R. Winn Hardin
PALO ALTO, Calif. -- A small -- a very small -- spot of color here and there is behind Xerox's development of a blue laser diode.
Xerox hopes to use the nitride-based semiconductor technology to create a new line of high-resolution printers. Like optical storage disks, laser printers make use of smaller wavelengths to cram more data into a given area.
Laser printers use a charged photoreceptor to convert laser light into hard copies. A blue laser will allow Xerox to draw a more detailed picture on the photoreceptor, according to Xerox researcher David Bour.
Xerox's contribution to the quest for a blue diode laser comes in a little longer than most -- about 427 nm. Several hurdles remain, however, before the group can claim commercial success. Photo courtesy of Xerox Corp. and Brian Tramontana.
Bour and his colleagues created the blue semiconductor laser using metal-
organic chemical vapor deposition to grow 10 GaInNi quantum wells on a sapphire substrate. The high bandgap material AlGaNi surrounds the active region, providing cladding for the semiconductor laser cavity. "The big thing was learning to grow and process the nitride materials," Bour said. "Metal-organic chemical vapor deposition was used because it's the same technique used with red lasers and many IR [semiconductor] lasers."
Bour's group chose chemically assisted ion beam etching to create the mirrors that act as bookends to the laser cavity.
Xerox's approach has delivered blue light centered around 427 nm, a longer wavelength than lasers developed by blue laser guru Shuji Nakamura of Nichia Chemical Industries Inc. of Japan, and Cree Research Inc. of Durham, N.C. "That may not be ideal for optical storage, where a shorter wavelength is desirable," Bour added. "But it could be good for printers because it depends on the [wavelengths] of photoreceptors available." He declined to comment on the target wavelengths of Xerox's photoreceptors.
Making it commercial
Before Xerox stands the task of lowering the laser threshold. Bour estimates that dividing the 25-kA/cm2 threshold by about 10 should permit the continuous wave (CW) operation that is crucial to successful commercial products. Nakamura has succeeded in delivering CW output at 1.5 kA/cm2, with a projected lifetime of 10,000 hours.
Xerox is the third US company and eighth in the world to develop nitride blue laser semiconductor technology. Last month's announcement was the result of two years of development, Bour said, and marks a significant step toward using nitride lasers for printing applications.