Search

Improving current injection into r- and m-planes of nanowires (NWs) is essential to realizing efficient GaInN/GaN multiple quantum shell (MQS) NW-based light-emitting diodes (LEDs). Here, we present the effects of different p-GaN shell growth conditions on the emission characteristics of MQS NW-LEDs. Firstly, a comparison between cathodoluminescence (CL) and electroluminescence (EL) spectra indicates that the emission in NW-LEDs originates from the top region of the NWs. By growing thick p-GaN shells, the variable emission peak at around 600 nm and degradation of the light output of the NW-LEDs are elaborated, which is attributable to the localization of current in the c-plane region with various In-rich clusters and deep-level defects. Utilizing a high growth rate of p-GaN shell, an increased r-plane and a reduced c-plane region promote the deposition of indium tin oxide layer over the entire NW. Therefore, the current is effectively injected into both the r- and m-planes of the NW structures. Consequently, the light output and EL peak intensity of the NW-LEDs are enhanced by factors of 4.3 and 13.8, respectively, under an injection current of 100 mA. Furthermore, scanning transmission electron microscope images demonstrate the suppression of dislocations, triangular defects, and stacking faults at the apex of the p-GaN shell with a high growth rate. Therefore, localization of current injection in nonradiative recombination centers near the c-plane was also inhibited. Our results emphasize the possibility of realizing high efficacy in NW-LEDs via optimal p-GaN shell growth conditions, which is quite promising for application in the long-wavelength region.

Blue, green, and red micro‐light‐emitting diodes (LEDs) are expected to serve as light sources for next‐generation full‐color displays. This study fabricates an InGaN LED with an active layer comprising stacked red, green, and blue active layers separated by interlayers using the metal‐organic vapor‐phase epitaxy method for application to a monolithic full‐color LED. Experimental results and band simulations reveal that the emission wavelength during the current injection is controllable via adjustments to the Si doping amount of the interlayer. For a Si doping amount of the interlayer of approximately 2 × 1018 cm−3, only the red active layer closest to the p‐side emits light with a wavelength of ≈610 nm. With a decrease in the Si doping amount in the interlayer, the emission intensity from the n‐side active layer, that is, the green and blue active layers, increases. Moreover, the Si‐doped interlayer acts as a barrier against holes diffusing from the p‐side to the n‐side, thus controlling the amount of carrier injected into each active layer. Additionally, the green and blue active layers under the red active layer improve the emission characteristics of the red active layer. These results indicate the importance of this technology for realizing monolithic, full‐color InGaN‐based LEDs. [ABSTRACT FROM AUTHOR]

Herein, the growth mechanism and defect structure of GaN‐based nanowire multiple‐quantum‐shells (NW‐MQSs) with cap layers combining tunnel junctions and n‐GaN are investigated in detail. In the NW‐MQS structure, defect structures are formed in three regions: (i) From the c‐plane active layer at the tip of NW because of the low crystal quality of the active layer. (ii) Basal‐plane stacking faults (BSFs) with partial dislocations (PDs) are generated from the m‐planes of the NW‐MQSs; these defects are triggered by the silicon nitride (SiNx) formed on the NW surface. While some defects terminate because of the half loop formed by the PDs along the lateral growth of cap layers, others terminate at the coalesced region of the cap layers grown from adjacent MQSs. (iii) Line defects due to low‐angle grain boundaries and planar defects due to the BSFs in region (ii) are formed in the region wherein cap layers coalesce. The defects reaching the surface of the cap layers predominantly depend on the number of defects generated from the c‐plane active layers in region (i). The growth mode and propagation mechanism of such defects are associated, and a method for realizing optical devices based on the high‐quality NW‐MQS structures is discussed. [ABSTRACT FROM AUTHOR]

To achieve both the reduction of threading dislocation density (TDD) and the enhancement of light extraction efficiency (LEE) of light-emitting diodes (LEDs), a two-directional stripe-patterned sapphire substrate (TPSS) was fabricated. First, a stripe pattern parallel to the a-axis of Al2O3 was formed on an as-received c -sapphire wafer and then a second stripe pattern rotated around 3° from the m-axis of Al2O3 was formed on the first stripe PSS. The light output power of TPSS LEDs was around 1.25 times higher than that of LEDs on a flat sapphire substrate. This enhancement is caused by the increase of both the internal quantum efficiency (IQE) and the LEE. On the other hand, although the LED on TPSS with the second stripe just parallel to the m-axis of Al2O3 showed a similar enhancement ratio of the light output power, the current leakage of this LED increased with the concentration of threading dislocations on the surface of LEDs. Stripes rotated 3° from the m-axis of Al2O3 changed the growth mode and realized GaN films with a smooth surface without pit formation. Therefore, the misalignment of the stripe from the m-axis of Al2O3 will become a new design parameter for realizing high-efficiency reliable LEDs. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Low-temperature-deposited (LT-) AlN layers and the initial growth of GaN on a- and c-sapphire have been investigated and compared. The as-deposited LT-AlN layers on both a- and c-sapphire are composed of high-density islands. By annealing, the islands become large. The density of islands on a- and c-sapphire are 5.6 × 1010 and 7.9 × 1010 cm-2, respectively, indicating that the evolution of the solid phase epitaxy of AlN islands induced by annealing is different on a- and c-sapphire. The moiré spacings obtained by plan-view electron microscopy reveal that the strain of the AlN islands on a-sapphire is larger than that of islands on c-sapphire. These results imply that development of the solid phase epitaxy is influenced by the strain. The coalescence of GaN islands grown on a-sapphire, which has larger AlN islands, is advanced compared with that of islands on c-sapphire. The relationship between the annealed AlN island density and the threading dislocation (TD) density in the GaN films is investigated on a- and c-sapphire. The TD density of the GaN films is small when the density of annealed AlN islands is low. These results indicate that decreasing the island density of the annealed AlN layers is essential for improving the crystalline quality of GaN films. It is therefore important to control the solid phase epitaxy of LT-AlN layers by annealing. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The fabrication of a blue m-plane GaInN light emitting diode (LED) grown on an m-plane GaN layer grown on a 3-in. patterned sapphire substrate is reported. The output power of the LED was approximately 3 mW at the wavelength of 461 nm, a driving current of 20 mA, and a forward voltage of 3.5 V. This is the first report of nonpolar or semipolar blue LEDs grown on hetero-substrates with milliwatt scale output power. [ABSTRACT FROM AUTHOR]

Nonpolar m-plane GaN films have been grown by metalorganic vapor-phase epitaxy on patterned a-plane sapphire substrates (diameter: 3 in.) without dielectric masks made of materials such as SiO2. The m-plane GaN layer had a smooth and transparent surface over the entire area of the substrate. Furthermore, the epitaxial relationships between the m-plane GaN film and the patterned a-plane sapphire substrate were as follows: [0001]GaN∥[0001]Sapphire and [1120]GaN∥[1010]Sapphire. The full width at half maximum values of the X-ray rocking curves for (1010) GaN along [1120]GaN and [0001]GaN were found to be 396 and 565 arcsec, respectively. [ABSTRACT FROM AUTHOR]