Berlin 2005 – wissenschaftliches Programm

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HL: Halbleiterphysik

HL 17: Poster Ib

HL 17.23: Poster

Freitag, 4. März 2005, 16:30–19:00, Poster TU F

Defect analysis at the a-Si:H/c-Si heterojunction — •Abdelazize Laades, Lars Korte, Karsten v. Maydell, Christian Schubert, Klaus Kliefoth, Manfred Schmidt, and Walther Fuhs — Hahn-Meitner-Institut Berlin, Silizium-Photovoltaik, Kekuléstr. 5, D-12489 Berlin

Ultrathin undoped hydrogenated amorphous silicon (a-Si:H) layers (thickness ≈ 10 nm) were deposited by plasma-enhanced chemical vapor deposition on p-doped crystalline silicon wafers. The density of states at the a-Si:H/c-Si(p) interface was investigated by field-dependent surface photovoltage (FD-SPV) and photoluminescence (PL) techniques. Photoelectron yield spectroscopy (PEYS) has been applied to determine the density of states N(E) within the ultrathin a-Si:H films.

By means of FD-SPV, the energetic distribution of the interface trap density D_it(E) could be determined. However, at room temperature the measurement is strongly influenced by recharging effects in a-Si:H. This effect can be reduced by cooling the sample down to 100 K.

D_it(E) consists of a continuum with a characteristic curvature extending towards the band edges. The minimum of D_it(E) is as low as 2×10¹¹ eV⁻¹cm⁻² at mid-gap. This demonstrates the excellent passivation of the silicon surface by a-Si:H. Applying PEYS, the Fermi energy and the gap state distribution (density of dangling bonds at mid-gap and Urbach energy of the tail states) in the a-Si:H film were measured. We will discuss the complex relationship between the values of N(E) and D_it(E) measured with both methods.