nm. Wide thickness window for low reflectance between 2.8 and 4.2% indicates its potential anti-reflectance applications. A high minor carrier lifetime of ∼4.5 ms is obtained for n-type c-Si wafers passivated by 100 nm Al2O3 films, corresponding to an effective surface recombination velocity of ∼4 cm/s. Wide annealing time window and wide annealing temperature window are addressed to obtain good passivation performances with high minor carrier lifetime >3 ms. The passivation performances are related to the released H atoms from Al-OH bonds and the formation of Al vacancies and O interstitials within Al2O3 films. Our results indicate that Al2O3 films show dual functions of anti-reflectance and surface passivation for photovoltaic applications.