20 Oct 2005
Red emission is reported from a silicon laser doped with Europium ions.
The first silicon laser to emit visible light has been reported by a research team at the University of Cincinnati , US (J. Applied Physics 98 056108). Unlike the infrared Si lasers demonstrated previously by the University of California and Intel, which both relied on the Raman effect to achieve optical gain (see related stories), the Cincinnati device uses rare-earth doping instead.
Andrew Steckl and his co-workers observed room temperature red (620 nm) emission when they optically pumped their hybrid material laser. The structure consisted of thin layers of AlGaN and Eu-doped GaN deposited by molecular beam epitaxy (MBE) on a Si substrate. It was pumped with 600 ps duration ultraviolet (337.1 nm) pulses from a nitrogen laser and started to lase at a threshold of 117 kW/cm2.
“The combination of GaN and rare earth ions makes for a very versatile optical material system, enabling emission over the entire visible range as well as quite deep into the infrared range,” Steckl told Optics.org.
“We can replace Europium with Erbium to achieve green and IR emission or Thulium for blue emission. We have previously obtained emission from all these rare earth ions incorporated in GaN LEDs on both sapphire and Si substrates.”
One of the big challenges to overcome in making the laser was combating stress due to mismatch in the lattice and the thermal expansion properties of the Si and GaN. The use of a special intermediate AlGaN buffer layer between the two helped solve the problem.
The Cincinnati team is now looking to develop an electrically pumped version of the laser. “While our results like the ones from Intel and UCLA were obtained with use of another laser for pumping, I believe that our approach has a better chance to ultimately result in an electrically-pumped “injection” laser on Si,” said Steckl. “This is of course, a very challenging goal, but the payoff could be enormous.”