Source: http://tops.osa.org/ome/abstract.cfm?uri=ome-8-5-1221
Timestamp: 2019-04-21 04:30:59+00:00

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A specially designed InGaN/GaN superlattice (SL) interlayer was inserted between n-GaN and a multiple quantum well to enhance the performance of yellow light-emitting diodes (LEDs) grown on Si (111). The number of SL periods was determined to be the key to enhancing the external quantum efficiency and reducing forward voltage. Our results show that more SLs could suppress nonradiative recombination by eliminating micron-scale indium-rich clusters and could promote hole injection with increased V-pit size. However, too many SLs reduce the effective luminescence area and lead to many voids formed in the p-type layer. We demonstrate that 32 is the optimum number of SLs for yellow InGaN/GaN LEDs, obtaining a high light output power of 63 mW with a dominant wavelength of 568 nm, and a low forward voltage of 2.38 V at 200 mA (20 A/cm2).
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Ping-Chieh, T. A. Y. S.
Fig. 1 Schematic of the epitaxial structure of the three samples with varied number of SL periods.
Fig. 2 PL Spectra of the three samples, obtained by excitation with 410-nm laser light at room temperature.
Fig. 3 Omega-2theta scan spectra of the yellow InGaN LED structures grown on silicon substrates, obtained with HRXRD (PANalytical X’Pert).
Fig. 4 FL images of sample A (a), with 16 SL periods, sample B (b), with 24 SL periods, and sample C (c), with 32 SL periods. The images were obtained through excitation with 420–490-nm intense fluorescent light.
Fig. 5 Comparison of EQE and forward voltage among samples with different numbers of SL periods. All the samples have the same dominant wavelength of 568 nm at 200 mA.
Fig. 6 Diagrams explaining the opposite effects of (a) N-ICs and (b) M-ICs on luminescence. Within the M-ICs, many nonradiative centers (e.g., dislocations) are generated in the merged regions, as shown by the short red lines, leading to a reduced radiation recombination rate.
Fig. 7 (a), (b), and (c)SEM images of the V-pits for the three samples, obtained with a HITACHI SU8010 SEM system; (d) diagram showing the two ways to inject holes into the MQWs: via the flat area or via the side-walls of V-pits.
Fig. 8 Atomic force microscopy (AFM) images of the surface of the p-type GaN layers of LEDs with varied SL periods. The numbers of SL periods are 16 ((a) and (e)), 24 ((b) and (f)), 32 ((c) and (g)), and 40 ((d) and (h)).
Fig. 9 (a) Optical photograph of the emitting LED. (b) EL spectra and (c) light output power as a function of the injection direct current of sample C with 32 SLs.

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