Optical emission characteristics of semipolar (1122) GaN light-emitting diodes grown on m-sapphire and stripe-etched r-sapphire.

We demonstrate the growth and optical characterization of semipolar (1 1 &2macr; 2) GaN light-emitting diodes (LEDs) on sapphire utilizing two distinct heteroepitaxial growth methodologies. The properties of semipolar (1 1 &2macr; 2) LEDs are analyzed by the simultaneous growth of LED structures on templates prepared by both two-step growth on m-sapphire and selective growth on etched r-plane sapphire. Typically, growth on m-sapphire yields a high density of microstructural defects and surface morphological features which complicate the understanding of emission properties in devices. In this study, we find improved spectral properties of devices grown on etched r-sapphire due to improved surface roughness and microstructural quality (x-ray diffraction rocking curves of 280-550 arcsec for on-axis (1 1 &2macr; 2) and off-axis (101n), n = 0-5 diffractions), and reveal that the commonly observed broad emission and sub-bandgap peak in semipolar LEDs on sapphire are caused by a tunneling-assisted radiative recombination mechanism. [ABSTRACT FROM AUTHOR]