Gallium nitride-based, double-heterostructure diode laser emits blue light
Researchers at Boston University (Boston, MA) have entered the blue laser fray with the first gallium nitride-based, double-heterostructure diode laser to emit blue light. The optically pumped indium gallium nitride/gallium nitride (InGaN/GaN) devices were grown on a sapphire substrate, and the laser cavities were fabricated by cleaving. To grow the devices, the grou¥initially deposited a 10-µm-thick buffer layer of GaN on c-plane sapphire, using hydride vapor-phase epitaxy. After that a 0.5-µm GaN bottom cladding layer, a 1000-Å InGaN:Si active region and a 2200-Å GaN to¥cladding layer were deposited by metal-organic vapor-phase epitaxy.
The devices were pumped with a nitrogen laser emitting at 337 nm with a pulsewidth of 800 ps and a maximum power density of 98 MW/cm2. Above the incident threshold intensity of 1.3 MW/cm2, the researchers observed a shar¥emission peak at about 395 nm. The peak achieved a minimum full width at half maximum of 13.5 meV at an incident intensity of 3.1 MW/cm2. The researchers point to the simultaneous occurrence of a shar¥reduction in linewidth along with a shar¥increase in quantum efficiency and high TE polarization on passing the incident threshold power density as evidence of lasing. The grou¥also expects that the double heterostructure will avoid potential problems associated with multiple-quantum-well devices, such as high resistance and nonuniform excitation.