Evolution of stratification in high-alloy content InGaN epilayers grown on (0001) AlN

Abstract

The structural properties of In xGa1− xN epilayers, deposited on (0001) AlN templates by plasma-assisted molecular beam epitaxy, were studied by transmission electron microscopy and Raman spectroscopy, as a function of growth temperature. Single phase films with high indium content and well-ordered heteroepitaxial interfaces were attained at lower temperatures. Delayed plastic relaxation resulted in the structural stratification of high-temperature films due to the compositional pulling. Such films relaxed by a stacking fault mechanism, contrary to low temperature ones that exhibited relaxation by misfit dislocations. Despite the higher defect content of the former, their phonon mean free path was also higher, showing that alloying-induced fluctuations of the periodic potential constitute a more critical parameter. Cubic interfacial zones were suppressed at lower growth temperatures. This is part of a thematic issue on Nanoscale Materials Characterisation and Modeling by Advances Microscopy Methods - EUROMAT.

Stacking Fault Manifolds and Structural Configurations of Partial Dislocations in InGaN Epilayers

“…HRTEM observations were performed in InGaN epilayers deposited on (0001) GaN and AlN templates by plasma-assisted molecular beam epitaxy, as detailed elsewhere. [19,20,51] The samples were grown at different temperatures, from 475 up to 590 C, under slightly metal-rich conditions. The indium content of the epilayers increased with decreasing growth temperature, starting from 12% and reaching 48%.…”

“…Cross-sectional HRTEM observations showed that, in such films, extensive introduction of BSFs is associated with gradual strain relaxation imposed by the compositional pulling effect. [19,20] The introduction of BSFs was prominent in the compositional range between 18% and 36% indium content. However, the contribution of BSFs to strain relaxation was not elucidated.…”

“…[17] The dislocation issue is particularly important in high In-content InGaN epilayers that are promising for photovoltaics, sensors, and terahertz applications. [18][19][20] Basal stacking faults (BSFs) and their associated partial dislocations (PDs) constitute an important class of defects for III-nitride semiconductors. They can be introduced in high densities in InGaN heteroepitaxy due to double positioning or local deviations from stoichiometry.…”

“…They can be introduced in high densities in InGaN heteroepitaxy due to double positioning or local deviations from stoichiometry. [19][20][21] Such BSFs are usually intrinsic in character, with the most frequent being the I 1 type, and next in line the I 2 type. [22] BSFs are also dominant defects in nonpolar and semipolar III-nitride epilayers that are technologically utilized to reduce the quantum-confined Stark effect.…”

The heterogeneous nucleation of threading dislocations on partial dislocations in III-nitride epilayers

“…Such small variations of the indium content when crossing the domains were generally observed but were not systematic. Since the In 0.19 Ga 0.81 N layer was only 12% relaxed through introduction of (a + c) misfit dislocations 15 , the observed changes in the indium content may be attributed to local alloy compositional fluctuations on account of the compositional pulling phenomenon, and not to a strain relaxation process [32][33][34] . Also, we did not find by EELS that the BSFs themselves or the emanating TDs were enriched in indium.…”