Classic and novel methods of dislocation reduction in heteroepitaxial nitride layers

Abstract

Due to the lack of commercially available large size native substrates, reduction of threading dislocations remains one of the main challenges of group III-nitride based technology. This paper reviews major methods aimed at producing high-quality heteroepitaxial nitride films with reduced densities of dislocations. Methods such as, incorporation of buffer layers, substrate nitridation, interlayer insertion, silaneammonia treatment, lateral overgrowth and growth of thick nitride layers are reviewed. Advantages and drawbacks of these methods are discussed and compared.Introduction One of the main problems of the group III nitride-based technology is the lack of commercially available large-size native substrates. Sapphire or 6H-SiC substrates, are typically chosen for most nitride-based applications. These substrates however, are poorly matched to nitride films. There is, for example, a lattice mismatch of 16 and 13 % between c-plane sapphire substrates and GaN and AlN layers, respectively. As a result, the growth of nitride films directly on such substrates leads to the formation of three-dimensional (3D) islands [1,2]. In the initial stage of the growth, these slightly twisted/tilted islands coalesce leading to the formation of threading dislocations. Also, threading dislocations are formed to reduce the biaxial compressive strains [3,4] resulting from the lattice mismatch during the growth, as well as from the mismatch in thermal expansion coefficient between the layer and the substrate during the post-growth cooling. As a consequence high densities of threading dislocations, usually in the range of 10

Analysis of threading dislocations in void shape controlled GaN re-grown on hexagonally patterned mask-less GaN

“…These techniques usually involve blocking of the dislocations using a suitable mask, controlling the growth direction of particular facets or a combination of both (for a detailed review see Refs. [15,16]). …”

A Chemical Solution Approach to Epitaxial Metal Nitride Thin Films

“…In general, the difficulty in the heteroepitaxial growth of such films lies in the large mismatches in either lattice parameters or thermal-expansion coefficients between the film and the substrate. [32] Nitride films with rough surface morphologies and high densities of defects are often observed. [32] All of the above-reported deposition routes to epitaxial nitride films have the common feature of requiring vacuum systems.…”

Extended defects in bulk GaN and III-nitrides grown on this substrate

“…X-ray studies using the (0 0 4) Cu K a reflection show narrow X-ray rocking curve with full width at half maximum in the range 20-30-arcsec [18]. The dislocation density in these crystals is very low and does not exceed 10 2 cm À 2 [3], whereas the density of dislocations grown on foreign substrates is as high as 10 10 cm À 2 close to the interface with the buffer layer and decreasing with the thickness of the layer to about 10 6 cm À 2 [16,17] near the surface. The roughness of both surfaces of the platelets is different.…”

“…Since different devices such as light emitting diodes (LEDs) and laser diodes (LDs) require the growth of ternary layers on these substrates, it will be shown how the structural quality of the layers changes depending on the substrate surface preparation and composition of the layer. These results will be compared to the layers grown heteroepitaxially on foreign GaN/Al 2 O 3 substrates grown by HVPE, where the lattice parameter and thermal expansion coefficient mismatch between the substrate and the epitaxial layer leads to high defect densities in these layers [16,17].…”