Transmission electron microscopy of defects in GaN films formed by epitaxial lateral overgrowth

Sakai, Akira; Sunakawa, Hajime; Usui, Akira

doi:10.1063/1.121907

Cited by 200 publications

(110 citation statements)

References 4 publications

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“…19 Also, the island boundary regions contained a large number of dislocations. 5,20 In addition, the facet edges in our AlGaN epitaxial layers tend to be Ga-rich regions, and thus a local strain field is introduced at the coalescence boundary. Therefore, it is likely that impurities and/or point defects are concentrated locally and exhibit peculiar properties.…”

Section: Resultsmentioning

confidence: 99%

Inhomogeneous distribution of defect-related emission in Si-doped AlGaN epitaxial layers with different Al content and Si concentration

Kurai¹,

Ushijima²,

Miyake³

et al. 2014

Journal of Applied Physics

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The spatial distribution of luminescence in Si-doped AlGaN epitaxial layers that differ in Al content and Si concentration has been studied by cathodoluminescence (CL) mapping in combination with scanning electron microscopy. The density of surface hillocks increased with decreasing Al content and with increasing Si concentration. The mechanisms giving rise to those hillocks are likely different. The hillocks induced surface roughening, and the compositional fluctuation and local donor-acceptor-pair (DAP) emission at hillock edges in AlGaN epitaxial layers were enhanced irrespective of the origin of the hillocks. The intensity of local DAP emission was related to Si concentration, as well as to hillock density. CL observation revealed that DAP emission areas were present inside the samples and were likely related to dislocations concentrated at hillock edges. Possible candidates for acceptors in the observed DAP emission that are closely related in terms of both Si concentration and hillock edges with large deformations are a V III -Si III complex and Si N , which are unfavorable in ordinary III-nitrides. V C 2014 AIP Publishing LLC.

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Section: Resultsmentioning

confidence: 99%

Inhomogeneous distribution of defect-related emission in Si-doped AlGaN epitaxial layers with different Al content and Si concentration

Kurai¹,

Ushijima²,

Miyake³

et al. 2014

Journal of Applied Physics

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“…Although the ELO process using hydrogen ambient reduces the dislocation density of the GaN layer, it introduces the anisotropic crystallographic tilting. The anisotropic tilting is drastically enhanced in nitrogen ambient, but the tilt angle is smaller than that reported by Sakai et al [15]. The mechanism of this phenomenon is under study.…”

Section: Resultsmentioning

confidence: 50%

Hydrogen and Nitrogen Ambient Effects on Epitaxial Lateral Overgrowth (ELO) of GaN VIA Metalorganic Vapor-Phase Epitaxy (Movpe)

Tadatomo

Ohuchi

Okagawa

et al. 1999

MRS Internet j. nitride semicond. res.

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Ambient gas effect on the epitaxial lateral overgrowth (ELO) of GaN via metalorganic vapor-phase epitaxy (MOVPE) on a MOVPE-grown GaN (0001) / sapphire (0001) substrate with a SiO 2 stripe mask has been studied by means of field-emission scanning electron microscopy (SEM) and highresolution X-ray diffraction (XRD) analysis. Different ambient gases of nitrogen, hydrogen and their mixture (mixture ratio, hydrogen : nitrogen = 1 : 1) affect the lateral overgrowth rate, the surface morphology and the crystalline tilting of ELO-GaN layers. XRD revealed that the ELO-GaN layer on the SiO 2 mask aligned along the <1 -100> direction exhibited anisotropic crystalline tilting toward <11 -2 0>. For ELO-GaN growth in nitrogen ambient, the growth rate of the (0001) facet decreases, the lateral overgrowth rate increases and the tilting of the ELO-GaN layer increases, while no smooth surface is obtained, in comparison with ELO-GaN growth in hydrogen ambient. For the mixture ambient, a smooth surface with a fast lateral overgrowth rate is achieved and the dislocation density is not more than 10 7 cm -2 , which is comparable to that in hydrogen ambient. IntroductionRecently, high-performance optical devices such as light-emitting diodes (LEDs) and laser diodes (LDs) in green and ultraviolet regions have been developed using GaN, AlGaN and InGaN compound semiconductors [1,2]. These GaN-related devices are usually fabricated on a sapphire substrate, because there is no large-scale substrate for GaN heteroepitaxial growth. Due to the large differences in lattice constant, thermal expansion coefficient and chemical nature between GaN and sapphire, many threading dislocations are formed from the GaN or AlN buffer layer on the sapphire substrate, and the dislocation density has been reported to be of the order of 10 9 -10 10 cm -2 [3]. Although high-brightness LEDs have been realized in spite of the high dislocation density, the reduction of the dislocation density is desired to improve the performance and reliability of these devices. The epitaxial lateral overgrowth (ELO) technique based on the selective area growth (SAG) has recently attracted considerable attention, since the fabrication of blue-violet laser diodes on the ELO-GaN layer using this technique resulted in the achievement of a long lifetime of more than 10,000 hours [4].The SAG in MOVPE on GaN/sapphire and AlGaN/sapphire with SiO 2 stripe patterns was published for the first time in 1994 by Kato et al. [5], followed by that on GaN/sapphire [6]. Intensive studies on SAG have revealed that the ELO effectively reduces the dislocation density [4,[7][8][9][10][11]. The crystalline properties and the growth mechanism of ELO-GaN can be affected by mask patterns such as stripe direction [10][11][12][13] and growth conditions such as growth temperature [10], source gases [10], growth pressure and ambient gas. However, the effects of ambient gas remain unclear. We investigate the effects of hydrogen gas, nitrogen gas and their mixture in an atmospheric MOVPE on ELO-GaN.

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“…This general behavior is also found for dislocations initially oriented along the [0001] growth direction if inclined facets appear during growth of GaN epitaxial layers. The dislocations then bend toward the inclined facet, [19][20][21]23,25,26,65 in order to minimize the line energy by shortening its length. Note, the dislocations in the cleaved samples likely do not reach their equilibrium line directions after cleavage at room temperature.…”

Section: Determination Of the Depth Of The Dislocation Corementioning

confidence: 99%

“…18 Therefore, the need to reduce the dislocation concentrations has led to growth schemes, where the dislocation lines are bent off the growth direction. [19][20][21][22][23][24][25][26] Hence, most dislocations are not present in their original line direction and may thus change their electronic properties. Therefore, it is particularly relevant to be able to identify the line direction of the dislocation cores.…”

Section: Introductionmentioning

confidence: 99%

Tracking the subsurface path of dislocations in GaN using scanning tunneling microscopy

Weidlich

Schnedler

Portz

et al. 2015

Journal of Applied Physics

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A methodology for the determination of the subsurface line direction of dislocations using scanning tunneling microscopy (STM) images is presented. The depth of the dislocation core is derived from an analysis of the displacement field measured by STM. The methodology is illustrated for dislocations at GaN(10 10) cleavage surfaces. It is found that the dislocation line bends toward the surface, changing from predominantly edge-type to more screw-type character, when approaching the intersection point. Simultaneously, the total displacement detectable at the surface increases due to a preferred relaxation towards the surface. V C 2015 AIP Publishing LLC.

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Transmission electron microscopy of defects in GaN films formed by epitaxial lateral overgrowth

Cited by 200 publications

References 4 publications

Inhomogeneous distribution of defect-related emission in Si-doped AlGaN epitaxial layers with different Al content and Si concentration

Inhomogeneous distribution of defect-related emission in Si-doped AlGaN epitaxial layers with different Al content and Si concentration

Hydrogen and Nitrogen Ambient Effects on Epitaxial Lateral Overgrowth (ELO) of GaN VIA Metalorganic Vapor-Phase Epitaxy (Movpe)

Tracking the subsurface path of dislocations in GaN using scanning tunneling microscopy

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