Creation of the first directly electrically pumped vertical-cavity surface-emitting laser (VCSEL) has been reported by a group of scientists at National Chiao Tung University (Hsinchu, Taiwan). Operating at the liquid-nitrogen temperature of 77 K, the continuous-wave device emits at 462 nm with a linewidth of 0.15 nm, a divergence angle of 11.7º, and a polarization ratio of 80%. Although the intensity at the emission aperture was nonuniform (looking mottled), the intensity of the laser’s focused spot appeared symmetric, with a diameter of about 3 μm.
One trick to fabricating a functional laser was creating a distributed Bragg reflector (DBR) that didn’t crack because of differing thermal-expansion coefficients; the resulting microcavity structure had one DBR of aluminum nitride/gallium nitride, and the other of tantalum pentoxide/silicon dioxide. A ten-pair indium gallium nitride/gallium nitride multiple quantum well served as the active region; the resulting cavity length was about 10.5λ. A highly transparent layer of indium tin oxide served to inject carriers into the active region without hindering the laser’s optical output. The threshold current density for a 10-μm-diameter current-injection area was about 1.8 KA/cm2. Contact Shing-Chung Wang at [email protected].