VCSEL Brings Advantages of IC Fabrication to Optoelectronic Markets

As IC fabrication companies have long understood, the incremental cost of processing a wafer doesn't change much with the number of devices on the wafer. The more devices you can squeeze onto a single piece of silicon (or GaAs), the less each one costs. Emcore Corporation's new Gigalase 850 nm vertical cavity surface emitting laser (VCSEL) applies this lesson to optoelectronic devices. Announced at this week's Optical Fiber Communication Conference in San Jose, Calif., the Gigalase is the first commercially available 850 nm VCSEL designed specifically for merchant optical communications.

Conventional laser diodes emit their light horizontally, from the edge of the die (See Figure). Very thin layers are deposited to make horizontal light emitting structures, then the manufacturer cleaves the wafer into small pieces for packaging. Cleaving damages the region near the fracture surface, reducing yield to only 1000 lasers per 3" GaAs wafer.

VCSELs emit light from the die surface instead. Bill Leasure, vice president of marketing and sales at Emcore's MODE division, told Semiconductor Online that the new VCSEL achieves more than 10x greater yield than edge-emitting designs, with up to 20,000 functioning lasers per 3" GaAs wafer. Manufacturing costs shrink dramatically. Testing costs shrink, too, since the lasers can be tested in place, before dicing the wafer. Bad die need not be packaged, and problems are more easily traced to the source.

The VCSEL technology, originally developed at Sandia National Laboratory in Albuquerque, NM, relies on in situ monitoring during epitaxial growth. The light-emitting quantum wells require feature sizes on the order of a few Å achieved with electron beam lithography and what Leasure described as "many many mask layers."

The Gigalase is intended for fiber optic communications, and allows gigabit/second transceiver performance. Surface emission enforces fewer packaging constraints, however, so other novel applications may be possible.

For more information:
Bill Leasure, MODE
5601-C Midway Park NE
Albuquerque, NM 87109
Tel: 505-343-1111; Fax: 505-343-8300.

By Katherine Derbyshire