D.W. Treat

Strained Ga/sub x/In/sub 1-x/P/(AlGa)/sub 0.5/In/sub 0.5/P heterostructures and quantum-well laser diodes

The properties of (AlGa)/sub 0.5/In/sub 0.5/P, strained Ga/sub x/In/sub 1-x/P/(AlGa)/sub 0.5/In/sub 0.5/P heterostructures, and single quantum well (QW) laser diodes with Al/sub 0.5/In/sub 0.5/P cladding layers, prepared by low pressure organometallic vapor phase epitaxy, are described. The influence of biaxial strain upon the relative positions of the valence band edges are examined by analyzing the polarized spontaneous emission. Laser diodes with wavelength 620 >

Drift leakage current in AlGaInP quantum-well lasers

The temperature dependence of threshold current and quantum efficiency for Ga/sub x/In/sub 1-x/P (x=0.4, 0.6; lambda =680, 633 nm) single 80-AA quantum-well lasers is compared and analyzed using a model for the electron leakage current. This model fits the experimental data well, correctly describing the rapid increase in threshold and drop in quantum efficiency as temperature increases. Also, it indicates that the drift (rather than diffusion) component of the electron leakage current, is dominant, because of the poor p-type conductivity in AlGaInP. >

Continuous-wave InGaN multiple-quantum-well laser diodes on copper substrates

Continuous-wave (cw) indium-gallium nitride multiple-quantum-well laser diodes (LDs) were transferred from sapphire onto copper substrates using a two-step laser lift-off process. Reduced threshold currents and increased differential quantum efficiencies were measured for LDs on Cu due to a 50% reduction of the thermal impedance. Light output for LDs on Cu was three times greater than comparable LDs on sapphire with a maximum output of 30 mW. CW operation was possible up to heatsink temperatures of 90 °C for LDs on Cu.

Near-bandedge cathodoluminescence of an AlN homoepitaxial film

Cathodoluminescence experiments were performed on a high-quality AlN epitaxial film grown by organometallic vapor phase epitaxy on a large single crystal AlN substrate. The low-temperature near-bandedge spectra clearly show six very narrow lines. The thermal quenching behavior of these emission lines provides insight on how to assign them to free and bound exciton recombination processes. The binding energy for the free-exciton-A in AlN was found to be nearly twice that in GaN. The observation of the free-exciton-A first excited state permitted us to estimate its reduced effective mass and, by using recent reported values for the hole effective mass in Mg-doped AlN, the electron effective mass in AlN has been deduced.

Planar laterally oxidized vertical-cavity lasers for low-threshold high-density top-surface-emitting arrays

We introduce a novel device architecture that enables the fabrication of low threshold high density vertical-cavity surface-emitting laser (VCSEL) arrays. Our structure relies on a group of small via holes to access a buried AlGaAs layer for lateral oxidation. In contrast to the conventional method of exposing mesa sidewalls through etched pillars, this technique provides our VCSELs with the benefits of oxide confinement without sacrificing wafer planarity. Maintaining wafer planarity is essential for the easy fabrication and contacting of densely packed devices. The devices operate at 827 nm, with a minimum threshold current of 200 /spl mu/A, and a maximum output power of 3.15 mW.

Influence of microstructure on the carrier concentration of Mg-doped GaN films

Room-temperature Hall effect measurements of (0001) Mg-doped GaN films grown on sapphire substrates by metalorganic chemical vapor deposition show a reduction in hole concentration for Mg concentrations greater than 1020 cm−3. A combination of secondary ion mass spectrometry and transmission electron microscopy indicates a steadily increasing Mg incorporation during growth and the formation of inversion domains at these high concentrations. We discuss mechanisms that could give rise to a reduction of the hole concentration at high Mg doping levels.

Continuous-wave operation of ultraviolet InGaN/InAlGaN multiple-quantum-well laser diodes

We demonstrate ultraviolet InGaN/InAlGaN multiple-quantum-well laser diodes operating under continuous-wave (cw) conditions. The laser diodes were grown on sapphire substrates by metalorganic chemical vapor deposition. Under pulsed bias conditions, we have achieved threshold current densities as low as 5 kA/cm2 for laser diodes with emission wavelengths between 368 nm and 378 nm and have demonstrated lasing at 363.2 nm at room temperature, the shortest wavelength yet reported for a semiconductor laser diode. The cw operation up to a heat sink temperature of 40 °C was demonstrated on a series of narrow ridge-waveguide devices processed with chemically assisted ion beam etched mirrors and high reflective coating on both facets. The shortest wavelength emission under cw operation conditions was 373.5 nm with output powers of more than 1 mW.

Ultraviolet AlGaN multiple-quantum-well laser diodes

We demonstrate ultraviolet emission from current-injection AlGaN multiple-quantum-well laser diodes grown on sapphire substrates by metalorganic chemical vapor deposition. Lasing was obtained in gain-guided laser diode test structures with uncoated facets and cavity length ranging from 400 to 1500 μm. Under pulsed bias conditions, threshold current densities as low as 23 kA/cm2 have been achieved for laser diodes with emission wavelengths between 359.7 and 361.6 nm. The maximum output power was 45 mW per facet with differential quantum efficiencies of 1.3%.

Performance and degradation of continuous-wave InGaN multiple-quantum-well laser diodes on epitaxially laterally overgrown GaN substrates

The performance and degradation characteristics of continuous-wave (cw) InGaN multiple-quantum-well laser diodes are reported. A cw threshold current as low as 62 mA was obtained for ridge-waveguide laser diodes on epitaxially laterally overgrown GaN on sapphire substrates grown by metalorganic chemical vapor deposition. Transmission electron microscopy reveals a defect density <5×107 cm−2 in the active region. The emission wavelength was near 400 nm with output powers greater than 20 mW per facet. Under cw conditions, laser oscillation was observed up to 70 °C. The room-temperature cw operation lifetimes, measured at a constant output power of 2 mW, exceeded 15 h. From the temperature dependence of the laser diode lifetimes, an activation energy of 0.50 eV±0.05 eV was determined.

Indium tin oxide transparent electrodes for broad-area top-emitting vertical-cavity lasers fabricated using a single lithography step

We report for the first time top-emitting buried oxide vertical cavity lasers using transparent indium tin oxide electrodes. Our process enables broad-area InAlGaAs VCSELs to be fabricated in a single lithography step, thus allowing the fast turn-around time necessary for evaluating VCSEL epitaxial materials. The ITO contacts attain a peak transmission of 96%, a specific contact resistance of 10/sup -5/ /spl Omega//spl middot/cm/sup 2/, and a sheet resistivity of 2.5/spl times/10/sup -4/ /spl Omega//spl middot/cm. Under room temperature CW pumping, the devices exhibit a minimum threshold current density of 1.2 kA/cm/sup 2/ at a wavelength of 801 mm, and have a maximum light output power of 5.2 mW.