PhD Defense: "Dry Etched Features for Advanced Waveguide Design in GaN Laser Diodes"

Joseph Nedy

May 2nd (Monday), 9:00am
Engineering Science Building (ESB), Room 1001

Blue and violet laser diodes (LDs) made from the (Al,In)GaN material system were first demonstrated in 1995 [1] and have since been commercialized for applications in data storage 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 [2]. 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 [3,4] and lattice-matched quaternary alloys [5].

In this talk, 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 a blue (450 nm) laser diode. 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 [6]. The resulting process is a new fabrication method for surface etched nano-structures in GaN light emitting devices.

[1] Nakamura, S., et al., Japanese Journal of Applied Physics, Part 2: Letters, 35 (1996)
[2] Lee, C., et al., Optics Express, 23 (2015)
[3] Pourhashemi, A., et al., Applied Physics Letters 106 (2015)
[4] Mughal, A.J., et al., Electronic Letters. 52, 304 (2016)
[5] Katayama, K., et al., Electronics and Communications in Japan 98, 9 (2015)
[6] Nedy, J., et al., Semiconductor Science and Technology 30, 8 (2015).

Hosted by: Professor Jim Speck