Characterization of Gallium Nitride Grown on Patterned Sapphire Substrate with Shallow U-Shaped Stripe Grooves

Lee, Ko-Tao; Lee, Yeeu-Chang; Chang, J. S.

doi:10.1149/1.2952807

Cited by 4 publications

(4 citation statements)

References 23 publications

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“…[11][12][13][14][15][16] On the other hand, the patterns on the PSS can reduce the threading dislocations in the GaN epitaxial layers owing to the possible lateral growth of the GaN epi-layer. 2,5,6,8,17 Some recent studies indicated that the use of nano-scale patterned sapphire substrate leads to increase in IQE, which is resulted from the significant reduction in the threading dislocation density (two-orders of magnitude reduction) and reduction in the fraction of the screw dislocation density. [18][19][20][21] Besides, some researchers also indicate that IQE can be improved by QW designing (for examples, non-polar QW and large overlap QW).…”

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confidence: 99%

Pattern-Coverage Effect on Light Extraction Efficiency of GaN LED on Patterned-Sapphire Substrate

Lin

Chen

Chang

et al. 2012

Electrochem. Solid-State Lett.

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GaN-based LEDs were fabricated on patterned-sapphire substrates with various pyramidal-pattern coverage percentages (31-81%). Three distinguish stages are observed in the behavior of the light out-put power against coverage percentage. By etching-pit density measurement, dislocation density is found to be independent with coverage percentage. The light extraction efficiency (LEE) should be the main mechanism for the enhancement in the light out-put power. LEE would be enhanced, when the pattern coverage is less than 39% or over 67%. The light extraction efficiency remains similar, when the pattern coverage in between 39% ∼ 67%.The sapphire substrate patterning technique has been widely used to improve the external quantum efficiency (EQE) of GaN-based LEDs. 1-10 The improvement obtained using the patterned-sapphire substrate (PSS) technique includes the enhancements of both the internal quantum efficiency (IQE) and light extraction efficiency (LEE). The LEE is enhanced because of the patterns on the PSS act to destroy the TIR (Total Internal Reflection) effect at the GaN/sapphire interface. 1, 3, 4 Several published literatures have pointed out that the light extraction efficiency could be increased by using periodic or non-periodic micron-sized patterning on sapphire substrate. 11-16 On the other hand, the patterns on the PSS can reduce the threading dislocations in the GaN epitaxial layers owing to the possible lateral growth of the GaN epi-layer. 2,5,6,8,17 Some recent studies indicated that the use of nano-scale patterned sapphire substrate leads to increase in IQE, which is resulted from the significant reduction in the threading dislocation density (two-orders of magnitude reduction) and reduction in the fraction of the screw dislocation density. 18-21 Besides, some researchers also indicate that IQE can be improved by QW designing (for examples, non-polar QW and large overlap QW). [22][23][24][25][26][27][28][29] Generally, it seems that the greater the pattern coverage created on the PSS, the higher the LEE would be. 30 However, there so far been no any experimental study or systematically investigation of the effect of the pattern coverage of the PSS on the and LEE. Another key issue that is not yet well understood is how does the pattern coverage (or c-plane coverage) influence the IQE of a GaN-based LED on the PSS. In this study, a mask-free wet-etching process is used to produce a so-called naturally patterned-sapphire substrate (n-pss). 31 By varying the etching time and temperature, different amount of pyramidal pattern coverage can be created on the n-pss wafers. The effect of the pyramidal pattern coverage on the IQE and LEE of the GaN epi-layers can be studied.The mask-free wet-etching process used to produce the pyramidal n-pss wafers is described in detail below. Before the wet-etching process, a PECVD (Plasma Enhanced Chemical Vapor Deposition) SiO 2 layer was deposited on the back-side of the c-plane sapphire wafers to prevent the back-side of sapphire wafers from being etched. The flat back-...

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confidence: 99%

Pattern-Coverage Effect on Light Extraction Efficiency of GaN LED on Patterned-Sapphire Substrate

Lin

Chen

Chang

et al. 2012

Electrochem. Solid-State Lett.

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“…Meanwhile, high quality c-plane GaN epitaxial layers with low dislocation densities can be achieved on maskless c-plane patterned sapphire substrates ͑PSSs͒ with periodic grooves or holes. [11][12][13] In comparison with the conventional epitaxial lateral overgrowth technique, the photolithography and epilayer growth process are simplified, and the contamination from the dielectric mask is prevented. In addition, the geometrical effect of patterned substrates can also effectively enhance light extraction, improving the optoelectronic device performance and efficiency.…”

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confidence: 99%

Hydride Vapor Phase Epitaxy Growth of Semipolar (1013)GaN on Patterned m-Plane Sapphire

Wei

Duan

Wei

et al. 2010

J. Electrochem. Soc.

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We have investigated the hydride vapor-phase epitaxy growth of ͑101 ¯3 ¯͒-oriented GaN thick films on patterned sapphire substrates ͑PSSs͒ ͑101 ¯0͒. From characterization by atomic force microscopy, scanning electron microscopy, double-crystal X-ray diffraction, and photoluminescence ͑PL͒, it is determined that the crystalline and optical qualities of ͑101 ¯3 ¯͒ GaN epilayers grown on the cylindrical PSS are better than those on the flat sapphire. However, two main crystalline orientations ͑101 ¯3 ¯͒ and ͑112 ¯2͒ dominate the GaN epilayers grown on the pyramidal PSS, demonstrating poor quality. After etching in the mixed acids, these ͑101 ¯3 ¯͒ GaN films are dotted with oblique pyramids, concurrently lining along the ͗303 ¯2 ¯͘ direction, indicative of a typical N-polarity characteristic. Defect-related optical transitions of the ͑101 ¯3 ¯͒ GaN epilayers are identified and detailedly discussed in virtue of the temperature-dependent PL. In particular, an anomalous blueshift-redshift transition appears with an increase in temperature for the broad blue luminescence due to the thermal activation of the shallow level.

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“…where C 2 is the concentration of nitrogen dimers, g 1 and g 2 are the numbers of available sites per unit cell for the monomer and dimer, respectively, ⍀ 0 is the volume of a unit cell, ⌬G 2 is the binding energy of the dimer, and D 1 and D 2 are the monomer and dimer diffusivities, respectively. 36 If the dimer is immobile ͑i.e., neglecting D 2 ͒, then a generalized expression for the nitrogen monomer diffusivity can be substituted into Eq. 2 to give…”

Section: Discussionmentioning

confidence: 99%

Measurements of Dislocation Locking by Near-Surface Ion-Implanted Nitrogen in Czochralski Silicon

Alpass¹,

Jain²,

Murphy³

et al. 2009

J. Electrochem. Soc.

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A modified dislocation unlocking technique is used to measure dislocation locking due to nitrogen implanted into Czochralski silicon. The results show that near-surface dislocations can be locked by implanted nitrogen. The magnitude of the locking measured suggests that nitrogen transport proceeds by a dissociative mechanism, where transport occurs by the splitting of immobile dimers into fast monomers, rather than movement of nitrogen dimers. In other experiments, nitrogen-doped float-zone silicon is investigated using the standard dislocation unlocking technique. The results give an activation energy for effective nitrogen diffusion in silicon of 3.24±0.25eV at 500–750°C . Using the assumption that the dislocation locking strength per nitrogen atom is the same as that of oxygen, a value of 200,000cm2normals−1 can be inferred for the effective diffusivity prefactor. If analyzed using the dissociative model, an activation energy of 1.1–1.4 eV is found for nitrogen monomer diffusion, with a diffusivity prefactor of 30cm2normals−1 .

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Characterization of Gallium Nitride Grown on Patterned Sapphire Substrate with Shallow U-Shaped Stripe Grooves

Cited by 4 publications

References 23 publications

Pattern-Coverage Effect on Light Extraction Efficiency of GaN LED on Patterned-Sapphire Substrate

Pattern-Coverage Effect on Light Extraction Efficiency of GaN LED on Patterned-Sapphire Substrate

Hydride Vapor Phase Epitaxy Growth of Semipolar (1013)GaN on Patterned m-Plane Sapphire

Measurements of Dislocation Locking by Near-Surface Ion-Implanted Nitrogen in Czochralski Silicon

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