Selective Boron Emitters Using Laser-Induced Forward Transfer Versus Laser Doping From Borosilicate Glass

Although highly doped boron selective emitters (SEs) can be formed by using laser doping (LD) from the borosilicate glass remaining after boron tribromide tube diffusion, the dopant concentration is limited. This limitation can be overcome by using a laser-induced forward transfer (DLIFT) approach. In this work, SEs formed by DLIFT and LD are compared to a homogenous tube diffusion (Diff) emitter. We investigated the correlation of the emitter saturation current density (j
_0e
) and the specific contact resistance (ρ
_c
) with the sheet resistance (R
_sheet
) and the laser pulse energy density (E
_p,d
). For passivated emitters, j
_0e
of DLIFT and LD emitters was around ten times higher than j
_0e
of Diff emitters. For metallized emitters, simulated j
_0e
of DLIFT emitters was lower than j
_0e
of LD and Diff emitters for R
_sheet
glt; 40.0 Ω/sq. Moreover, we show how j
_0e
can be further reduced by increasing the surface dopant concentration of the boron emitter and by reducing the laser-induced defects in the silicon crystal. Additionally, the metallization of DLIFT emitters with aluminum-silver paste by screen printing provided low contact resistances between metal and silicon (ρ
_c
<; 1.0 mΩ · cm
²
). Thus, p-type emitters can be optimized by forming an SE with the highly doped boron regions achieved by DLIFT under the screen-printed metallization.