Berlin 2015 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 63: Group IV elements and compounds

HL 63.2: Talk

Thursday, March 19, 2015, 09:45–10:00, EW 015

Valence band offset in heterojunctions between crystalline silicon and amorphous silicon (sub)oxides — •Martin Liebhaber, Mathias Mews, Tim Schulze, Lars Korte, and Klaus Lips — HZB, Institute Silicon Photovoltaics, Kekuléstr. 5, 12489 Berlin

The heterointerface between amorphous silicon (sub)oxides (a-SiO_x:H, 0<x<2) and crystalline silicon (c-Si) is investigated.

By varying SiH₄/CO₂ precursor gas mixtures, the stoichiometry of chemical-vapor-grown a-SiO_x:H layers was controlled, starting from pure a-Si:H to near-stoichiometric a-SiO₂. In-system photoelectron spectroscopy was employed to measure the valence band offset ΔE_V, while the defect density D_it, at the a-SiO_x/c-Si interface was determined using photoconductance decay.

We measure a systematic increase of ΔE_V starting from the established value of 0.3 eV for a-Si:H/c-Si to 4.3 eV for the a-SiO₂/c-Si heterojunction. Concomitantly the electronic quality (D_it) of the heterointerface deteriorates. For carrier transport across the a-SiO_x:H/c-Si heterojunction ΔE_V determines the barrier height for thermionic emission and/or tunneling of holes. Therefore the application of silicon suboxides in high-efficiency heterojunction solar cells seems to be unsuitable, mainly due to electronic transport hindrance resulting from the large ΔE_V, as also predicted by modeling studies [1].

The established analysis scheme can be readily applied to other types of heterojunctions, e.g. to promising silicon/metal oxide junctions [2].

[1] A. Kanevce et al., J. Appl. Phys. 105, 094507 (2009).

[2] C. Battaglia et al., Appl. Phys. Lett. 104, 113902 (2014).