Electron-beam lithography and chemically assisted ion beam etching for the fabrication of grating surface-emitting broad-area AlGaAs lasers

We report on the fabrication and characterization of broad-area, grating-coupled, distributed Bragg reflector, surface-emitting, AlGaAs/GaAs laser diodes. Electron-beam lithography and chemically assisted ion-beam etching (CAIBE) were used to fabricate both first-order (120-nm period) and second-order (240-nm period) gratings. Gratings were patterned by exposing PMMA resist using 50-keV electrons in a JEOL 5DIIU direct write electron-beam lithography system. The resist image was transferred into the AlGaAs layer by CAIBE. CAIBE was performed using chlorine gas in conjunction with a 500-eV argon-ion beam in a modified Technics Plasma GmbH RIB 160 etcher. Surface-emitting lasers using second-order gratings were fabricated on AlGaAs/GaAs asymmetric separate confinement double heterostructure layers grown by liquid-phase epitaxy. Wet chemical etching was used to remove the upper cladding layer, exposing the waveguide in selected areas. Gratings were then etched into the waveguide to produce surface emitting window regions. The far-field light intensity pattern shows a lateral angular spread of 2.4° for a 50-μm-wide stripe. This lateral angular distribution is the lowest reported for a broad-area (not array) grating surface-emitter.