First-principles study of light emission from strained germanium

Light emissions due to direct transitions in strained germanium with electron doping are studied based on first principles calculations. We found that an accuracy of the band structure is a key to improve reproducibility of experimental measurements. Combinations of carrier density, strain, and temperature necessary for lazing are discussed based on these calculations. We also found that measuring temperature dependence of spontaneous emission helps estimation whether electron injection is sufficient or not.