Structural investigation of ion implantation of boron on random pyramid textured Si(100) for photovoltaic applications

Abstract

Ion implantation of boron is a promising technique for the preparation of p-type emitters in n-type solar cells, e.g. for passivated emitter and rear, totally doped (PERT) cells. Although fully ion-implanted high efficiency solar cells have been reported recently, annealing of crystal defects resulting from B implantation is still challenging. We present structural investigations of implant-induced crystal defects after ion implantation of B on randomly textured Si(100) and subsequent annealing. We find that the resulting defect distribution after annealing for 20 min at 900 °C is strongly affected by the surface morphology. Ion implantation of 2·1015 cm□2 B through a 20 nm thick, thermally grown screening oxide on a sample tilted by 6 ° towards <;100> results in 3 different local defect densities: (i) for those sides of the pyramids which are tilted into the ion beam, (ii) for those sides which are tilted out of the beam and (iii) for the valleys in between the pyramids. This difference in defect density is mirrored by the effective local ion doses as obtained from process simulations. After annealing for 20 min at 1050 °C defects are observed only within the valleys of the texture.