[en] We report the 300 K operation of optically pumped red-emitting lasers fabricated from InP self-assembled quantum dots embedded in In_0.5Al_0.3Ga_0.2P layers on GaAs (100) substrates grown by metalorganic chemical vapor deposition. Quantum dots grown at 650 degree C on In_0.5Al_0.3Ga_0.2P layers have a high density on the order of 10¹⁰ cm^-2 and the dominant size of individual quantum dots ranges from ∼5 to ∼10 nm for 7.5 monolayer 'equivalent growth.' These InP/In_0.5Al_0.3Ga_0.2P quantum dot heterostructures are characterized by atomic force microscopy, high-resolution transmission electron microscopy, and photoluminescence. Laser structures are prepared from wafers having two vertically stacked InP quantum dot active layers within a 100-nm-thick In_0.5Al_0.3Ga_0.2P waveguide and upper and lower 600 nm InAlP cladding layers. We observe lasing at λ∼680 nm at room temperature in optically pumped samples. [copyright] 2001 American Institute of Physics

[en] The evolution of GaAs_1-xN_x band structure at low nitrogen concentrations (up to x=0.021) is studied by ballistic electron emission microscopy (BEEM) spectra of Au/GaAs_1-xN_x heterostructures. Two peaks observed in the second derivative BEEM spectra are identified with the contribution from the Γ- and L-like bands of GaAs_1-xN_x. As the nitrogen concentration increases, the energetic separation between these peaks increases, with a relative decrease of the L-like band contribution to the BEEM current. In addition, we found a strong decrease of the Au/GaAs_1-xN_x Schottky barrier with the nitrogen incorporation, from ∼0.92 eV at x=0 down to ∼0.55 eV at x=0.021. The observed Schottky barrier reduction approximates the GaAs_1-xN_x band-gap reduction. (c) 2000 The American Physical Society