Free and bound exciton fine structures in AlN epilayers grown by low-pressure metalorganic vapor phase epitaxyCathodoluminescence 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.

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.

The temperature dependence of threshold current and quantum efficiFncy for Ga,In, -,P (x = 0.4, 0.6; 1 = 680, 633 nm) single 80 A 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 AIGaInP.

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%.

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.