Defect-selective etching of GaN in a modified molten bases system

Kamler, G.; Weyher, J.L.; Grzegory, I.; Jezierska, E.; Wosiński, T.

doi:10.1016/s0022-0248(02)01786-4

Cited by 95 publications

(86 citation statements)

References 7 publications

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“…To check the structural quality of all epilayers, the samples have been examined by X-ray rocking curve mode using a Bruker D8 Discovery X-ray diffractometer with a Cu target (λ = 1.54060 Å) and a 4-bounce monochromator Ge (022). From all samples, small pieces were cut to perform defect-selective etching using molten eutectic mixture of KOH-NaOH (E) with 10% of MgO powder (E + M) [8]. Additionally, some samples were also subjected to photo-etching in a stirred KOH solution (0.004 molar) at room temperature using UV illumination provided by a 450 W Xe lamp.…”

Section: Methodsmentioning

confidence: 99%

Defect formation in GaN grown on vicinal 4H‐SiC (0001) substrates

Rudziński¹,

Jezierska

Weyher

et al. 2007

Physica Status Solidi (a)

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We report a comparative study of wurtzite GaN epilayers prepared by Metal Organic Chemical Vapor Deposition on 4H-SiC substrates of orientation vicinal to the (0001) (misorientation 0°, 3.4°, and 8°). Structural analysis using X-ray diffraction, defect-selective etching methods, and (High Resolution-) Transmission Electron Microscopy provides direct evidence for a higher number of defects in GaN epilayers grown on the 8° misoriented substrate compared to the 3.4° and 0° misoriented substrates. We found strong differences in morphology of the GaN epilayers and in type and density of the defects formed during growth on both vicinal and nominally exact oriented SiC substrates. The formation of clusters of defects and the non-uniform distribution of strain, resulting in preferential cracking of the GaN films along the [1120] direction, are both results of growth on misoriented substrates. Based on experimental results, the growth mechanism is discussed and a model explaining the defect formation is proposed.

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Section: Methodsmentioning

confidence: 99%

Defect formation in GaN grown on vicinal 4H‐SiC (0001) substrates

Rudziński¹,

Jezierska

Weyher

et al. 2007

Physica Status Solidi (a)

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“…As a rule orthodox etching in molten salts (KOH [9], eutectic alloy of KOH-NaOH=E etch [11] and E+MgO=E+M etch [13]) and hot acids [11,14] results in formation of pits of different sizes. The attempts to attribute the size of pits to the type of dislocations showed unambiguously that the largest pits are formed on nano-pipes, i.e.…”

Section: Introductionmentioning

confidence: 99%

“…Different morphologies of pits formed on edge, mixed and screw dislocations were reported after etching of GaN in HCl at 600 °C [16], while after etching in molten KOH Shiojima [12] found larger pits on mixed and smaller ones on edge dislocations. Etching in modified E+M etch of MOCVD-grown hetero-epitaxial GaN layers lead to the conclusion that the largest pits are formed on nano-pipes and the smallest on edge dislocations [13]. It was tentatively concluded that the size of pits from the largest to the smallest follows the size of Burgers vectors of dislocations in GaN (nano-pipes, screw, mixed, edge, with the exception for the screw and mixed defects) [17].…”

Section: Introductionmentioning

confidence: 99%

Orthodox etching of HVPE-grown GaN

Weyher

Lazar

Macht

et al. 2007

Journal of Crystal Growth

116

103

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Orthodox etching of HVPE-grown GaN in molten eutectic of KOH + NaOH (E etch) and in hot sulfuric and phosphoric acids (HH etch) is discussed in detail. Three size grades of pits are formed by the preferential E etching at the outcrops of threading dislocations on the Ga-polar surface of GaN. Using transmission electron microscopy (TEM) as the calibration tool it is shown that the largest pits are formed on screw, intermediate on mixed and the smallest on edge dislocations. This sequence of size does not follow the sequence of the Burgers values (and thus the magnitude of the elastic energy) of corresponding dislocations. This discrepancy is explained taking into account the effect of decoration of dislocations, the degree of which is expected to be different depending on the lattice deformation around the dislocations, i.e. on the edge component of the Burgers vector. It is argued that the large scatter of optimal etching temperatures required for revealing all three types of dislocations in HVPE-grown samples from different sources also depends upon the energetic status of dislocations. The role of kinetics for reliability of etching in both etches is discussed and the way of optimization of the etching parameters is shown.

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“…% MgO was used to increase the size of the dislocations. 23 The enlarged pits were imaged in plan-view with a scanning electron microscope and counted over an area of $100 lm 2 to determine the dislocation density. The threading dislocation density in AlN was estimated from plan-view transmission electron microscope (TEM) images.…”

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confidence: 99%

Layer-by-layer thermal conductivities of the Group III nitride films in blue/green light emitting diodes

Huang

Liu

et al. 2012

Applied Physics Letters

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Thermal conductivities (k) of the individual layers of a GaN-based light emitting diode (LED) were measured along [0001] using the 3-omega method from 100-400 K. Base layers of AlN, GaN, and InGaN, grown by organometallic vapor phase epitaxy on SiC, have effective k much lower than bulk values. The 100 nm thick AlN layer has k ¼ 0.93 6 0.16 W/mK at 300 K, which is suppressed >100 times relative to bulk AlN. Transmission electron microscope images revealed high dislocation densities (4 Â 10 10 cm À2 ) within AlN and a severely defective AlN-SiC interface that cause additional phonon scattering. Resultant thermal resistances degrade LED performance and lifetime making layer-by-layer k, a critical design metric for LEDs. More than 20% of electricity in the United States is consumed by lighting. Solid-state light emitting diodes (LEDs) hold considerable potential to be more efficient and effective sources of artificial light than incandescent and fluorescent technologies. 1 Group III nitride-based blue and green LEDs are currently being developed for this purpose. Device architectures consist of light-emitting multiple quantum wells (MQWs) supported by base layers of aluminum nitride (AlN), gallium nitride (GaN), and indium gallium nitride (InGaN). The MQW itself is a periodic structure composed of alternating InGaN wells and GaN barriers.Heat generation and removal in the LED are complicated by multiple interfaces, causing high operating temperatures that degrade efficiency, shift the emission spectrum, and reduce the lifetime of LEDs. 2 Prior experimental investigations of bulk GaN and AlN have shown that thermal transport is phonon-dominated. [3][4][5][6] Previous thin film studies have been (i) based on ideal films with low defect concentrations that are unrepresentative of LED grade films 3,7 or (ii) focused on high electron mobility transistors (HEMTs), rather than LED architectures. [8][9][10] Neither submicron GaN films nor real nitride based LED devices have been investigated.Studies of Si and other thin films have demonstrated that thermal conductivity is greatly reduced when the thickness of the film or the defect spacing is less than the intrinsic mean free path of the phonons. 5,11,12 Nitride based LED structures are fabricated from multiple layers of thin films ranging from 3 nm to 100 nm in thickness; whereas, the spectrum-average phonon mean free path in GaN at 300 K is $100 nm, 13 and the longest phonon mean free paths in the spectrum are much greater. 14 To achieve economic viability, the nitride films are grown by organometallic vapor phase epitaxy (OMVPE) on foreign substrates, including SiC, sapphire, and Si. Mismatched lattice constants at the filmsubstrate interface create high densities of atomic and line defects, the latter of which that extend throughout the device as a source of phonon scattering. Given these considerations, this paper reports layer-by-layer experimental measurements of thermal conductivity in real nitride based LED architectures grown on [0001]-oriented SiC substrates. Th...

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Defect-selective etching of GaN in a modified molten bases system

Cited by 95 publications

References 7 publications

Defect formation in GaN grown on vicinal 4H‐SiC (0001) substrates

Defect formation in GaN grown on vicinal 4H‐SiC (0001) substrates

Orthodox etching of HVPE-grown GaN

Layer-by-layer thermal conductivities of the Group III nitride films in blue/green light emitting diodes

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