Influence of strain in the reduction of the internal electric field in GaN/AlN quantum dots grown on a‐plane 6H‐SiC

Abstract

The strain state of stacks of GaN/AlN quantum dots (QDs) grown on (0001) and (1120) 6H-SiC has been investigated by means of Raman spectroscopy. Depending on the orientation of the wurtzite axis with respect to the growth direction it is found that the piezoelectric contribution to the electrostatic potential may either reinforce that arising from the spontaneous polarization or oppose it. The experimental results are compared with a theoretical model for the strain and polarization field in QDs of both orientations that allows the calculation of the electrostatic potential in the QDs. Both the experimental results and the theoretical model indicate that the internal electric field and electrostatic potential are strongly reduced in the QDs grown on (1120) 6H-SiC as compared to those grown along the wurtzite c-axis.

Anisotropic polarization of non‐polar GaN quantum dot emission

“…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. These experimental values can be now compared with those calculated considering multi-layered QDs as continuum misfitting GaN inclusions inside an infinite AlN matrix [10]. The values obtained by this model for 4 nm-separated pyramidal QDs with a base diameter and height of L x = L z = 40 nm and L y = 1 nm, ε xx = -2.1%, ε yy = +1.5%, and ε zz = -3.5%, compare well with the experimental ones for all components but that along the caxis, where the model only accounts for elastic strain relaxation.…”

“…In the present study, Raman scattering has been employed to determine the strain in the GaN QDs. This technique allows resolving the three strain components from the frequency shift of two active Raman modes, when the stress along the growth direction y is assumed to be zero [10]. 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.…”

Optical properties of GaN/AlN constant total effective radius multi-wells quantum rings

“…In the meantime, we have not included the effect of the influence of strain on the electronic and optical properties of CTER-MWQRs. Because, by means of Raman spectroscopy the strain state of GaN/AlN QDs has obtained previously (Cros et al 2006). Its influence on the internal electrostatic potential has been analyzed and found that the piezoelectric and spontaneous contributions have opposite sign, partially cancelling each other (see conclusion part of Ref Cros et al 2006).…”

Improving the emission efficiency of MBE-grown GaN/AlN QDs by strain control

“…However, due to the very narrow growth window, it was difficult to grow high-quality GaN bulk and QDs. Cros et al reported GaN/AlN QD growth on a-plane 6H-SiC [8,9]. This method suffered from an extremely expensive substrate, and compared with the GaN and AlN bulks grown on c-plane, the crystal quality still needed to be improved.…”