Semiconductor lasers have become the backbone of modern optical telecommunications and are also used in an increasing number of applications in engineering, biology, chemistry and medicine. Historically, semiconductor laser device technology took off following the demonstration of electrical injection in double heterostructure diodes in the late 1960s. In these devices, confinement of electrically injected electron hole pairs inside a narrow optical gain region resulted in recombination rates that were sufficiently high to allow continuous-wave operation at room temperature. Subsequent advances in the epitaxial growth of low-dimensional semiconductor heterostructures and improved device geometries enabled greater control over the electronic and photonic confinement on a nanometre scale, allowing for even more dramatic reductions in the laser threshold current. However, the basic principle of lasing in semiconductor lasers namely creating a population inversion to produce lasing action under electrical injection in semiconductors has remained unchanged for decades.

The report of an electrically pumped polariton laser that operates at room temperature and relies on an inversionless lasing scheme holds promise for realizing a new breed of very low threshold semiconductor lasers.

From: Pavlos G. Savvidis “Optoelectronics: A practical polariton laser“, Nature Photonics 8, 588-589 (2014).