The transient inter-valence-band absorption in p-type germanium investigated with picosecond excitation and probe pulses in the mid-infrared gives direct information on the time evolution of hot-hole distributions. Spectrally and temporally resolved measurements are reported for different carrier concentrations between ${10}^{16}$ and ${10}^{17}$ ${\mathrm{cm}}^{\mathrm{-}3}$ and for lattice temperatures from 30 to 300 K. A fast bleaching of the heavy-hole-to-light-hole transition is followed by an absorption increase after excitation at wavelengths around 10 μm. The strength and the picosecond decay times of the two contributions depend on the initial carrier temperature, the pumping intensity, and the spectral position of the probe pulses. Subpicosecond carrier-carrier and inter-valence-band scattering lead to the rapid formation of an equilibrium distribution of hot heavy holes which cools predominantly by emission of optical phonons on a time scale of several tens of picoseconds. Theoretical simulations of carrier cooling give a coupling constant of the optical deformation potential of ${\mathit{D}}_0$=6.3×${10}^8$ eV/cm.

• Received 21 August 1991

DOI:https://doi.org/10.1103/PhysRevB.45.8378