Holes in germanium quantum wells: spin relaxation and temperature dynamics

We use fs-pump white-light-supercontinuum probe spectroscopy with appropriate polarization configurations to investigate the hole spin and hole cooling dynamics in Germanium quantum wells in the vicinity of the Γ valley. We observe heavy hole spin flip times of up to 1.7 ps at 10, 300 fs after the excitation. Additionally, a strong, late bleaching (Δ ~10 ps) at the lower-lying energies indicates post-injection heating of the hole system. This effect is virtually independent of the surplus energies of electrons and carrier density as long as no higher bands are involved by direct or two-photon absorption. It is a direct manifestation of energy transfer from thermalizing electrons in the L valleys to the hole system. This mechanism is supported by microscopic simulations based on the semiconductor Bloch equations, clearly identifying the cooling of the hole system