Epitaxy and microstructure of a- and c-plane GaInN on Ni-self-assembled nanopatterned templates

Abstract

Light-emitting diodes (LEDs) hold great promise for lighting because of their capability to efficiently convert electricity to light. Near 90% efficiency has been achieved for GaN-based LEDs emitting 440 nm blue light. For many applications, LEDs of longer wavelengths are also desired. Attempts to extend the successes of the blue LED to longer wavelengths have so far proved challenging. Fundamental material challenges of the GaN/GaInN material system, primary among them high extended defect densities and polarization fields, directly cause or exacerbate device performance challenges of efficiency droop, wavelength shift and the green gap. These challenges are interrelated and therefore must be considered simultaneously to achieve progress.

Low-defect GaInN films are a promising foundation for efficient, long-wavelength device structures which will enable transformational applications in lighting.

This nanopatterning technique, originally applied to GaN regrowth, is now used to grow thick GaInN films of up to 0.13 InN fraction at growth rates up to 1.2 μm/h. The drastic reduction of extended defects in GaN films achieved through nanopatterning is achieved here for GaInN films as well where 75% reduction of extended defects is found compared to the GaN template. Further, the amount of defect reduction provided by the nanopatterning is found here to be insensitive to the composition of the regrown GaInN suggesting this is a promising means to achieve low-defect GaInN of even higher InN content. Both the non-polar a- and traditional, polar c-plane GaInN orientations are explored here. The a-plane orientation, relatively unexplored up until now for thick GaInN films, shows some fundamental advantages over that of traditional c-plane for the growth of smooth, high InN content GaInN layers.

In this work, a strategy to address these challenges is outlined and progress on its implementation is presented. One aspect of this strategy involves the use of nanopat-terned templates for material regrowth by metalorganic vapor phase epitaxy. This nanopatterning technique is found both here and by others to be highly effective at uniformly reducing extended defects in regrown materials by up to 90%. The mecha-nisms leading to this drastic extended defect reduction are explored here, including with an X-ray diffraction characterization method which was developed in this work.