Carrier Lifetime Measurements of Monocrystalline Silicon Ingots Using Upgraded Laser E-PCD Technique

The photoconductance decay (PCD) method is a standard characterization technique for carrier lifetime characterization of silicon ingots. We analyzed the precision of the eddy current PCD technique using monochromatic light focusing on the impact of the properties of the laser excitation.The PCD measurement simulations showed that the impact of the surface recombination in the measured lifetime and the injection level is highly influenced by the wavelength and the pulse duration of the laser excitation source. Considering the time evolution of carrier profile as well, an optimal wavelength range between 1050 and 1070 nm has been found. The eddy-current detected PCD (e-PCD) measurements using the original 980 nm and a rather optimal 1064 nm laser was compared experimentally and by simulation in details. In the injection independent lifetime model, the effective lifetime approaches the bulk lifetime asymptotically within a reasonable time, and both laser source provides accurate result as experimentally confirmed. However, if carrier lifetime varies significantly with injection level, a pronounced difference between the asymptotic lifetimes recorded using the different lasers is observed. Lifetime values from the longer wavelength setup approach the saturation value of bulk lifetime even in this case. This is an additional important advantage of using the longer wavelength laser for ingot PCD measurements.Comparing the laser e-PCD results to flash lamp based PCD systems, a good correlation is found in the long lifetime regime. However, the significant discrepancies found between transient and Quasi-Steady-State (QSS) modes of the flash lamp PCD system indicate that performing the measurement