Lasing in direct-bandgap GeSn alloy grown on Si

Large-scale optoelectronics integration is limited by the inability of Si to emit light efficiently(1), because Si and the chemically well-matched Ge are indirect-bandgap semiconductors. To overcome this drawback, several routes have been pursued, such as the all-optical Si Raman laser(2) and the heterogeneous integration of direct-bandgap III-V lasers on Si3-7. Here, we report lasing in a direct-bandgap group IV system created by alloying Ge with Sn-8 without mechanically introducing strain(9,10). Strong enhancement of photoluminescence emerging from the direct transition with decreasing temperature is the signature of a fundamental direct-bandgap semiconductor. For T <= 90 K, the observation of a threshold in emitted intensity with increasing incident optical power, together with strong linewidth narrowing and a consistent longitudinal cavity mode pattern, highlight unambiguous laser action(11). Direct-bandgap group IV materials may thus represent a pathway towards the monolithic integration of Si-photonic circuitry and complementary metal-oxide-semiconductor (CMOS) technology.