Chapter Twelve – Exploring the Next Phase in Gallium Nitride Photonics: Cubic Phase Light Emitters Heterointegrated on Silicon

Gallium nitride (GaN) materials are the backbone of emerging solid-state lighting. To date, GaN research has been primarily focused on hexagonal phase devices due to the natural crystallization. This approach limits the output power and efficiency of light-emitting diodes (LEDs), particularly in the green spectrum. However, GaN can also be engineered to be in cubic phase. Cubic GaN has a lower bandgap (~ 200 meV) than hexagonal GaN that enables green LEDs much easily. Besides, cubic GaN has more isotropic properties (smaller effective masses, higher carrier mobility, higher doping efficiency, and higher optical gain than hexagonal GaN) and cleavage planes. Due to phase instability, however, cubic phase materials and devices have remained mostly unexplored. Here we review a new method of cubic phase GaN generation: hexagonal-to-cubic phase transition, based on novel nanopatterning. We report a new crystallographic modeling of this hexagonal-to-cubic phase transition and systematically study the effects of nanopatterning on the GaN phase transition via transmission electron microscopy, temperature-dependent cathodoluminescence, and electron backscatter diffraction experiments. In summary, silicon-integrated cubic phase GaN light emitters offer a unique opportunity for exploration in next-generation photonics.