Dresden 2011 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 44: Poster Session I

HL 44.16: Poster

Dienstag, 15. März 2011, 18:00–21:00, P3

Paramagnetic surface-states in µc-3C-SiC as efficient acceptor in solar cells — •Andre Konopka, Siegmund Greulich-Weber, Uwe Gerstmann, Eva Rauls, and Wolf Gero Schmidt — Physics, University of Paderborn, Paderborn, Germany

Microcrystalline silicon carbide (µc-SiC) have become an attractive new class of advanced microstructured materials for heterojunction photovoltaic (PV) devices due to their wide band gap and lower absorption in the visible region while retaining their higher conductivity. We use a sol-gel process for growing µc-SiC with sizes up to several 100 µm allowing arbitrary doping. The initial material is insulating, indicating that the resulting sol-gel SiC is almost free from usually unavoidable nitrogen donors. As an analytic tool for the control of doping success we used electron paramagnetic resonance (EPR). The spectra obtained are clearly different from those known for usual shallow donors and acceptors in bulk SiC. Obviously, in microcrystals at least some of the defects seen by EPR are no longer bulk-like, but are surface-related. PV measurements support our finding that the required acceptor behavior of µc-SiC is caused by surface-related defects in combination with an appropriate position of the fermi level, which is determined by donor or acceptor doping. Based on this knowledge, the microscopic structure of the responsible defect structure at the clean surface of the microcrystallites is discussed with the help of total energy calculations in the framework of density functional theory. For possible dangling-bond related structures the elements of the electronic g-tensor are calculated and compared with the experimental values.