Review and comparison of equations relating bulk lifetime and surface recombination velocity to effective lifetime measured under flash lamp illumination

Photoconductance measurements are frequently used to determine the minority-carrier effective lifetime (τeff), from which the bulk lifetime (τb) and surface recombination velocity (S) must be extracted. The exact solution to the continuity equation is used to determine the conditions of validity for three approximate equations relating τeff to τb and S: the steady-state approximation, the transient approximation, and the widely used simple equation (1/τeff=1/τb+2S/W). We show that only the steady-state approximation matches the exact solution over the entire range of τeff, when the lamp time constant is 2.3 ms. When τeff>20 μs, all the equations give approximately the same result. However, when τeff<10 μs, only the steady-state equation is valid, while the error in the transient and simple equations may exceed 100%.