Hole response time and the experimental test of the Einstein relation

The concept for the experimental test of the Einstein relation for non-Gaussian transport as suggested by Q. Gu et al. [Phys. Rev. Lett. 76, 3196 (1996)] is critically examined. It is shown that the photocurrent response time, which is employed to set the time scale for comparing drift and diffusion of excess holes! is instead related to the decay of the excess electron population and therefore not suitable for a correct use in the experimental test in a general manner. It is demonstrated that the minority hole population decay time, as needed for the experimental test, is found to be typically larger than the decay time for majority electrons. A reevaluation of the experimental data with this insight provides improved evidence that the Einstein relation holds under the above conditions of non-Gaussian hole transport.