15 May 2020
University of California Santa Barbara in the USA has been developing techniques to grow and separate gallium nitride (GaN) semi-polar and non-polar epitaxial layer overgrowth (ELO) bars on native substrates [Srinivas Gandrothula et al, Appl. Phys. Express, vol13, p041003, 2020]. Such material could lead to lower-cost manufacturing of efficient light-emitting diodes (LEDs) and laser diodes, particularly for longer green and beyond wavelengths greater than 500nm.
The hope is that the process would lead to recycling of the prohibitively expensive GaN native growth substrates. The non-/semi-polar crystal orientation can eliminate or even reverse spontaneous or strain-dependent electric fields in devices, which inhibit the recombination of electrons and holes into photons in the usual polar c-plane GaN and associated heterostructures. The researchers see potential for automotive headlights, specialty lighting, displays, augmented reality/virtual reality (AR/VR) and light fidelity communication.
Although the researchers have not produced functional devices on the bars, they comment: “We believe that the demonstrated top width of ELO bars on several semi-polar planes can comfortably accommodate micro-LEDs or edge-emitting lasers, including electrical pads.” Also, last year, the UCSB group used a related technique to produce laser bars with a low threshold current density of 2.15kA/cm2 [Takeshi Kamikawa et al, Optics Express, vol27, p24717, 2019].
Full text re. image attachment.
Figure 1: (a) ELO mask design on native semi-polar GaN substrate, (b) schematic of grown ELO bars from open window, (c) magnified top-view scanning electron microscope mages of ELO bars, (d) left and right vertical axis, respectively, indicate top width and vertical to horizontal growth of semi-polar ELO bars against angle measured from m-plane.