Hot carriers relaxation in highly excited polar semiconductors: Hot phonons versus phonon–plasmon coupling

Abstract

We present a study of the photo-excited charge carriers relaxation dynamics in polar semiconductors comparing calculations to pump probe experiments. Hot carrier densities in the 1018cm-3 range can easily be photo-generated using moderately intense optical excitations. This can lead to known phenomena, namely, hot phonon populations and the coupling of polar optical phonons with plasmon modes. However, these two phenomena can affect the hot carriers relaxation and have never been examined together. This is a problem for the theoretical study of future Hot Carrier Solar Cells, where the conditions allow both of these phenomena to occur. The charge carriers dynamics and the coupling of polar optical phonons with plasmon modes are treated by a Full Band Ensemble Monte Carlo simulation code featuring a self-consistent dielectric function. To take into consideration hot phonon populations and the subsequent phonon bottleneck for the carriers relaxation, the charge carriers simulation code is coupled to a phonon dedicated Ensemble Monte Carlo code. This enables for the first time an accurate study of both the charge carriers and phonon systems dynamics, the latter being most of the time overly simplified in previous studies. The present work explores to which extent the two aforementioned phenomena affect the photo-generated charge carriers relaxation in GaAs and can be easily adapted to other polar semiconductors.