Al2O3 Passivation on c-si Surfaces for Low Temperature Solar Cell Applications

AbstractFunctional passivation of high resistivity p-type c-Si wafer surfaces was achieved using 10nm Al2O3 layers and low temperatures for both the thermal ALD process and post-deposition anneal. Effective lifetime values higher than 1ms were measured at excess carrier density Δn=1015cm-3. This result was reached in combination with temperatures of 100°C and 200°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 Dit ∼ 2 x 1010eV-1cm-2 was detected, which enabled excellent chemical passivation. The measured density of fixed charges at the interface, Qf, after anneal were in the range +1 x 1012 to -1 x 1012cm-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 Qf 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