Demonstration of ultraviolet III-nitride laser diode with an asymmetric waveguide structure

Gallium nitride (GaN) ultraviolet (UV) laser diodes (LDs) show tremendous promise for optical communications, data storage, and medical applications due to their compact size and higher efficiency compared to gas lasers. Typically, GaN UV LDs utilize a symmetric waveguide structure surrounding a multiple quantum well (MQW) active region for optical confinement. By increasing the thickness of these waveguides, device performance can be enhanced by reducing absorption losses. However, thin waveguides offer decreased carrier losses and improved electrical performance. These two competing effects can be balanced through the use of an asymmetric waveguide structure, composed of a thin upper waveguide and thick lower waveguide, in order to minimize both carrier (hole) losses as well as optical losses. Here, we demonstrated an edge-emitting ridge waveguide UV GaN LD emitting at ~392 nm. Mirror facets were fabricated through reactive ion etch and potassium hydroxide wet etch. These LD structures with InGaN/GaN MQWs and AlGaN cladding layers were grown via metalorganic chemical vapor deposition on a patterned sapphire substrate and utilize an asymmetric 100 nm thick upper unintentionally doped GaN (uGaN) waveguide and 500 nm thick lower uGaN waveguide structure. We have successfully demonstrated a LD device with 1000 μm cavity length with a lasing threshold of 2.2 A, and 111.8 mW per facet peak optical output power with a differential efficiency of 3%. This demonstration paves the way for GaN LDs with improved differential efficiency at high current densities through the use of optimized asymmetric waveguide structures.