The microstructure of GaN templates and epitaxial lateral overgrown (ELO) films deposited on M-plane sapphire is investigated by transmission electron microscopy. The epitaxial relationship is [1120]sapphire∥[1100]GaN in-plane with a growth plane close to (1122)GaN. The microstructure of the templates is dominated by the presence of basal stacking faults with a density of around 3×105 cm-1. Basal stacking faults are either terminated by partial dislocations or connected by prismatic stacking faults. Perfect dislocations are also observed. ELO films with stripes parallel to [1100]GaN allow us to reduce the density of basal stacking faults in the overgrown regions down to 5×103 cm-1. In these overgrown materials, the density of perfect dislocations is 108 cm-2 while neither partial dislocation nor prismatic stacking faults are observed.

https://iopscience.iop.org/article/10.1143/JJAP.46.4089/pdf

Microstructural Characterization of Semipolar GaN Templates and Epitaxial-Lateral-Overgrown Films Deposited on $M$-Plane Sapphire by Metalorganic Vapor Phase Epitaxy

The effect of ScN interlayer thickness on the defect density of (112¯2) semipolar GaN grown on m-plane sapphire was studied by transmission electron microscopy. The interlayers comprised Sc metal deposited on a GaN seedlayer that was nitrided before GaN overgrowth by metal-organic vapor-phase epitaxy. Both interlayer thicknesses reduced the dislocation density by a factor of 100 to low-108 cm−2. The 8.5 nm interlayer produced regions that were free from basal plane stacking faults (BSF) and dislocations. The overall BSF density here was reduced by a factor of 5, to (6.49±0.07)×104 cm−1, without the need for an ex situ mask patterning step.

Defect reduction in (112¯2) semipolar GaN grown on m-plane sapphire using ScN interlayers

Semipolar (112¯2) GaN films were obtained by epitaxial lateral overgrowth from (112¯2) GaN templates patterned with SiO2 stripes 7 μm wide with 3 μm spacing, oriented along the [11¯00] GaN in-plane direction. The growth conditions were optimized in order to promote a fast growth rate along the +c [0001] direction. The crystal expands both laterally and vertically until a situation where it overgrows the adjacent crystal, thus stopping the propagation of stacking faults and threading dislocations. The growth anisotropy and filtering of defects is observed by cross-sectional scanning electron microscopy and cathodoluminescence. The lowering of defect density is confirmed by x-ray diffraction measurements. The photoluminescence spectrum of the coalesced epitaxial lateral overgrowth of the (112¯2) epilayers exhibits a strong band edge emission and a low emission band at 3.41 eV, assigned to the remaining stacking faults.

Improved semipolar (112¯2) GaN quality using asymmetric lateral epitaxy

Stacking faults blocking process in (1 1 −2 2) semipolar GaN growth on sapphire using asymmetric lateral epitaxy

Heteroepitaxial nonpolar and semipolar III-nitride films contain numerous structural defects which prevent their use for the development of efficient optoelectronic devices. After a description of the microstructure of such films, this paper reviews the different techniques which have been developed to reduce the densities of the different types of defects. The choice of a well-adapted substrate is discussed. The effect of the introduction of an interlayer is reported. Then, techniques based on the introduction of a 3D growth stage are evaluated. Finally, the original methods based on the growth on inclined facets are described and assessed.

https://iopscience.iop.org/article/10.1088/0268-1242/27/2/024004/pdf

Defect reduction methods for III-nitride heteroepitaxial films grown along nonpolar and semipolar orientations

New conditions for one-step ELO were implemented to grow coalesced (1120) non-polar and (1122) semi-polar GaN layers starting, respectively, from R- and M-plane sapphire A great part of the stacking faults (SFs) and dislocations are filtrated resulting in GaN material with better structural and optical properties In the ELO-like (1120) and (1122) films, the near band edge emission dominates photoluminescence spectra and is in the range 345-348 eV depending on lattice deformation The strongest emission is met for the semi-polar (1122) ELO When mask stripes are not normal to the c-axis, a singular ELO is developed with inclined coalescence facets However, in this case, SFs overgrow above the mask and so lead to poor optical properties, dominated by SF and dislocation related peaks In any case, the internal electric field reduction in (Al,Ga)N/GaN non- or semi-polar quantum-wells stacks is better viewed when the heterostructures are grown on ELO with stripes normal to the c-axis

Reduction of stacking faults in (11$ \bar 2 $0) and (11$ \bar 2 $2) GaN films by ELO techniques and benefit on GaN wells emission

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Reduction of stacking faults in (11$ \bar 2 $0) and (11$ \bar 2 $2) GaN films by ELO techniques and benefit on GaN wells emission