Periodic composition modulations in InGaN epitaxial layers

Abstract

InGaN epitaxial layers grown by metalorganic chemical vapor deposition were investigated in order to understand the occurrence of composition modulations in the GaN–InN system. The In contents of the samples were determined to be x=0.21 and 0.31. Transmission electron microscopy was performed on [0001], [101̄0], and [112̄0] zone-axis specimens. Plan-view images display a domain structure, representing regions in which the directions of the modulations differ. Intersections between domains occur in 〈101̄0〉, and 〈112̄0〉, and other directions. Satellite spots appear in selected-area diffraction patterns. These observations can be explained by diffraction effects resulting from periodic composition modulations. An equation was derived relating the spacing between the satellites and the reflections to the wavelength of the modulations in the wurtzite structure. The sample with x=0.21 had a wavelength of λ=3.1±1.3 nm and the one with x=0.31 had λ=3.2±1.3 nm. Since Young’s modulus is isotropic in the (0001) plane, no particular direction is favored for the modulations based on strain energy considerations. This result is consistent with the observation of the variously oriented domains and satellites.

Compositional Modulation in InxGa1-xN

“…Many ternary and quaternary alloys show either CuPt-type ordering on particular crystallographic planes like in GaInP alloys [17] or compositional ordering [5][6][7][8][9][10][11][12][13]18]. In most cases, the compositional modulation was related to spinodal decomposition driven by asymmetries in the elastic coefficients and phases with different compositions have been formed [5][6][7][8][9].…”

“…In most cases, the compositional modulation was related to spinodal decomposition driven by asymmetries in the elastic coefficients and phases with different compositions have been formed [5][6][7][8][9]. There were also reports on compositional modulation developed on the surface during epitaxial growth, which resulted in a growth of columnar structures with nodules oriented along <100> or <010> directions [12].…”

High-Resolution Electron Microscopy of Semiconductor Heterostructures and Nanostructures

“…In this case, being the nitride layers of good quality, sharp diffraction spots associated with the substrate materials together with a unique set coming from a single crystalline ternary or quaternary It is well known that the low miscibility of binary compounds, especially when using InN, often leads to phase separation effects. Contrasts associated with these effects have been reported by means of DCTEM and SAED for ternary and quaternary alloys, for example, in extensive studies made by Prof. Mahajan's group in the last decade [131][132][133][134][135][136][137].…”

Relation Between Structural and Optical Properties of InN and InxGa1−xN Thin Films

“…In-containing nitrides are very important for application in devices but the large size difference between Ga and In atoms can lead to a spinodal decompositions. Both theoretical and experimental evidences were reported [5,6].…”