The performance of conventional c-plane GaN-based optoelectronic devices suffers from the effects of strong polarization-induced electric fields along the conduction direction, which result in a reduced overlap between electron and hole wavefunctions. These devices consequently demonstrate low radiative recombination rates, and a blue-shift in peak emission wavelength with increasing bias. There have been several recent demonstrations of light emitting diodes (LEDs) fabricated on non-polar a- and m- plane GaN that show greatly reduced to zero blue-shift of peak emission wavelength, and other recent work on non-polar GaN has yielded hole concentrations that are almost an order of magnitude higher than for c-plane GaN.
The effects of the strong polarization-induced electric fields may, conceivably, also be mitigated or potentially eliminated by growing films on so-called ‘semipolar’ planes. A semipolar plane is any plane that may not be classified as a c-, a- or m- plane, and has at least two non-zero h, i, or k Miller indices and a nonzero l Miller index (, and planes, for example). It is expected that devices grown on these semipolar planes should also demonstrate a reduced blue-shift in peak emission wavelength and higher hole concentrations. Further, recent work also suggests that the indium incorporation efficiency for growth on semipolar planes is comparable to that for growth on the c-plane.
We demonstrate the first green InGaN/GaN LED grown on a planar semipolar GaN template. The LED structure is grown by metalorganic chemical vapor deposition (MOCVD), and the 20 μm-thick, specular and optically transparent template is grown by hydride vapor phase epitaxy (HVPE). The fabricated devices have a peak emission wavelength of ∼525 nm and demonstrate rectifying behavior, with a low turn-on voltage of 3.2 V. We observe a small ∼7 nm blue-shift in the peak emission wavelength during electroluminescence measurements, over the range 20 to 250 mA. We also see an almost linear increase in the output power from 5 mA to 200 mA, with no appreciable decrease in the external quantum efficiency over the same range. We also observe evidence of polarization anisotropy in the emission from the semipolar green LEDs.