The Peculiarities of Strain Relaxation in GaN/AlN Superlattices Grown on Vicinal GaN (0001) Substrate: Comparative XRD and AFM Study

Abstract

Superlattices (SLs) consisting of symmetric layers of GaN and AlN have been investigated. Detailed X-ray diffraction and reflectivity measurements demonstrate that the relaxation of built-up strain in the films generally increases with an increasing number of repetitions; however, an apparent relaxation for subcritical thickness SLs is explained through the accumulation of Nagai tilt at each interface of the SL. Additional atomic force microscopy measurements reveal surface pit densities which appear to correlate with the amount of residual strain in the films along with the appearance of cracks for SLs which have exceeded the critical thickness for plastic relaxation. These results indicate a total SL thickness beyond which growth may be limited for the formation of high-quality coherent crystal structures; however, they may indicate a growth window for the reduction of threading dislocations by controlled relaxation of the epilayers.

Integral Monolayer-Scale Featured Digital-Alloyed AlN/GaN Superlattices Using Hierarchical Growth Units

“…In general, by precisely controlling growing units of AlN and GaN monolayer (ML)scale epilayers below their equilibrium critical thickness, AlN/ GaN structures can be coherently grown and the introduced strain in the alloyed substitution can be stabilized without relaxation. 18 However, the difficulties for digital alloying AlN/ GaN heteroepitaxial growth exist because of the nonequilibrium nature of the metal organic vapor-phase epitaxy (MOVPE) technique, and the limits of operating temperature lead to inevitable vapor-phase prereaction and surface roughness for single atomic layer growth. It turns out that preparing digital-alloyed AlN/GaN structures by controlling temperature and pressure of the MOVPE process is unlikely to be realized.…”

Single-crystal halide perovskites: Opportunities and challenges

“…Facet, strain, and superlattice engineering Epitaxial growth has been widely used in the semiconductor industry. 130,131 Through the epitaxial technique, high-quality single-crystal halide perovskite nano-/microstructures with different crystallographic facets and orientations, [132][133][134] lattice strain, 135,136 and superlattice structures 137,138 have been grown, enabling many new avenues of fundamental studies and device applications.…”

Nanoscale Electrostructural Characterization of Compositionally Graded AlxGa1–xN Heterostructures on GaN/Sapphire (0001) Substrate

“…8 However, in all previous studies, the polarization-induced doping results from the compositional grading of Al from x Al = 0 → x Al = 10 -30%. In a previous work, 9 we showed the possibility of growing graded Al x Ga 1-x N coherently strained to GaN substrate with starting Al concentrations of x Al > 0%, creating an additional way for tuning the polarization-induced doping carrier densities in graded Al x Ga 1-x N layers. Indeed, growth of graded Al x Ga 1-x N coherently strained to GaN starting with an Al concentration, x Al > 0%, can modify the strain profile due to the lattice-mismatch at the interface.…”