Anisotropic strain relaxation in a-plane GaN quantum dots

Abstract

Articles you may be interested inStructural anisotropic properties of a-plane GaN epilayers grown on r-plane sapphire by molecular beam epitaxy Medium energy ion scattering ͑MEIS͒ has been used to measure at the monolayer scale the strain profile of self-organized GaN quantum dots grown on ͑11-20͒ or a-plane AlN by molecular-beam epitaxy. By confronting the MEIS results with a structural analysis carried out by atomic force microscopy, it is established that the strain profile is anisotropic, i.e., fully elastic along ͓1-100͔ and a combination of plastic and elastic along ͓0001͔. High resolution transmission electron microscopy measurements reveal the presence of misfit dislocations with 1/2 ͓0001͔ Burgers vector, consistent with MEIS data.

Anisotropic polarization of non‐polar GaN quantum dot emission

“…The values deduced from the shift of the E 2h and the A 1 (TO) modes are ε xx = -3%, ε yy = +1.7%, and ε zz = -2.1% and reveal that the symmetry of the wurtzite c-plane is broken and that the GaN dots are strongly compressed along x and extended along the growth direction. Raman results also predict a more effective strain relaxation in the z direction, which is in good agreement with previous results showing that misfit dislocations relax part of the strain along this direction [8]. Notice that the average ε xx obtained exceeds the lattice mismatch along that direction, which could be due to the influence of the SiC substrate.…”

“…Previous experimental and theoretical investigations have established the importance of strain on the control of the electronic structure and, consequently, of the polarization of the emission in these materials [5][6][7]. Concerning non-polar nanostructures, recent structural studies have demonstrated that a-plane GaN quantum dots (QDs) undergo an anisotropic strain relaxation and can exhibit an asymmetrical shape [8]. Certainly, the combination of strain anisotropy, quantum confinement and shape asymmetry are expected to have a strong impact in the degree of polarization, as has been demonstrated in zinc-blende nanostructures [9].…”

Built‐in fields in non‐polar InxGa1–xN quantum dots

“…These dimensions are close to the experimental values found for a-plane GaN/AlN QDs [6]. Figure 1 a) shows the contour plot of φ tot (r) for a c-plane InN QD, while b) displays φ tot (r) for the corresponding a-plane system.…”

“…As a consequence of the quantum confined Stark effect, the oscillator strength of the radiative transitions is strongly reduced and is accompanied by an additional red shift of the emission [3,4]. To overcome these problems, the growth of nanostructures along non-polar directions has been proposed [5,6]. However, and in contrast to the case in non-polar quantum wells (QWs), quantum dots (QDs) are three dimensional objects, and therefore still retain facets along the [0001] direction, even when grown on a non-polar substrate.…”

Piezoelectric properties of zinc blende quantum dots

“…Since these problems arise from the growth along the polar c-axis, there has been a rapid increase in the analysis of nitride-based QD systems where the c-axis lies within the growth plane [4][5][6]. Experimental data on the optical properties of these non-polar nitride-based QDs indicate that the built-in fields are in fact reduced compared to a c-plane system [5].…”