MBE blue lasers take the next stepSharp's European research wing has made continuous-wave blue laser diodes using MBE growth.
Engineers at Sharp’s research laboratory in the UK have fabricatedthe first continuous-wave InGaN-based laser diodes to be grown by MBE.
At room temperature, the Sharp team’s latest lasers emitted around 0.2 mW for three minutes before burning out.
All commercial blue-violet laser diodes are grown by MOCVDcurrently, but early last year Jon Heffernan and colleagues at SharpLaboratories Europe produced 405 nm diodes using MBE for the first time(see related story).
However, those initial devices only worked in pulsed mode and had avery high threshold current. To be used commercially, the lasers needto work continuously and at sufficient power to read data on opticaldiscs.
“This result confirms that MBE is a viable growth method for nitridelasers,” said Heffernan. “Sharp is now in the unique position of havingboth MBE and MOCVD technologies available.”
At room temperature, the Sharp team’s latest lasers emitted around0.2 mW for three minutes before burning out. The continuous-wavethreshold current was 125 mA, corresponding to a threshold currentdensity of 5.7 kAcm-2, reports the team in the June 23 issue of the journal Electronics Letters.
Heffernan and colleagues made the lasers on n-type GaN substratessupplied by Sumitomo Electric Industries. The active laser regionincluded three undoped 3 nm-thick InGaN quantum wells with 10% indiumfraction.
The lasers operated in continuous-wave mode for around threeminutes, and across the wafer there was a variation of around 6 nmabout the crucial emission wavelength of 405 nm.
Growing the lasers by MBE rather by MOCVD promises to lowermanufacturing costs by reducing the consumption of ammonia gas, whichprovides the nitrogen content in the devices.
However, Heffernan and colleagues still have a lot of developmentwork to do before the MBE method can be considered suitable for massproduction. The team will now concentrate on improving device operatingcharacteristics by optimizing p-type doping in the AlGaN claddingregion and reducing the growth temperature, which should increase thelifetime of the devices.
Significantly, the European laboratory’s parent company already usesMBE in mass production of lasers. At its Mihara fabrication facility inHiroshima, Sharp manufactures a large proportion of the world’s redlasers that are used in DVD applications.
Sharp is also part of the Blu-ray Disc Association, along withpotential blue laser manufacturers Nichia, Sony and Matsushita Electric.
