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Epitaxial growth of high quality n-type silicon foils in a quasi-inline APCVD reactor

: Milenkovic, N.; Rachow, T.; Janz, S.; Reber, S.

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Energy Procedia 77 (2015), S.613-618
ISSN: 1876-6102
International Conference on Crystalline Silicon Photovoltaics (SiliconPV) <5, 2015, Constance>
Zeitschriftenaufsatz, Konferenzbeitrag, Elektronische Publikation
Fraunhofer ISE ()

Reduction of solar cell fabrication costs is still of importance and can be achieved by going towards thinner silicon wafers. The aim is to achieve thicknesses in the range of 100 mu m and below while avoiding further kerf loss. The approach using porous silicon as a sacrificial detachment layer and as a seed layer for epitaxial growth can accomplish that goal [1]. Several research groups have already shown the high potential of this technique [2]. Most processes have been conducted in microelectronic-grade batch or single-wafer reactors, questioning the industrial feasibility of this concept. In this work n-type silicon wafers, epitaxially grown in a quasi-inline Atmospheric Pressure Chemical Vapour Deposition (APCVD) reactor, will be presented. The wafers were characterized using confocal white light microscopy, quasi steady state photoconductance decay (QSSPC), microwave detected photoconductance decay (MWPCD) and spreading resistance profiling (SRP) measurements. The first batch of n-type wafers showed mean effective carrier lifetimes exceeding 100 mu s on 45 x 45 mm(2) and locally more than 300 mu s. A detailed analysis on the thickness distribution, bulk lifetime and surface recombination velocity, affecting the effective carrier lifetime was conducted. For the second batch of n-type wafers mean effective carrier lifetimes of over 260 mu s on 25 x25 mm(2) and locally over 500 mu s were determined. This corresponds to a local bulk lifetime of over 800 mu s and shows the high material quality of epitaxial layers grown in our developed APCVD reactors.