Group-III-nitride semiconductors have shown enormous potential as light sources for full-colour displays, optical storage and solid-state lighting. Remarkably, InGaN blue- and green-light-emitting diodes (LEDs) emit brilliant light although the threading dislocation density generated due to lattice mismatch is six orders of magnitude higher than that in conventional LEDs. Here we explain why In-containing (Al,In,Ga)N bulk films exhibit a defect-insensitive emission probability. From the extremely short positron diffusion lengths (<4 nm) and short radiative lifetimes of excitonic emissions, we conclude that localizing valence states associated with atomic condensates of In-N preferentially capture holes, which have a positive charge similar to positrons. The holes form localized excitons to emit the light, although some of the excitons recombine at non-radiative centres. The enterprising use of atomically inhomogeneous crystals is proposed for future innovation in light emitters even when using defective crystals.

Specular, planar semipolar gallium nitride films were grown by hydride vapor phase epitaxy. Planar films of ð10 1 1 3 3Þ and ð11 2 22Þ GaN have been grown on ð10 1 10Þ m-plane sapphire. The in-plane epitaxial relationship for ð10 1 1 3 3Þ GaN was ½30 3 3 2 2 GaN k ½1 2 210 sapphire and ½1 2 210 GaN k ½0001 sapphire . The in-plane epitaxial relationship for ð11 2 22Þ GaN was ½11 2 21 GaN k ½0001 sapphire and ½1 1 100 GaN k ½1 2 210 sapphire . The ð10 1 13 3Þ films were determined to have N-face sense polarity and a threading dislocation density of 9 Â 10 8 cm À2 . The ð11 2 22Þ films have Ga-face sense polarity and have a threading dislocation density of 2 Â 10 10 cm À2 . The basal plane stacking fault density was 2 Â 10 5 cm À1 for both orientations. The RMS roughness of the films was under 10 nm for a 5 Â 5 mm 2 area.

Nonpolar (112¯0) a-plane InGaN∕GaN multiple-quantum-well light-emitting diodes were grown by metalorganic chemical vapor deposition on reduced-defect density hydride-vapor-phase-epitaxy lateral epitaxially overgrown a-plane GaN templates. Direct current output power of 240 μW was measured at 20 mA for a 300×300μm2 device, and dc output powers as high as 1.5 mW were measured at 250 mA. DC electroluminescence (EL) measurements yielded a peak at 413.5 nm, corresponding with the room-temperature photoluminescence peak. The EL peak position was independent of drive current and a 23.5 nm linewidth was realized at 20 mA. The current–voltage characteristics of these diodes showed a forward voltage (Vf) of 3.3 V with a series resistance of 7.8 Ω.

We demonstrate the growth and fabrication of a semipolar (101¯3¯) InGaN∕GaN green (∼525nm) light emitting diode (LED). The fabricated devices demonstrated a low turn-on voltage of 3.2V and a series resistance of 14.3Ω. Electroluminescence measurements on the semipolar LED yielded a reduced blueshifting of the peak emission wavelength with increasing drive current, compared to a reference commercial c-plane LED. On-wafer measurements yielded an approximately linear increase in output power with drive current, with measured values of 19.3 and 264μW at drive currents of 20 and 250mA, respectively. The external quantum efficiency did not decrease appreciably at high currents. Polarization anisotropy was also observed in the electroluminescence from the semipolar green LED, with the strongest emission intensity parallel to the [12¯10] direction. A polarization ratio of 0.32 was obtained at a drive current of 20mA.