Abstract :
Gallium nitride (GaN) and related alloys are important semiconductor materials for fabricating novel photonic devices such as ultraviolet (UV)
light-emitting diodes (LEDs) and vertical cavity surface-emitting lasers (VCSELs). Recent technical advances have made free-standing GaN
substrates available and affordable. However, these materials are strongly resistant to wet chemical etching and also, low etch rates restrict the use
of dry etching. Thus, to develop alternative high-resolution processing for these materials is increasingly important. In this paper, we report the
fabrication of microstructures in free-standing GaN using pulsed UV lasers. An effective method was first developed to remove the re-deposited
materials due to the laser machining. In order to achieve controllable machining and high resolution in GaN, machining parameters were carefully
optimised. Under the optimised conditions, precision features such as holes (through holes, blind or tapered holes) on a tens of micrometer length
scale have been machined. To fabricate micro-trenches in GaN with vertical sidewalls and a flat bottom, different process strategies of laser
machining were tested and optimised. Using this technique, we have successfully fabricated high-quality micro-trenches in free-standing GaN with
various widths and depths. The approach combining UV laser micromachining and other processes is also discussed. Our results demonstrate that
the pulsed UV laser is a powerful tool for fabricating precision microstructures and devices in gallium nitride
