UC Santa Barbara

Blue and violet laser diodes (LDs) made from the (Al,In)GaN material system were first demonstrated in 1995 and have since been commercialized for applications in data torage and display technology. As the material and device technology continues to mature, these laser diodes are being investigated for use in solid state lighting and wireless communications, most recently being utilized for high-end automobile headlights. Competitiveness in these markets will require new device designs of GaN-based LDs to improve the efficiency and optical output power.

A key structural element of a laser diode is the set of cladding layers around a waveguiding core which, together, confine the optical mode. This confinement is dependent on the refractive index contrast between the cladding and core. However, it is difficult to grow lattice-mismatched AlGaN and InGaN layers with high enough composition and thickness to provide the required index contrast. Therefore, research efforts have begun to explore new low index cladding options such as transparent conductive oxides and lattice-matched quaternary alloys.

In this work, I explore an alternative cladding design using etched nano-structures to lower the effective refractive index and create a high index-contrast top cladding layer. I present detailed simulations, design, and fabrication of blue (435.5nm, 451nm) laser diodes. I also consider the effect of sub-surface dry etch damage which can destroy the light emitting active region. While prior work on light emitting GaN nano-structures required GaN regrowths or recovery anneals, I have developed a low-damage dry etch that avoids the etch damage issue. The resulting process is a new fabrication method for surface etched nano-structures in GaN light emitting devices.