Fabrication and Characterization of Surface Grating DFB Lasers Using AlGaAs/GaAs Quantum Well Material

[摘要] The aim of the research project was to fabricate and characterize surface grating DFB lasers, using AlGaAs/GaAs quantum well material, and also demonstrate its potential for integration. The operation of this surface grating DFB laser combines both lateral optical confinement and distributed feedback provided by gratings etched along the side of the laser stripe in the top cladding layer. The material structure was optimized for this type of device, consisting of two 80A GaAs quantum wells surrounded by a 0.7mum thick 40% AlGaAs top cladding layer and a 0.5mum thick 80% AlGaAs lower cladding layer. The typical lasing wavelength was about 860nm. Research concentrated on establishing a reliable fabrication process for surface 3rd-order, 2nd-order and 1st-order gratings DFB lasers using a combination of electron-beam lithography technology and reactive ion etching (RIE). The fabrication process of 3rd-order and 2nd-order grating structures was optimised and consisted of transferring an e-beam generated pattern to a 150 nm thick SiO2 layer. This patterned SiO2 layer was then used as a dry-etching mask of the AlGaAs/GaAs material. Measurement of the coupling coefficient of surface 3rd-order grating DFB waveguides was performed using a transmission technique. Maximum coupling coefficient values of 10cm-1 and 15 cm-1 were measured in 1mum deep surface grating waveguides, respectively for fundamental and second transverse modes. Dependence of the coupling coefficient on the stripe width and grating etch depth were studied, which allowed optimization of the waveguide. The light-current characteristics and spectral behaviour of surface 3rd-order, 2nd-order, and 1st-order grating DFB lasers were assessed in pulsed and CW operation. Typical values for threshold current, threshold current density, and slope efficiency were respectively, 25mA, 1400A cm-2, and 0.25mW/mA per facet in CW operation for 500 mum long devices. The stopband width was measured near threshold in surface Brd-order grating DFB lasers; using this value, the coupling coefficient was estimated to be K=9cm-1. The dependence of the FP and DFB modes on the temperature of operation was measured, in uncoated devices, to be 0.36nm/

[发布机构] University:University of Glasgow

[关键词] Electrical engineering, Condensed matter physics