Effective lifetime measurements on phosphorus emitters prepared with planar diffusion sources

In this work we present a study of phosphorus doped emitters using solid diffusion sources. This doping technique has a special interest in high efficiency solar cell fabrication because it can reach good uniformity and repeatability between samples, allowing uniform low doping emitter profiles (sheet resistance R_sh/100Omegasq). Pre-deposition in the temperature range from 815degC to 900degC yields emitter sheet resistance from 30 to 900 Omega/sq with a in-wafer deviation of about 6% on 4" wafers. We determine the reverse saturation current density, J_oe, of our emitters by measuring the injection level dependence of effective lifetime using the quasi steady-state photoconductance (QSS-PC) method. J_oe in phosphorus glass passivated emitters after the pre-deposition step is in the range of 160 to 400 fA/cm2. From data fitting of dependence of Joe with sheet resistance using PC-ID, the empiric fundamental surface recombination velocity is determined to be S_o= 175 cm/s for the phosphorus glass passivated emitter surface