Impact of metal-organic vapor phase epitaxy environment on silicon bulk lifetime for III–V-on-Si multijunction solar cells

With the final goal of integrating III–V materials on silicon substrates for tandem solar cells, the influence of the metal-organic vapor phase epitaxy (MOVPE) environment on the minority carrier properties of silicon wafers has been evaluated. These properties will essentially determine the photovoltaic performance of the bottom cell in a III–V-on-Si tandem solar cell. A comparison of the base minority carrier lifetimes obtained for different thermal processes carried out in a MOVPE reactor on Czochralski silicon wafers has been carried out. An important degradation of minority carrier lifetime during the surface preparation (i.e. H2 anneal) has been observed. Three different mechanisms have been proposed for explaining this behavior: (1) the introduction of extrinsic impurities coming from the reactor; (2) the activation of intrinsic lifetime killing impurities coming from the wafer itself; and finally, (3) the formation of crystal defects, which eventually become recombination centers. The effect of the emitter formation by phosphorus diffusion has also been evaluated. In this sense, it has been reported that lifetime can be recovered during the emitter formation either by the effect of the P on extracting impurities, or by the role of the atomic hydrogen on passivating the defects. •We have studied the evolution of the minority carrier lifetime during the optimization of the bottom subcell.•For this analysis it has been used different wafer types (i.e. Fz and Cz) and different wafer suppliers.•Samples have been characterized using Photoconductance Decay equipment.•An important lifetime degradation is observed during the initial annealing of the samples (i.e. hydrogen atmosphere).•An interesting lifetime recovery was observed during the formation of the emitter by PH3 diffusion.