Figure 3
From: Optically reconfigurable polarized emission in Germanium
Modelling of the power-dependent PL polarization. Circular polarization degree of the direct gap PL measured as a function of the excitation power density in two n-doped Ge samples having the same doping content of 8.3 × 1016 cm−3 (red squares and blue circles). The estimated excess carrier density corresponding to the pump power is also shown (see Supplementary Note 2). The black dashed line is the result of the kinetic model obtained by considering the excitation and recombination dynamics of spin polarized carriers schematically shown in the inset. Under circularly polarized laser excitation, spin up electrons (G↑) are photoexcited close to the Γ valley edge (Γ<) from the split-off (SO) valence band state, while spin down electrons (G↓) are promoted from the heavy (HH) and light hole (LH) states to higher energies (Γ>). The indirect band gap nature of Ge favours scattering of electrons out of the zone centre towards the X valleys and the absolute L minima. However, increasing the excitation power density (П), it is possible to strengthen the X-Γ backwards scattering, thus enhancing the spin down electron population contributing to the direct gap polarized PL (R). The different arrows thicknesses suggest the different efficiencies of the processes.
