Direct determination of ultrafast intersubband hole relaxation times in voltage biased SiGe quantum wells by a density matrix interpretation of femtosecond resolved photocurrent experiments

P Rauter, T Fromherz, N Q Vinh, B N Murdin, J P Phillips, C R Pidgeon, L Diehl, G Dehlinger, D Grützmacher, Ming Zhao, Wei-Xin Ni, G Bauer
2007 New Journal of Physics  
We report the quantitative and direct determination of hole intersubband relaxation times in a voltage biased SiGe heterostructure using density matrix calculations applied to a four-level system in order to interpret photocurrent (PC) pump-pump experiments. One consistent set of parameters allows the simulation of two kinds of experiments, namely pump-pump photocurrent experiments at a free electron laser (wavelength 7.9 µm) and the laser-power dependence of the PC signal. This strongly
more » ... his strongly confirms the high reliability of these parameter values, of which the most interesting in respect to Si based quantum cascade laser development is the extracted heavy-hole relaxation time. The simulations show that this relaxation time directly determines the experimentally observed decay of the pump-pump photocurrent signal as a function of the delay time. For a heavy hole intersubband spacing of 160 meV, a value of 550 fs was obtained. The experimental method was further applied to determine the LH1-HH1 relaxation time of a second sample with a transition energy below the optical phonon energy. The observed relaxation time of 16 ps
doi:10.1088/1367-2630/9/5/128 fatcat:hu2o2fplmbes5kae3avd2jlhdu