Large-scale optoelectronics integration is limited by the inability of Si to emit light efficiently1, 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 laser2 and the heterogeneous integration of direct-bandgap III–V lasers on Si3, 4, 5, 6, 7. Here, we report lasing in a direct-bandgap group IV system created by alloying Ge with Sn8 without mechanically introducing strain9, 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 action11. 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.
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