We report the observation of an abnormal photoluminescent (PL) spectrum from a HeCd laser pumped InGaN multiple
quantum well (MQW) vertical cavity. The device is fabricated using standard MOCVD deposition on a (0001)-oriented
sapphire substrate. The layer structures are: 10nm nucleation layer, a 4um bulk GaN layer, InGaN MQWs, and a final
200nm GaN cap layer. The InGaN MQWs consist of 10 pairs of 5 nm GaN barrier and 3 nm In<sub>0.1</sub>Ga<sub>0.9</sub>N well. The peak
emission of the as-grown MQWs sample was ~420nm. A dielectric distributed Bragg reflectors (DBR) were then coated
on the top layer, followed by a laser lift off from sapphire substrate, and subsequently another DBR coated on the bulk
GaN bottom surface. The cavity has a quality factor of ~520 from 400-490nm. The device was pumped by a focused CW
HeCd laser from the bulk GaN side. When the laser is focused onto the InGaN MQWs, a photoluminescent spectrum
centered at the designed MQW wavelength was observed as expected. However, when the focused position was moved
toward the bulk GaN region, an additional abnormal PL peak around 460nm was observed. This is far outside the
designed MQW wavelength.
1.27 μm InGaAs:Sb-GaAs-GaAsP vertical cavity surface emitting lasers (VCSELs) were grown by metalorganic chemical vapor deposition (MOCVD) and exhibited excellent performance and temperature stability. The threshold current changes from 1.8 to 1.1 mA and the slope efficiency falls less than ~35% as the temperature raised from room temperature to 70oC. With a bias current of only 5mA, the 3dB modulation frequency response was measured to be 8.36 GHz, which is appropriate for 10 Gb/s operation. The maximal bandwidth is measured to be 10.7 GHz with modulation current efficiency factor (MCEF) of ~ 5.25 GHz/(mA)1/2. These VCSELs also demonstrate high-speed modulation up to 10 Gb/s from 25°C to 70°C.
Large-area (1000×1000 μm<sup>2</sup>) p-side down InGaN light-emitting diodes (LEDs) have been fabricated by laser lift-off (LLO) technique. The p-side down LEDs with different geometric patterns of n-electrode were fabricated to investigate electrode pattern-dependent optical characteristics. Current crowding effect was first observed in in the p-side down InGaN LLO-LEDs. The LEDs with well designed n-electrode shows a uniform distribution of light-emitting pattern and higher out put power due to uniform current spreading and minimization of thermal effect. The output power saturation induced by current crowding in the LEDs with simplest geometric n-electrode was demonstrated. In absent of transparent contact layer for current spreading, the n-electrode pattern has remarkable influence on the current distribution and consequently the light output power of the large-area p-side down LEDs.