GaN-Based Light-Emitting Diodes on Selectively Grown Semipolar Crystal Facets

In this article, we briefly review a particular approach to fabricate light-emitting diode (LED) structures on the semipolar side facets of triangular GaN stripes grown by selective area epitaxy. This approach enables a significant reduction of the internal piezoelectric fields in the LED's active area, while still maintaining the well-established c-direction as the main epitaxial growth direction for GaN-based devices on large area substrates. For the latter, these internal fields are responsible for the lower efficiency of GaN-based LEDs in the longer (green) wavelength range. The reduced internal fields of such semipolar LEDs can be directly determined by photoluminescence (PL) investigations on pre-biased LED structures and further confirmed by time-resolved PL studies. The epitaxial growth behavior is strongly facet-dependent, leading to different surface flatnesses on different semipolar facets formed by this procedure and different indium incorporation efficiencies. An increased indium uptake on semipolar {1 (1) over bar 01} facets as compared to conventional c-plane layers can help to shift the LED emission to longer wavelengths near 500 nm, despite the significantly reduced field-dependent Stark shift, which helps to reach the green wavelength range in polar LEDs.