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Strain Relaxation in In(Ga)N/GaN Short Period Superlattices

Vasileiadis, I. G.; Adikimenakis, A.; Dimakis, E.; H├╝bner, R.; Lymperakis, L.; Georgakilas, A.; Karakostas, T.; Komninou, P.; Dimitrakopulos, G. P.

Introduction/Purpose: Short period superlattices (SPSs) comprising ultrathin InGaN/GaN quantum wells (QW) with thicknesses ranging from one to few (0002) monolayers (MLs) are promising for novel applications ranging from band gap engineering in optoelectronic devices to topological insulators. The strain relaxation behavior of a range of samples grown by varying the growth temperatures for the QWs and GaN barriers has been considered.
Methods: In(Ga)N/GaN SPSs were deposited by plasma-assisted molecular beam epitaxy (PAMBE) on c-GaN/Al2O3 templates. Structural characterization was performed by high resolution transmission and scanning transmission electron microscopy (HRTEM/HRSTEM).
Results: Strain relaxation through formation of stacking fault domains was observed with decreasing growth temperature. For the quantification of strain versus composition, peak finding with a recently established approach was implemented. This involves quantification of Z-contrast from HRSTEM observations by comparison with calculated composition-dependent graphs of InxGa1-xN/GaN atomic column intensity ratios obtained from multislice image simulations of energetically relaxed supercells under the frozen lattice approximation. Energetical relaxation was performed by molecular dynamics using an empirical interatomic potential, considering the ordered, disordered, and island models of QW structure. Comparison to the experimental observations was performed along the a-type zone axis that is appropriate to deduce average values for the QW composition and strain.
Conclusions: The investigation concluded to the influence of growth temperature in the composition and structural properties of ultra-thin In(Ga)N/GaN QWs.

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Permalink: https://www.hzdr.de/publications/Publ-30460
Publ.-Id: 30460