Cubic GaN on Nanopatterned 3C-SiC/Si (001) Substrates

Crystal Growth & Design

Peterson

Jiang

et al. 2019

The elastic properties of the cubic (c-) phase GaN confined in a nanoscale one-dimensional (1D) v-grooved Si(001) substrate are investigated. Along a ∼900 nm-wide v-groove formed with two facing Si(111)-type facets, submicrometer-wide c-GaN is achieved by the hexagonal-to c-phase (h−c) transition from the h-GaN which plays the role of an interlayer in its epitaxy on Si. The resulting nonplanar stack of c-GaN/h-GaN on Si has complicated stress distribution. This work focuses on the elastic properties the c-GaN, which are critically affected by its low dimensionality, and presents experimental evidence for it with an analytical stress modeling. A reciprocal lattice map reveals that the c-GaN in each groove consists of several micrometer-long single crystals which are microscopically tilted from each other in their serial coalescence, as its unit structures. The corresponding micrometer-scale lateral correlation length, d c , results from the h−c transition that is interrupted by the groove imperfections generated in fabrication and the stress fluctuation in the misoriented h-GaN interlayer. The modeling suggests that d c is long enough to induce the tensile stress, dominating with the longitudinal strain parallel to the groove which is ∼2.5× the transverse strain, and the c-GaN can be regarded as a serial array of a quasi-1D unit structures which retain such anisotropic stress resulting from their geometrical shape. The Poisson ratio of the c-GaN in <110> is ∼0.21, close to 0.26 from a theoretical prediction. The variation of the c-phase bandgap under the given tensile stress is addressed.

Section: ■ Results and Discussionsupporting

confidence: 74%

Elastic Variation of Quasi-One-Dimensional Cubic-Phase GaN at Nanoscale

Crystal Growth & Design

Peterson

Jiang

et al. 2019

“…Initial stage of cubic GaN for heterophase epitaxial growth induced on nanoscale v-grooved Si(001) in metal-organic vaporphase epitaxy S C Lee 1,5 , Y-B Jiang 2 , M Durniak 3 , C Wetzel 3,4 and S R J Brueck 1 For light emitting diodes (LEDs), the (100) surface in the cubic (c-) phase of III-N compound semiconductors is a nonpolar facet that does not exhibit the piezoelectric effects and impacts the efficiency of emission by removing the degradation associated with them [1]. However, the c-phase III-N is difficult to grow since it is energetically unfavorable compared with the h-phase [2].…”

mentioning

confidence: 99%

Initial stage of cubic GaN for heterophase epitaxial growth induced on nanoscale v-grooved Si(001) in metal-organic vapor-phase epitaxy

Jiang²,

Durniak³

et al. 2018

Nanotechnology

The initial stages of the nucleation of cubic (c-) GaN in heterophase epitaxy on a Si v-groove are investigated. Growth of GaN on a nanoscale {111}-faceted v-groove fabricated into a Si(001) substrate proceeds in the hexagonal (h-) phase that induces a secondary v-groove replicating the substrate topography with two opposing {0001} facets. The secondary v-groove is then orientationally mismatched at the junction of the h-GaN facets (h-h junction) resulting in structural instability. This instability is relieved either by the formation of voids that reduce the actual junction area or by the transition to c-phase (h-c transition) suppressing further extension of the h-h junction. The distribution of voids that is locally affected by the island growth mode of h-GaN on Si(111) and the imperfection in the groove geometry impacts the initial stage of heterophase epitaxy. Primarily, The h-c transition is observed as a non-local phenomenon; it occurs homogeneously and simultaneously along the bottom of the entire secondary groove and forms a one-dimensional (1D) seed layer except for some interruptions where the h-h junction is defected by gaps or incomplete voids. Between these interruptions, epitaxy retains a single crystal but results in a series of c-GaN nanodots on the seed layer with large fluctuation in size and spacing. The adatom incorporation observed in this heterophase epitaxy is a 1D analog to the wetting of a substrate followed by the self-assembly in conventional quantum dot epitaxy. The surface morphology of the c-GaN nanodots is governed by the faceting mostly composed of (001)and (11n)-orientations and the roughening between these facets that ultimately affect the morphology of the final top surface of the c-III-N. The interruptions interfere with the homogeneity of the h-c transition and can cause antiphase defects and mosaicity. Based on experimental results, a solution to improve these issues is proposed.

“…Therefore, a stacking fault in zincblende GaN has the same stacking sequence as the wurtzite structure, and is thought to act as nucleation sites for wurtzite inclusions. The presence of wurtzite inclusions and stacking faults has been found to be correlated by Kemper et al [48] and Martinez-Guerrero et al [32], with the wurtzite inclusions nucleating on the {111} planes.…”

Section: Zincblende Gan Growth Methodsmentioning

confidence: 88%

Cubic zincblende gallium nitride for green-wavelength light-emitting diodes

Materials Science and Technology

2017

Gallium nitride (GaN)-based light-emitting diodes (LEDs) are highly energy efficient and their widespread usage in lighting can induce significant worldwide electricity savings. To achieve white and colour-tuneable lighting, the mixing of light from red-, blue- and green-wavelength LEDs is desired. At present, the efficiency of green-wavelength LEDs is only about half of that of red- and blue-wavelength LEDs, which is also known as the ‘green gap’ problem. Cubic zincblende GaN has the potential to bridge the ‘green gap’ due to the theoretical absence of internal electric fields that plague the commonly used c-plane hexagonal wurtzite structure. This review first looks at the various methods of achieving metastable zincblende GaN, and examines the crystal defects present. Then the different components towards a full zincblende GaN LED structure, including p- and n-type doping, zincblende InGaN and AlGaN on GaN heterostructures, together with the problems that need to be overcome to achieve green-wavelength emissions are reviewed. This review was submitted as part of the 2017 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining run by the Editorial Board of MST. Sponsorship of the prize by TWI Ltd is gratefully acknowledged