Study of Carrier Statistics in Uniaxially Strained Ge for a Low-Threshold Ge Laser

In this paper, we present a comprehensive study of carrier statistics in germanium with high uniaxial strain along the [100] direction. Several types of PL experiments were conducted to investigate polarization-, temperature- and excitation-dependent carrier statistics in germanium under various amounts of uniaxial strain. With the ability to clearly resolve multiple photoluminescence peaks originating from strain-induced valence band splitting, we experimentally observed strongly polarized light emission from direct band gap transitions. Our experiments also confirm that uniaxial strain increases the hole population in the highest valence band as well as the electron population in the direct conduction band. Based upon our experimental results, we present theoretical modeling showing that the lasing threshold of a germanium laser can be reduced by >100× with 2.5% strain.