Ultra-low lasing threshold achieved in electrically injected lateral InGaN/ GaN nanowires
Lasers have transformed many aspects of modern life – from surgery & forensics to electronic storage & printing. Even high-speed internet travels on laser light through fiber-optic cables. Then again, lasers can do much more. With a laser that fits inside an integrated circuit (IC) chip, on-chip optical circuits can give us faster & more power-efficient ICs and sensors. Recent work by Prof. Saha and his team on InGaN/ GaN nanowire lasers takes us closer to that possibility.
So far, other research groups have demonstrated lasers using vertically standing nanowires. They generally need to optically pump them to start lasing. To make optical ICs viable, it helps to have nanowire lasers that work when horizontally arranged and electrically pumped. In this work, the team was successful in activating their lateral nanowires electrically at a current density as low as 28.6 A/cm2. This was possible due the unique structure of their device – their nanowire laser had nano-sized mirrors distributed at its ends to enhance its performance.
While fabricating this structure, triangularly-shaped nanowires were first wet etched out from a stack of indium-gallium-nitride (InGaN) and gallium nitride (GaN) quantum wells. Thereafter, nano-sized mirrors of polymethyl methacrylate (PMMA) were added to their ends via e-beam lithography. Optical feedback from these distributed mirrors enabled lasing at very low threshold currents. Wavelength of the laser light was 433.8 nanometres and its line width was 5 angstroms. Their results provide a way forward for nano-sized lasers to be used in optoelectronic circuits.
Work funded/supported by: Dept. of Science & Technology (DST) of Government of India (GoI).
Published paper: D. Banerjee, K. Takhar, S. Sankaranarayanan, P. Upadhyay, R. Ruia, S. Chouksey, D. Khachariya, S. Ganguly and D. Saha, “Electrically injected ultra-low threshold room temperature InGaN/GaN-based lateral triangular nanowire laser”, Applied Physics Letters, vol 107, pg. 10118 (2015).