Impact of c-Si Surface Passivating Layer Thickness on n+ Laser-Doped Contacts Based on Silicon Carbide Films

Abstract

Laser processing of doped dielectric films has been proposed as a feasible alternative avoiding energy-consuming conventional dopant diffusions. In this approach, silicon surface passivation is usually obtained by means of a thin passivating layer deposited onto the silicon surface following what is done in heterojunction devices. However, laser doping from dielectric films relaxes the tradeoff between surface passivation and carrier transport and, as a consequence, thicker passivating films can be used improving the passivation. In particular, we focus on phosphorus-doped dielectric film stacks with a first thin intrinsic amorphous silicon carbide layer, which is responsible for surface passivation. In this paper, we explore the effect of the thickness of this passivating layer on crystalline silicon (c-Si) surface passivation and on the quality of the n+ contact created by laser processing. Surface recombination velocities for the full dielectric stack of 6 cm/s are measured when the layer thickness is increased to 22 nm while simultaneously keeping specific contact resistivity below 1 mΩ·cm 2 and surface recombination at the contact to values in the 2500–2850 cm/s range. Then, the introduction of thicker passivating films results in a better c-Si surface passivation with similar contact properties that could improve the efficiency potential of solar cells.