We report further progress in the design and fabrication of high-order Bragg gratings defined by I-line projection lithography that are implemented in a high-power diode laser. Simulations of surface Bragg gratings with large duty cycles predict large reflectivities even for the 25th Bragg order. We implemented such Bragg gratings in high-power diode lasers and compared the spectral and electro-optical properties with diode lasers having seventh-order Bragg gratings. Details of the fabrication and encapsulation of the Bragg gratings will also be presented.
The electrical properties of different metal systems for ohmic contacts on the nitrogen-face of c-plane n-type GaN substrates are investigated. The metal contacts are compatible with the fabrication process and the packaging technology for group III-nitride laser diodes. The metal system Ti/Al/Mo/Ti/Ni/Au/Ti/Pt is determined as the best suitable, since it is ohmic already after annealing at a temperature of 450°C for 60 s. This annealing temperature is high enough to make the contact insensitive against later soldering on a heat-sink at 330°C. At the same time, the temperature is low enough that the Pd-based p-contact, previously annealed at 530°C, does not degrade. In addition, the Ti/W/Al and Pd/Ti/Al metal systems form low-resistance ohmic contacts, too, although they require a longer annealing time of several minutes or a higher temperature of 500°C.Index Terms-GaN laser diodes, contacts to n-GaN, N-face GaN, GaN wet-chemical etching, TMAH.
Y-branch coupled distributed-feedback lasers with 40th-and 80th-order surface Bragg gratings have been fabricated using a process based on I-line wafer stepper lithography. The devices allow dual wavelength lasing at around 975 nm. Wavelength spacing of 0.5 and 4 nm have been achieved by using grating period differences of 2.9 and 47.6 nm for the 40th-and 80th-order gratings, respectively. The manufactured devices with internal wavelength stabilization work as master oscillator power amplifiers with two separate and one common amplifier sections. We present optical output characteristics of the devices under continuous wave operation.
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