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Activation Energy of Negative Fixed Charges in Thermal ALD Al2O3

: Kühnhold-Pospischil, S.; Saint-Cast, P.; Richter, A.; Hofmann, M.


Applied Physics Letters 109 (2016), Art. 061602
ISSN: 0003-6951 (Print)
ISSN: 1077-3118
Journal Article
Fraunhofer ISE ()
PV Produktionstechnologie und Qualitätssicherung; Photovoltaik; Silicium-Photovoltaik; Oberflächen: Konditionierung; Passivierung; Lichteinfang; Passivierung; Al2O3; Aktivierungsenergie

A study of the thermally activated negative fixed charges Qtot and the interface trap densities Dit at the interface between Si and thermal atomic-layer-deposited amorphous Al 2 O 3 layers is presented. The thermal activation of Qtot and Dit was conducted at annealing temperatures between 220°C and 500°C for durations between 3 s and 38 h. The temperature-induced differences in Qtot and Dit were measured using the characterization method called corona oxide characterization of semiconductors. Their time dependency were fitted using stretched exponential functions, yielding activation energies of EA = (2.2±0.2) eV and EA = (2.3±0.7) eV for Qtot and Dit, respectively. For annealing temperatures from 350°C to 500°C, the changes in Qtot and Dit were similar for both p- and n-type doped Si samples. In contrast, at 220°C the charging process was enhanced for p-type samples. Based on the observations described in this contribution, a charging model leading to Qtot based on an electron hopping process between the silicon and Al 2 O 3 through defects is proposed.