Two-dimensional numerical simulation of boron diffusion for pyramidally textured silicon

Abstract

Multidimensional numerical simulation of boron diffusion is of great relevance for the improvement of industrial n-type crystalline silicon wafer solar cells. However, surface passivation of boron diffused area is typically studied in one dimension on planar lifetime samples. This approach neglects the effects of the solar cell pyramidal texture on the boron doping process and resulting doping profile. In this work, we present a theoretical study using a two-dimensional surface morphology for pyramidally textured samples. The boron diffusivity and segregation coefficient between oxide and silicon in simulation are determined by reproducing measured one-dimensional boron depth profiles prepared using different boron diffusion recipes on planar samples. The established parameters are subsequently used to simulate the boron diffusion process on textured samples. The simulated junction depth is found to agree quantitatively well with electron beam induced current measurements. Finally, chemical passivation on planar and textured samples is compared in device simulation. Particularly, a two-dimensional approach is adopted for textured samples to evaluate chemical passivation. The intrinsic emitter saturation current density, which is only related to Auger and radiative recombination, is also simulated for both planar and textured samples. The differences between planar and textured samples are discussed.

“Zero-charge” SiO2/Al2O3 stacks for the simultaneous passivation of n+ and p+ doped silicon surfaces by atomic layer deposition

“…1) using a WEP wafer profiler CVP21 table-top unit. Note, that the doping profile of the boron-doped samples can be affected by the texture of the surface, and a heavier doping level can be expected at the pyramid tips [37]. The sheet resistance and the homogeneity of the doped regions were measured using a Signatone four-point probe, in combination with a Keithley 2400 Source Measurement Unit.…”

Dielectric surface passivation for silicon solar cells: A review

“…It is actually found that the fundamental recombination rate at, e.g. Si‐Al 2 O 3 surfaces, is independent of the surface dopant density .…”

The interplay between emitter conformality and field‐effect passivation in pyramid structured silicon solar devices

“…In the presented case, the intrinsic Auger recombination amounts to an emitter dark saturation current density ( J 0e ) of below 5 fA/cm 2 from theoretical calculations 37 . However, once the peak dopant concentration is raised to ~5 × 10 19 cm −3 and close to the boron solubility limit, 38 Auger recombination in the emitter bulk then begins to dominate 39 . Moreover, reprocessing the heterojunction emitter samples for producing their homojunction counterparts increases the likelihood of introducing scratch marks on wafer surfaces to serve as effective recombination sites.…”

“…The diffusion process for a boron‐doped (p ++ ) emitter was emulated by adopting the approach outlined in reference 39 . A p ++ ‐doped BSG layer was defined on a c‐Si surface for mimicking the predeposition step.…”