Intrinsic degradation mechanism of nearly lattice-matched InAlN layers grown on GaN substrates

Abstract

Thanks toits high refractive index contrast, band gap and polarization mismatch compared to GaN, In 0.17 Al 0.83 N layers lattice-matched to GaN are an attractive solution for applications such as distributed Bragg reflectors, ultraviolet light-emitting diodes, orhigh electron mobility transistors. In order to study the structural degradation mechanism of InAlN layers with increasing thickness, we performed metalorganic vapor phase epitaxy of InAlN layers of thicknesses ranging from 2 to 500 nm, on free-standing (0001) GaN substrates with a low density of threading dislocations, for In compositions of 13.5% (layers under tensile strain), and 19.7%(layers under compressive strain). In both cases, a surface morphology with hillocks isinitially observed, followed by the appearance of V-defects. We propose that those hillocks arise due to kinetic roughening, and that V-defects subsequently appear beyonda critical hillock size. It is seen that the critical thickness for the appearance of V-defects increases together with the surface diffusion length either by increasing the temperature or the In flux because of asurfactant effect.In thick InAlN layers, a better (worse) In incorporation occurring on the concave (convex) shape surfaces of the V-defects is observed leading to a top phase-separated InAlN layer lying on the initial homogeneous InAlN layerafterV-defects coalescence.It is suggested that similar mechanisms could be responsible for the degradation of thick InGaN layers.

Optical absorption edge broadening in thick InGaN layers: Random alloy atomic disorder and growth mode induced fluctuations

“…Note that the latter aspect has also been shown to be especially dramatic in the case of the InAlN alloy. 38 Furthermore, strain fluctuations due to the large lattice-mismatch between InN and GaN will most likely affect more deeply the local indium incorporation with the increasing targeted indium content, hence further enhancing alloy disorder.…”

Growth of AlInN/GaN distributed Bragg reflectors with improved interface quality

“…1(a). With an increasing film thickness, these V-pits become larger until coalescence leading to a degraded, phase separated, and rough film [9]. It has been shown, that the formation of these pits is not necessarily linked to threading dislocations, since they also appear when AlInN films are grown on high quality free-standing GaN substrates.…”

“…In the last years large efforts were made to find the optimum set of growth parameters and the material quality was increasingly improved. Nevertheless, the thickness for smooth single-phase AlInN films is still limited to about 200 nm [9]. For thicker films a strong roughening and phase separation is observed.…”

Importance of growth temperature on achieving lattice-matched and strained InAlN/GaN heterostructure by plasma-assisted molecular beam epitaxy

“…The growth of GaN, AlN and InAlN surfaces were monitored by in situ reflection-high energy electron diffraction (RHEED) along the [11][12][13][14][15][16][17][18][19][20] azimuth. Upon nucleation, the bright 1 × 1 RHEED pattern remained streaky as that of GaN layer for lattice matched InAlN.…”

“…9 distributed Bragg reflectors for use in vertical cavity surface emitting lasers 10 and structural defects and degradation mechanism of thick nearly lattice matched InAlN layers. 11 In this report, we intend to investigate the temperature induced structural evolutions, indium compositional variations and the electrical transport properties of strained and nearly lattice matched InAlN layers to GaN. A thin InAlN/GaN heterostructure experiences cracks owing to tensile strain at low very In composition of ∼ 4% and nearly strain free mirror like smooth features with no visible defects for close lattice matched (∼16%) conditions were observed, besides accumulation of indium clusters for higher Indium composition viz.…”