June 15, 2017: Researchers at the University of California, Santa Barbara (UCSB) have developed an alternative design of blue-emitting laser that has a current aperture formed by photoelectrochemical etching.
Ludovico Megalini, spokesman for the UCSB team, said that this work shows that selective lateral etching, in a controllable way, is possible in a complex nitride-based structure, such as a laser diode.
The researchers etched an InGaN-based active region from GaN-based bottom and top epilayers, but this could be applied also to etch GaN layers from AlGaN-based bottom and top epilayers.
Another breakthrough of this work is that it shows how to make nitride-based optoelectronic devices, and eventually electronic devices, that deliver superior performance to those made with traditional dry etching techniques. Reactive-ion etching and inductively-coupled-plasma etching are known to cause sub-surface damage to the epitaxial structure.
Another advantage of photoelectrochemical etching, which is an established technique for etching silicon and zinc blende III-Vs, is that it is not just a technique for the lab ? it can be used for high-volume manufacturing.
The researchers at UCSB fabricated their novel laser by applying a photoelectrochemical etch to an epistructure with an InGaN/GaN active region formed on the (20-2-1) plane of GaN. To create the current aperture, they added an opaque metal mask. This blocked light needed to generate carriers during the photoelectrochemical etching step involving potassium hydroxide.
After etching, the formed 1800 µm stripe-length lasers with an 8 µm wide ridge width and an active region width of 2.5 µm. Comparisons were then made between this chip and a shallow-etched laser with an identical strip-length. This control had a p-GaN ridge width and active region width of 2.5 µm and an etch depth of 420 nm (the remnant p-side thickness is 220 nm).
Source: Compound Semiconductor