Efficiency Potential Analysis of p- and n-Type Epitaxially Grown Si Wafers

In this paper, we investigate the quality of epitaxially grown, 110 mm thick, n- and p-type silicon (Si) layers deposited in a CVD batch reactor of microelectronic standard. Two types of wafers are characterized: 'EpiRef' grown on chemically and mechanically polished reference substrates and 'EpiWafer' grown on substrates with a porous silicon detachment layer. EpiRef wafers exhibit excellent minority carrier lifetimes of 2.5 ms for n-type and 1.3 ms for p-type. EpiWafers show reduced, but still promising lifetimes of 0.5 ms (in local areas up to 1 ms) for n-type and 40 ms for p-type. For EpiWafers, we found that quality limitations are due to stacking faults as well as interstitial iron contamination for p-type. An efficiency limiting bulk recombination analysis (ELBA), allows for an assessment of the corresponding efficiency potential assuming a TOPCon cell model with a cell limit of 25.9 % for n-type and a TOPCoRE cell model with a cell limit of 26.5 % for p-type. In selected 1 cm² areas, potential efficiencies of EpiRef wafers are only -0.4 %abs below the theoretical cell limit for n-type and -1.3 %abs for p-type whereas EpiWafers feature losses of -1.2 %abs for n-type and even -5.4 %abs for p-type.