Ji Lian

Fabrication and Characterization of High Power InGaN Blue-Violet Lasers with an Array Structure

InGaN/GaN multi-quantum-well-structure laser diodes with an array structure are successfully fabricated on sapphire substrates. The laser diode consists of four emitter stripes which share common electrodes on one laser chip. An 800-mu m-long cavity is formed by cleaving the substrate along the . orientation using laser scriber. The threshold current and voltage of the laser array diode are 2A and 10.5 V, respectively. A light output peak power of 12W under pulsed current injection at room temperature is achieved. We simulate the electric properties of GaN based laser diode in a co-planar structure and the results show that minimizing the difference of distances between the different ridges and the n-electrode and increasing the electrical conductivity of the n-type GaN are two effective ways to improve the uniformity of carrier distribution in emitter stripes. Two pairs of emitters on a chip are arranged to be located near the two n-electrode pads on the left and right sides, and the four stripe emitters can laser together. The laser diode shows two sharp peaks of light output at 408 and 409 nm above the threshold current. The full widths at half maximum for the parallel and perpendicular far field patterns are 8 degrees and 32 degrees, respectively.

0.6-eV bandgap In0.69Ga0.31As thermophotovoltaic devices with compositionally undulating step-graded InAsyP1−ybuffers

Single-junction, lattice-mismatched In0.69Ga0.31As thermophotovoltaic (TPV) devices each with abandgap of 0.6 eV are grown on InP substrate by metal—organic chemical vapour deposition (MOCVD). Compositionally undulating step-graded InAsyP1−y buffer layers with a lattice mismatch of ~1.2% are used to mitigate the effect of lattice mismatch between the device layers and the InP substrate. With an optimized buffer thickness, the In0.69Ga0.31As active layers grown on the buffer display a high crystal quality with no measurable tetragonal distortion. High-performance single-junction devices are demonstrated, with an open-circuit voltage of 0.215 V and a photovoltaic conversion efficiency of 6.9% at a short-circuit current density of 47.6 mA/cm2, which are measured underthe standard solar simulator of air mass 1.5-global (AM 1.5 G).

Continuous-Wave Operation of GaN Based Multi-Quantum-Well Laser Diode at Room Temperature

Room-temperature operation of cw GaN based multi-quantum-well laser diodes (LDs) is demonstrated. The LD structure is grown on a sapphire (0001) substrate by metalorganic chemical vapour deposition. A 2.5 mu m x 800 mu m ridge waveguide structure is fabricated. The electrical and optical characteristics of the laser diode under direct current injection at room temperature are investigated. The threshold current and voltage of the LD under cw operation are 110mA and 10.5V, respectively. Thermal induced series resistance decrease and emission wavelength red-shift are observed as the injection current is increased. The full width at half maximum for the parallel and perpendicular far field pattern (FFP) are 12 degrees and 32 degrees, respectively.

Room-Temperature Continuous-Wave Operation of InGaN-Based Blue-Violet Laser Diodes with a Lifetime of 15.6 Hours

We report our recent progress of investigations on InGaN-based blue-violet laser diodes (LDs). The room-temperature (RT) cw operation lifetime of LDs has extended to longer than 15.6 h. The LD structure was grown on a c-plane free-standing (FS) GaN substrate by metal organic chemical vapor deposition (MOCVD). The typical threshold current and voltage of LD under RT cw operation are 78 mA and 6.8 V, respectively. The experimental analysis of degradation of LD performances suggests that after aging treatment, the increase of series resistance and threshold current can be mainly attributed to the deterioration of p-type ohmic contact and the decrease of internal quantum efficiency of multiple quantum well (MQW), respectively.