Improvement of Crystalline Quality of Group III Nitrides on Sapphire Using Low Temperature Interlayers

Amano, Hiroshi; Iwaya, Motoaki; Hayashi, Nobuaki; Kashima, Takayuki; Katsuragawa, Maki; Takeuchi, Tetsuya; Wetzel, Christian; Akasaki, Isamu

doi:10.1557/s1092578300003550

Cited by 40 publications

(44 citation statements)

References 18 publications

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“…by HVPE, many methods are known to reduce the dislocation density and the most often applied are based on masking and lateral overgrowth commonly known as ELOG or LEO [10] and pendeo epitaxy [11,12], all methods involving an ex-situ processing step before growth or after a first buffer layer has been grown. In-situ methods as Al(Ga)N/GaN superlattices [13] or AlN or Si x N y interlayers [14,15] are also suited to reduce the dislocation density without ex-situ processing. Table 1) does, as opposite to GaN on sapphire, induce tensile stress in GaN on silicon resulting in crack formation when cooling.…”

Section: Materials Propertiesmentioning

confidence: 99%

Metalorganic chemical vapor phase epitaxy of gallium‐nitride on silicon

Dadgar

Strittmatter

Bläsing

et al. 2003

phys. stat. sol. (c)

129

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GaN growth on Si is very attractive for low-cost optoelectronics and high-frequency, high-power electronics. It also opens a route towards an integration with Si electronics. Early attempts to grow GaN on Si suffered from large lattice and thermal mismatch and the strong chemical reactivity of Ga and Si at elevated temperatures. The latter problem can be easily solved using gallium-free seed layers as nitrided AlAs and AlN. The key problem for device structure growth on Si is the thermal mismatch leading to cracks for layer thicknesses above 1 µm. Meanwhile, several concepts for strain engineering exist as patterning, Al(Ga)N/GaN superlattices, and low-temperature (LT) AlN interlayers which enable the growth of device-relevant GaN thicknesses. The high dislocation density in the heteropitaxial films can be reduced by several methods which are based on lateral epitaxial overgrowth using ex-situ masking or patterning and by in-situ methods as masking with monolayer thick SiN. With the latter method in combination with strain engineering by LT-AlN interlayers dislocation densities around 109 cm -2 can be achieved for 2.5 µm thick device structures.

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Section: Materials Propertiesmentioning

confidence: 99%

Metalorganic chemical vapor phase epitaxy of gallium‐nitride on silicon

Dadgar

Strittmatter

Bläsing

et al. 2003

phys. stat. sol. (c)

129

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show abstract

“…These cracks, observable in an optical microscope on a ~ mm scale, have been reported to have a potentially dual role in the strain relaxation, through the formation of misfit dislocation on the basal plane [2] in addition to the relaxation caused by the crack itself. Such crack networks can be avoided through the use of a low temperature interlayer of AlN at the AlGaN-GaN interface for example [4], but these methods are not suitable in all cases and can cause an increased threading dislocation density.The above studies have discussed the propagation and relaxation induced by cracks, but none have reported on their nucleation or on the microscopic structural properties for layers below which the gross cracks have been observed. In a previous report [5] we have suggested that the gross cracks may be formed as a result of "microcracks" observed at much lower thicknesses.…”

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confidence: 99%

Crack formation and development in AlGaN/GaN structures

Parbrook

Wang

Whitehead

et al. 2003

phys. stat. sol. (c)

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In the absence of the use of prevention methods, AlGaN layers on GaN are known to form an array of cracks if a critical thickness is exceeded. In this study growth of AlGaN-GaN structures was carried out by metalorganic vapour phase epitaxy using sapphire substrates. Under optical and atomic force microscopy two distinct crack populations have been obseved. In thin, highly strained films an initial high density population of microcracks are found propagating from threading dislocations. This crack array extends as the thickness increases, before contracting with the onset of large cracks whick extend over many mm across the wafer. The formation of the microcrack array is very dependent on the stain in the epilayer and does not follow the classic critical thickness dependence with lattice mismatch. Avoiding stresses high enough to prevent the microcracking phenomenon may be critical in the use of highly tensile strained layers in nitride devices.1 Introduction AlGaN epilayers are critical to the formation of many III-nitride devices. These include laser diodes (LDs), heterojunction field effect transistors (HFETs), ultra-violet emitters, solar blind photodetectors and also intersubband devices. However, the lattice mismatch between AlN and GaN means that AlGaN layers grown on GaN experience a high degree of tensile stress which can lead to the formation of an array cracks over the sample surface [1][2][3]. These cracks, observable in an optical microscope on a ~ mm scale, have been reported to have a potentially dual role in the strain relaxation, through the formation of misfit dislocation on the basal plane [2] in addition to the relaxation caused by the crack itself. Such crack networks can be avoided through the use of a low temperature interlayer of AlN at the AlGaN-GaN interface for example [4], but these methods are not suitable in all cases and can cause an increased threading dislocation density.The above studies have discussed the propagation and relaxation induced by cracks, but none have reported on their nucleation or on the microscopic structural properties for layers below which the gross cracks have been observed. In a previous report [5] we have suggested that the gross cracks may be formed as a result of "microcracks" observed at much lower thicknesses. These microcracks are short, sub-µm in length an hence would not be observable by optical microscopy for example. In this paper evidence is shown that this microcracking phenomenon in thin highly strained AlGaN layers grown on GaN can occur in very thin layers indeed, and that their density rapidly decreases with the onset of "gross" crack formation.

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“…This isolation layer acts either as a trap for possible oxygen contamination, or as a layer that interrupts the highly defective layer near the GaN/sapphire interface. Such isolation layer can also improve the crystalline quality of the sample [14].…”

Section: Discussionmentioning

confidence: 99%