Misfit Dislocation Generation in InGaN Epilayers on Free-Standing GaN

Abstract

We have found that, in the absence of threading dislocations in In x Ga 1Àx N/GaN heterostructures, coherent generation of misfit dislocations occurs for x > 0:11 in $100-nm-thick epilayers. We focus this report on In 0:17 Ga 0:83 N grown on a lowdefect-density GaN free-standing substrate (with 1.9% lattice mismatch). A diffraction contrast analysis carried out in the transmission electron microscope showed straight line defects with Burgers vectors 2/3 h11 " 2 20i (i.e., 2a, where a is the hexagonal plane lattice parameter), which extended many micrometers approximately along h1 " 1 100i directions and with an average lateral spacing of 90 nm. Although these defects were complex and mostly sessile, evidence was found that they can dissociate into glissile misfit dislocations with Burgers vectors of 1/3 h11 " 2 20i. It is proposed that the defects are generated by a punch-out mechanism involving slip on inclined prismatic planes. The properties of these defects and their role in relieving misfit strains are discussed.

Defects, strain relaxation, and compositional grading in high indium content InGaN epilayers grown by molecular beam epitaxy

“…5 illustrates such an image from sample B. Three arrays of straight edge-type misfit dislocations aligned along the crystallographically equivalent h1 100i directions were observed, revealing the operation of pyramidal slip systems during the formation of the SQL, 47 and thus confirming the postulate made by Wang et al 33 On occasion, dissociations of these misfit dislocations were observed, as illustrated by black arrows in Fig. 5, showing that they may also bear 2a Burgers vector components.…”

“…5, showing that they may also bear 2a Burgers vector components. 47 The average spacing of the misfit dislocations in sample B was determined at p ¼ 292 nm. Using the equation f ¼ Àb/p, where b is the magnitude of the Burgers vector, the plastic strain relaxation of the SQL was found equal to À0.11% corresponding to a lattice constant of a ¼ 0.3192 nm for s-InGaN.…”

Control of Defects in Aluminum Gallium Nitride ((Al)GaN) Films on Grown Aluminum Nitride (AlN) Substrates

“…Liu et al (37) attributed the relatively small reduction in the amount of plastic strain in the growth of InGaN on GaN to the difficulty in forming these dislocations. Also the number of pyramidal dislocations is greatly reduced when growth planes other than the plane are exposed for growth either by etching the GaN substrate to form etch pits (38) or by creating mesas (39). This is attributed to basal plane dislocations with smaller critical resolved shear stresses being created instead to relieve the plastic strain now that there are shear stresses on the basal plane.…”

Pyramidal dislocation induced strain relaxation in hexagonal structured InGaN/AlGaN/GaN multilayer

“…2,3,[9][10][11][12][13][14][15][16][17][18][19] The strain relaxation is generally conducted by introducing misfit dislocation from free surface to interface and dislocation bowing mechanism. A variety of deformation mechanisms have been purposed to achieve superior mechanical properties by designing multilayer system with different lattice structures.…”

“…For example, in hexagonal GaN based multilayers, which are widely used semiconductor materials, misfit dislocations are not commonly observed as in cubic GaAs based heterostructures. 17,18,27 This is due to the special slip system in hexagonal-lattice crystals, where the primary slip system ({0001}<11-20>) had no shear component from the misfit stress for epitaxial growths on the (0001) plane. Although the secondary slip dislocations ({11-22}<11-23>) could be activated by nonzero effective shear stress, their large Burgers vectors (b ¼ 1/3 [11][12][13][14][15][16][17][18][19][20][21][22][23]) make them hard to initiate.…”