|A schematic (left) shows a gallium arsenide/aluminum gallium arsenide (GaAs/AlGaAs) quantum-dot laser monolithically integrated on a silicon substrate. An optical micrograph (right) details the quantum dots. (Image: DARPA)|
Scientists in the Electronic-Photonic Heterogeneous Integration (E-PHI) program run by the U.S. Defense Advanced Research Projects Agency (DARPA; Washington, DC) have deposited successive layers of indium arsenide material directly on silicon (Si) wafers to form quantum-dot (QD) based lasers that can directly become part of photonic circuits. The development was achieved by researchers at the University of California, Santa Barbara (UCSB). The research was published in a recent issue of Applied Physics Letters.
As is well-known by readers of Laser Focus World, the non-gain portions (waveguides, splitters, and so on) in Si-based photonic circuits are straightfroward to make, and can be fabricated from within the conventional CMOS process. However, on-chip light sources are a different story, because Si itself is very difficult to make into a laser.
Conventional approaches include separately fabricating III-V semiconductor lasers, then precisely positioning and bonding them onto Si wafers -- a time-consuming and finicky process. The new approach eliminates the need for bonding and thus has application in numerous military and civilian electronics where size, weight, power, and packaging/assembly costs are critical.
The UCSB team overcame lattice mismatch of indium arsenide materials with Si, showing that lasers grown on silicon performed comparably to those grown on their native substrate. These results serve as a foundation for the development of other photonic components such as optical amplifiers, modulators, and detectors.
DARPA started the E-PHI program in 2011 with a goal of integrating chip-scale photonic microsystems with high-speed electronics directly on a single silicon microchip. Defense systems, such as radar, communications, imaging, and sensing payloads, which rely on a wide variety of microsystems devices, can all benefit from a move to photonic circuits that can be fabricated without the need for wafer bonding.
Major teams currently participating in E-PHI are led by the following organizations:
--Aurrion, Inc. (Goleta, CA)
--Massachusetts Institute of Technology (Cambridge, MA)
--University of California, Berkeley (Berkeley, CA)
--University of California, San Diego (La Jolla, CA)