Lifetime of excess electron–hole pairs measured with white noise performance of the photocurrent

A modified method to measure the lifetime of the excess electron–hole pairs generated by laser beams is proposed. Under the applied bias, excess carriers pass through the sample within the transit time and form the photocurrent Ip. The related white-noise component of the photocurrent can be written as 4egIp, where g is the ratio of the lifetime over the transit time. The lifetime can then be obtained by determining g from the white noise performance. Since the transit time can be adjusted with the applied biases and the sample length, the measured lifetime may be as small as 100 ns with the measurement system even having the analytic frequency range of 10 kHz only. A GaAs sample grown by molecular beam epitaxy is taken as an example to measure the excess carrier’s lifetime. It is concluded from the experiments that the lifetime of excess carriers in our sample is primarily caused by the indirect recombination via the deep trap centers within the band gap. The nonradiative lifetime is not really a constan...