injection level spectroscopy

Several authors [1] report a injection level dependency of ELYMAT measurements. The lasers used in the ELYMAT are foccused to a spot of typically 50 microns diameter and they have a typical light power of 2 mW.

The penetration depth of the red and IR lasers is 4 respectivly 14 microns and the generation density is thus very high. The minority carrier concentration in this surface near generation region can reach the magnitude of majorities and the constant lifetime aproximation of recombination centers in the Shockley-Read-Hall theory failed.

The calculation of recombination with spartial variation of lifetime is too difficult to perform in standart measurements, on the other hand, low injection needs sometimes an other measuring technique, e.g. lock-in technique.