Dresden 2003 – scientific programme
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DS: Dünne Schichten
DS 23: Elektrische und optische Eigenschaften II
DS 23.3: Talk
Thursday, March 27, 2003, 15:45–16:00, GER/38
Electronic structure of silicon based heterojunctions used for solar cells — •Andreas Schöpke, Manfred Schmidt, Oliver Milch, and Walter Fuhs — Hahn Meitner Institut, Kekulestr.5, 12489 Berlin, Abt. Silizium Photovoltaik
One focal point of our research activities are silicon based hetero-solarcells like a-Si/c-Si and TCO/c-Si solar cells. For such heterostructures the energetic distribution of gap states, interface states and the band offsets play a crucial role.
Strong monochromatic UV-light (7eV) was used for the UPS measurement of the gap state distribution of phosphorous doped and undoped a-Si:H emitter layers deposited on c-Si by PE-CVD. The increase of N(E) with the doping and the shift of the Fermi level towards the conduction band is clearly shown. The variation of the doping level from 0 to 20000 ppm PH3 addition results in an increases of the Urbach energy from 51meV to 101meV and in an increase of the gap state density at midgap from 3 × 1018 cm−3eV−1 to 2 × 1019 cm−3eV−1.
The UV-PES method is the only way to determine all these quantities in such thin layers including the first stages of film growth. We will discuss the results in comparison to the results obtained with classical methods as photoconductivity yield for thick (120nm) a-Si:H layers.