A semipolar ( $$\left( {10\overline 1 \overline 3 } \right)$$ ) InGaN/GaN green light emitting diode
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A semipolar 1 0 1 3 InGaN/GaN green light emitting diode Rajat Sharma1, P. Morgan Pattison1, Troy J. Baker1, 3, Benjamin A. Haskell1, 3, Robert M. Farrell2, Hisashi Masui1, Feng Wu1, 3, Steven P. DenBaars1, 2, 3, James S. Speck1, 3 and Shuji Nakamura1, 2, 3 1
Materials and 2Electrical and Computer Engineering Departments, University of California, Santa Barbara, CA 93106, U.S.A. 3 NICP/ERATO JST, UCSB Group, University of California, Santa Barbara, CA 93106, U.S.A.
ABSTRACT We demonstrate the first green InGaN/GaN light emitting diode (LED) grown on a planar semipolar 1 0 1 3 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 operating voltage of 3.25 V at 20 mA. 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 250 mA, with no appreciable decrease in the external quantum efficiency over the same range. Additionally, we observe evidence of polarization anisotropy in the emission from the semipolar green LEDs.
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INTRODUCTION 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 [13]. 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 mplane GaN that show greatly reduced to zero blue-shift of peak emission wavelength [47], 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 [8]. 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 ( 1 0 11 , 1 0 1 2 and 1 0 1 3 planes, for example). It is expected that devices grown on these semipolar planes should also demonstrate a reduced blue-shift in peak emission wavelength [9] and higher hole concentrations [10]. Further, preliminary work also suggests that the indium
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incorporation efficiency for growth on semipolar planes is comparable to that for growth on the c-plane.
EXPERIMENTAL DETAILS
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A 20 µm-thick, specular and optically transparent semipolar 1 0 1 3 GaN template was grown using hydride vapor phase epitaxy (HVPE) on an m-sapph
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