Investigations of the dynamics of the far-infrared p-Ge laser emission reveal strong periodic soliton-like intensity spikes with less than 100 ps duration. We interpret these spikes as self-mode-locking of p-Ge laser modes. The effect becomes more pronounced when a GaAs/AlGaAs/InGaAs quantum well structure on a semi-insulating GaAs substrate is inserted into the laser cavity. (C) 1998 American Institute of Physics. [S0003-6951(98)01647-7].