Characterizations of direct gap emission from epi-Ge through both optical and electrical pumping were studied for the application of Si compatible light sources such as on-chip optical interconnect. In-situ doping technique with PH3 during the epi-Ge growth was first applied to achieve high n-type doping concentrations. Photoluminescence (PL) measurements show that the direct band emission of Ge increases with higher doping concentration. This confirms that the Ge direct radiative recombination efficiency can be improved by band filling of electrons. A Ge n+/p light emitting diode (LED) on a Si substrate was then fabricated to study the electroluminescence (EL) properties related to the band filling. Direct band gap EL at 1.6 μm was also obtained from this Ge LED. Unlike ordinary electrically pumped devices, this LED shows a superlinear luminescence enhancement at high current. Thermal enhancement effects observed in temperature dependent EL spectra show the capability of this device to be operated at room temperature or above.