The origin of emitter-like recombination for inverted c-Si surfaces

c-Si samples whose surface passivation is based on highly inverted surfaces experimentally show a decrease in effective lifetime at low illumination levels while a flat dependence is expected from the current theoretical understanding. As an explanation for this discrepancy we propose a defect-rich bulk region close to c-Si surface. From an analytical approach, we deduce that the final lifetime dependence is a combination between an emitter-like term and a quasi-neutral bulk recombination term. Next, we use numerical modeling to simulate eff(n) curves depending on damage depth, lifetime in the damaged region and the doping density. Simulations show that inverted surfaces in highly-doped substrates are more sensitive to shallow defect regions. On the other hand, very lowly doped c-Si substrates show a lifetime reduction at high injection and the presence of a small "hump" in the lifetime when overall recombination becomes Auger-dominated. Finally, we show that experimental eff(n) curves of a-SiNx:H and Al2O3 c-Si passivated c-Si samples demonstrate the predicted characteristics which could not properly be accounted for previously.