Al2O3 passivation on c-Si surfaces for low temperature solar cell applications

Functional passivation of high resistivity p-type c-Si wafer surfaces was achieved using 10 nm Al2O3 layers and low temperatures for both the thermal ALD process and post-deposition anneal. Effective lifetime values higher than 1 ms were measured at excess carrier density Delta n=10(15) cm(-3). This result was reached in combination with temperatures of 100 degrees C and 200 degrees C for the Al2O3 layer deposition and anneal, respectively. The Al2O3/c-Si interface was characterized using conductance-voltage and capacitance-voltage measurements. In particular, significantly reduced interface density of the electrically active defects D-it similar to 2 x 10(10) eV(-1)cm(-2) was detected, which enabled excellent chemical passivation. The measured density of fixed charges at the interface, Q(f), after anneal were in the range + 1 x 10(12) to -1 x 10(12) cm(-2) indicating that both inversion and accumulation conditions result in relevant field-effect passivation using Al2O3 layers and low temperature processes. Numerical simulations on representative test structures show that the uniform Q(f) effect can be understood in terms of a surface damage region (SDR) present near the interface in combination with asymmetry in the lifetime of holes and electrons in the SDR. The combination of low processing temperatures, thin layers and good passivation properties facilitate a technology for future low temperature solar cell applications. (C) 2013 The Authors. Published by Elsevier Ltd.