Transmission Electron Microscopy Investigation of Dislocations in GaN Layer    Grown by Facet-Controlled Epitaxial Lateral Overgrowth

Honda, Y.; Iyechika, Yasushi; Maeda, Takuya; Miyake, Hideto; Hiramatsu, Kazumasa

doi:10.1143/jjap.40.l309

Cited by 34 publications

(27 citation statements)

References 6 publications

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“…3(b), around the void, the other annihilation mechanism of the dislocations is bending due to the ELO effect. The dislocations are bent in a way unlike that of the line bending in the case of the ELO GaN [13]. This dislocation behavior is like that observed in the case of the growth of planar c-AlN or ELO cAlN [12,14].…”

supporting

confidence: 60%

Microstructure of a‐plane AlN grown on r‐plane sapphire and on patterned AlN templates by metalorganic vapor phase epitaxy

Okada

Imura

Nagai

et al. 2007

Phys. Status Solidi (c)

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The growth of a-plane AlN (a-AlN) on r-plane sapphire substrate and the epitaxial lateral overgrowth (E-LO) of a-AlN on patterned a-AlN has been performed by high-temperature metalorganic vapor phase epitaxy. The ELO a-AlN layers coalesced well on the a-AlN template with trenches formed along <10 1 0>. A detailed study of the microstructure by transmission electron microscopy revealed that the stacking faults due to facet slip are completely annihilated above the trenches of the patterned AlN. Furthermore, a dislocation density as low as 9.1×10 7 cm -2 was achieved by ELO.1 Introduction Recently, a 210 nm ultra-violet (UV) light-emitting diode has been fabricated using AlN as an active layer [1]. In response, AlN is much more attractive as a material for UV emitters or their underlying layers. To fabricate UV devices, it is desirable to use AlN as the underlying layer as it can be an effective window for UV light due to its wide band gap. In addition, cracking due to tensile stress can be suppressed if AlGaN is grown on AlN. However, the external quantum efficiency of UV emitters is low and decreases with increasing Al-content in AlGaN owing to many problems, such as decreasing electron or hole concentration on n-or p-layers and high-density dislocations in the layer [2,3]. In addition, another problem is the internal electric field induced by piezoelectricity in the heterostructures of the quantum wells on the polar c-planes [4]. To avoid this adverse effect, nonpolar planes such as the a-plane and m-plane have attracted much attention for the improvement of the efficiency. From this point of view, a nonpolar AlN plane substrate is one of the ideal substrates for UV devices. However, nonpolar epitaxial layers, such as a-GaN layers, have high-density dislocations, and the crystalline quality of a-AlN on r-plane sapphire reported to date is inferior to that of c-plane AlN on c-plane sapphire because of many defects, such as threading dislocations and stacking faults [5,6]. To improve the crystalline quality of a-AlN, we succeeded in achieving the epitaxial lateral overgrowth (ELO) of an a-AlN layer [7] by high-temperature metal-organic vapor phase epitaxy (HT-MOVPE) [8].In this study, the microstructures of a-AlN on r-sapphire and an ELO a-AlN layer grown on patterned AlN were determined via transmission electron microscopy (TEM).

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supporting

confidence: 60%

Microstructure of a‐plane AlN grown on r‐plane sapphire and on patterned AlN templates by metalorganic vapor phase epitaxy

Okada

Imura

Nagai

et al. 2007

Phys. Status Solidi (c)

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“…The lateral and vertical growth rates of the GaN films were very sensitive to the growth temperature and the mole fraction of the reactant gas. Since the lateral growth of GaN among the silica balls was increased by increasing the group V/III ratio, TMG flow rates of 23 and 37 lmol min -1 were used for high lateral and vertical growth rates, respectively [20,21].…”

Section: Methodsmentioning

confidence: 99%

Heteroepitaxial Growth of High‐Quality GaN Thin Films on Si Substrates Coated with Self‐Assembled Sub‐micrometer‐sized Silica Balls

Hong

et al. 2006

Advanced Materials

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The heteroepitaxial growth of compound semiconductors on Si substrates has great potential for Si-based optoelectronic device applications. The heteroepitaxy on Si offers low-cost and large-scale processing as well as attractive thermal and electrical conductivities for high-performance optoelectronic device operation. Furthermore, group III-V compound semiconductors on Si substrates would yield optical communication in integrated circuits. Although substantial efforts have been made to grow heteroepitaxial compound semiconductor films on Si for optoelectronic device applications, it remains very difficult to prepare high-quality compound semiconductors on Si substrates when there are large differences in lattice parameters and thermal expansion coefficients between the thin film and the Si substrate. In general, a high density of dislocations and cracks is generated for typical lattice-mismatched compound semiconductor systems, including GaN films on Al 2 O 3 and Si substrates. [1,2] Although epitaxial lateral overgrowth (ELO) of GaN layers on sapphire and Si substrates with a patterned thin-film mask exhibited a reduced dislocation density, [3][4][5] a micropatterned mask layer of SiO 2or SiN x needs to be used for the lateral growth, which means that complicated photolithography, thin-film deposition, and growth interruption are inevitable. [6][7][8][9] Meanwhile, a simple maskless overgrowth technique without the need for either lithography or growth interruption can simplify the growth process, which would be very helpful for achieving high-yield and low-cost device fabrication. In this communication, we report on the maskless heteroepitaxial growth of GaN on a Si substrate with a self-assembled sub-micrometer-sized silicaball layer.Monodisperse sub-micrometer-sized silica balls were employed as an intermediate layer for the heteroepitaxial growth of GaN layers on Si(111) substrates. The silica balls were prepared by a previously reported method, [10] and exhibited a typical diameter of 500 nm with a uniform size distribution. Such a uniform particle size allows monodisperse silica-ball arrays to be prepared on substrates by simple methods, including dip-coating, spin-coating, and spray techniques. The silica-ball-coated Si (SBS) substrates were used for the growth of GaN thin films by low pressure metallo-organic vapor phase epitaxy (MOVPE). [11] Prior to the GaN layer growth, 80 nm thick AlN buffer layers were deposited on the SBS substrates in order to prevent meltback etching. [12,13] The typical thickness of GaN epilayers after growing for 80 min was 1.4 lm. Field-emission-gun scanning electron microscopy (FEG-SEM) and optical microscopy were employed to investigate the surface morphology of the GaN epilayers on SBS substrates at different growth stages. Figure 1a shows an SEM image of the monodisperse silica-ball array dispersed on a Si(111) substrate. The silica balls were self-assembled to a hexagonally well-ordered packing structure. Meanwhile, Figure 1b and c shows SEM images of a GaN film on an SB...

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“…The standard two step growth process uses a GaN NL and one set of high temperature growth conditions, which results in rapid coalesce of the GaN nuclei and dislocation densities in the range from 1 to 5x10 9 cm -2 . More recently, several groups, including us, have been using a three step growth process which uses a GaN NL and two sets of high temperature growth conditions [7]. Using this three step method, we have recently achieved dislocation densities as low as 4x10 8 cm -2 .…”

Section: Gan Nucleation and Initial Stages Of Growthmentioning

confidence: 99%

“…Using the AFM technique on four 3 μm x 3 μm images we measured screw and mixed dislocation density of 3.1x10 7 cm -2 and a edge dislocation density of 5.0x10 7 cm -2 for sample DNZ01883 which is shown in Fig. 26 …”

Section: Task 3 Summarymentioning

confidence: 99%

Nanostructural engineering of nitride nucleation layers for GaN substrate dislocation reduction.

Koleske¹,

Lee²,

Lemp³

et al. 2009

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With no lattice matched substrate available, sapphire continues as the substrate of choice for GaN growth, because of its reasonable cost and the extensive prior experience using it as a substrate for GaN. Surprisingly, the high dislocation density does not appear to limit UV and blue LED light intensity. However, dislocations may limit green LED light intensity and LED lifetime, especially as LEDs are pushed to higher current density for high end solid state lighting sources. To improve the performance for these higher current density LEDs, simple growthenabled reductions in dislocation density would be highly prized.GaN nucleation layers (NLs) are not commonly thought of as an application of nano-structural engineering; yet, these layers evolve during the growth process to produce self-assembled, nanometer-scale structures. Continued growth on these nuclei ultimately leads to a fully coalesced film, and we show in this research program that their initial density is correlated to the GaN dislocation density.In this 18 month program, we developed MOCVD growth methods to reduce GaN dislocation densities on sapphire from 5x10 8 cm -2 using our standard delay recovery growth technique to 1x10 8 cm -2 using an ultra-low nucleation density technique. For this research, we firmly established a correlation between the GaN nucleation thickness, the resulting nucleation density after annealing, and dislocation density of full GaN films grown on these nucleation layers. We developed methods to reduce the nuclei density while still maintaining the ability to fully coalesce the GaN films. Ways were sought to improve the GaN nuclei orientation by improving the sapphire surface smoothness by annealing prior to the NL growth. Methods to eliminate the formation of additional nuclei once the majority of GaN nuclei were developed using a silicon nitride treatment prior to the deposition of the nucleation layer. Nucleation layer thickness was determined using optical reflectance and the nucleation density was determined using atomic force microscopy (AFM) and Nomarski microscopy. Dislocation density was measured using Xray diffraction and AFM after coating the surface with silicon nitride to delineate all dislocation types. The program milestone of producing GaN films with dislocation densities of 1x10 8 cm -2 was met by silicon nitride treatment of annealed sapphire followed by the multiple deposition of a low density of GaN nuclei followed by high temperature GaN growth. Details of this growth process and the underlying science are presented in this final report along with problems encountered in this research and recommendations for future work.

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Transmission Electron Microscopy Investigation of Dislocations in GaN Layer Grown by Facet-Controlled Epitaxial Lateral Overgrowth

Cited by 34 publications

References 6 publications

Microstructure of a‐plane AlN grown on r‐plane sapphire and on patterned AlN templates by metalorganic vapor phase epitaxy

Microstructure of a‐plane AlN grown on r‐plane sapphire and on patterned AlN templates by metalorganic vapor phase epitaxy

Heteroepitaxial Growth of High‐Quality GaN Thin Films on Si Substrates Coated with Self‐Assembled Sub‐micrometer‐sized Silica Balls

Nanostructural engineering of nitride nucleation layers for GaN substrate dislocation reduction.

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