Strain Relaxation Mechanisms in AlGaN Epitaxy on AlN Templates

Abstract

Two strain relaxation processes have been observed in AGaN layers grown on thick AlN templates. In Process I, a-type threading dislocations (TDs) with b= 1/3<1120> from the AlN underlayer are inclined away from the [0001] axis toward the <1100> directions when they enter the AlGaN film, forming dislocation line projection perpendicular to the Burger vector. In Process II, a+c-type TDs from the AlN underlayer with Burgers vector of b= 1/3<1123> glide on {0111} planes when they enter the AlGaN film to generate interfacial misfit dislocations lying along the <2110> directions at the AlGaN/AlN interface.

Defect analysis in AlGaN layers on AlN templates obtained by epitaxial lateral overgrowth

“…Considering the atomically smooth surface as well as the low TDD in the ELO-AlN(a) template, this behavior might be explained by strain relaxation in thick Al 0.5 Ga 0.5 N layers through enhanced surface corrugation (transition to threedimensional (3D) growth). A similar effect has been frequently observed in AlGaN layers with increasing Ga content grown on planar AlN [25,26], where increasing compressive strain can be relaxed either through formation of additional dislocations and dislocation inclination (preferably for AlGaN with high Al content [24,27,28]) or through an enhanced surface roughening (preferably for low Al contents [25,26]). It should be emphasized that in our experiment we have applied the same deposition conditions for Al 0.5 Ga 0.5 N growth on both ELO-AlN(a) and ELO-AlN(m) templates.…”

High‐Temperature Annealing of AlGaN

“…Otherwise, AlGaN relaxation can lead to surface roughening and formation of misfit dislocations during growth. [12,13] Misfit dislocations can drastically increase the TDD by bending out of plane. Hence, providing low TDD Al x Ga 1Àx N buffer layers instead of low TDD AlN buffers is desirable for UVA and UVB LEDs.…”

Highly luminescent, high-indium-content InGaN film with uniform composition and full misfit-strain relaxation

“…2,3 In c-plane epitaxy, misfit dislocations may be introduced by glide along the basal plane, 4 by glide along the f11 22gh11 23i slip system, 3 and by bending of dislocations threading from the GaN underlayer. 5 Growth of InGaN films is also affected by compositional instabilities, with predicted spinodal decomposition over a wide range of indium content. 6,7 However, In x Ga 1Àx N films with x 0.25 have been reported to grow without phase separation by molecular beam epitaxy (MBE) in the growth temperature range of 650-675 C. 8 It has also been shown that uniform InGaN layers can be grown at lower temperatures without phase separation over a wide range of indium compositions using metal-modulated epitaxy, 9 a modified MBE technique where the metal flux is periodically modulated to enhance surface adlayer diffusion while the nitrogen flux is kept constant.…”