The University of Arkansas is claiming a first – an electrically-pumped germanium-tin laser grown monolithically on silicon.

Uof-Arkansas-laser GeSn

Electrical pumping is a big deal – many proof-of-concept semiconductor lasers, including an earlier version of this device, have to have their operating energy delivered optically through other lasers. However, the laser still requires cryogenic cooling to function.

GeSn is of interest because with enough tin (>8%) it becomes a direct bandgap material – suitable for laser use – and its lattice is compatible with growth on a silicon substrate – including with CMOS.

In this case, it is ridge waveguide laser with a GeSn/SiGeSn double heterostructure (see diagram).

Its layers are:

• (Si-Ge)Sn p+ cap with electrical  contact
• (Si-Ge)Sn p-type cap
• GeSn un-doped active layer
• GeSn n+ buffer with electrical  contact
• Ge n+ buffer
• Si substrate

“Our results are a major advance for group-IV-based lasers,” said Arkansas engineer professor Shui-Qing ‘Fisher’ Yu. “They could serve as the  route for laser integration on silicon and a step toward improving circuits for electronics devices.”

The laser was cooled to 100K, and pulse-tested. Emission is a few mW at ~2.3μm.

“The results indicate advances for group-IV-based lasers, which could serve as a promising route for laser integration on Si,” according to the paper ‘Electrically injected GeSn lasers on Si operating up to 100 K‘, which describes the work in Optica, and is available in full without charge.

The University of Arkansas worked with Arizona State University, the University of Massachusetts Boston, Dartmouth College New Hampshire, Wilkes University Pennsylvania and semiconductor equipment maker Arktonics. Sponsorship came from the US Air Force Office of Scientific Research.