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In this Letter, we report that both thermal atomic layer deposition (ALD) with H2O, and plasma ALD with an O2 plasma, can be used to deposit Al2O3 for a high level of surface passivation of crystalline silicon (c‐Si). For 3.5 Ω cm n‐type c‐Si, plasma ALD Al2O3 resulted in ultralow surface recombination velocities of Seff < 0.8 cm/s. Thermal ALD Al2O3 also showed an excellent passivation level, with Seff < 2.5 cm/s. In contrast to plasma ALD Al2O3, thermal ALD Al2O3 provides some surface passivation in the as‐deposited state, although annealing is required to activate it to the full extent. For thermal ALD, the optimal temperature for this anneal was found to be slightly lower, ∼375 °C, than for plasma ALD Al2O3, ∼425 °C. The minimal Al2O3 thickness without compromising the passivation properties was 5 nm for plasma ALD Al2O3, whereas for thermal ALD, films >10 nm were required. Thermal stability against a high temperature firing step was demonstrated for ultrathin thermal and plasma ALD Al2O3 films of 5 nm by Seff < 9.2 and < 6.5 cm/s, respectively. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The thermal and ultraviolet (UV) stability of crystalline silicon (c-Si) surface passivation provided by atomic layer deposited Al2O3 was compared with results for thermal SiO2. For Al2O3 and Al2O3/a-SiNx:H stacks on 2 Ω cm n-type c-Si, ultralow surface recombination velocities of Seff&lt;3 cm/s were obtained and the passivation proved sufficiently stable (Seff&lt;14 cm/s) against a high temperature “firing” process (&gt;800 °C) used for screen printed c-Si solar cells. Effusion measurements revealed the loss of hydrogen and oxygen during firing through the detection of H2 and H2O. Al2O3 also demonstrated UV stability with the surface passivation improving during UV irradiation.

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We apply ultra‐short pulse laser ablation to create local contact openings in thermally grown passivating SiO2 layers. This technique can be used for locally contacting oxide passivated Si solar cells. We use an industrially feasible laser with a pulse duration of τpulse ∼ 10 ps. The specific contact resistance that we reach with evaporated aluminium on a 100 Ω/sq and P‐diffused emitter is in the range of 0·3–1 mΩ cm2. Ultra‐short pulse laser ablation is sufficiently damage free to abandon wet chemical etching after ablation. We measure an emitter saturation current density of J0e = (6·2 ± 1·6) × 10−13 A/cm2 on the laser‐treated areas after a selective emitter diffusion with Rsheet ∼ 20 Ω/sq into the ablated area; a value that is as low as that of reference samples that have the SiO2 layer removed by HF‐etching. Thus, laser ablation of dielectrics with pulse durations of about 10 ps is well suited to fabricate high‐efficiency Si solar cells. Copyright © 2007 John Wiley & Sons, Ltd.