X-ray diffraction studies of selective area grown InGaN/GaN multiple quantum wells on multi-facet GaN ridges

The structural properties of InGaN/GaN multiple quantum wells (MQW) were studied using synchrotron based high resolution x-ray diffraction (HRXRD). MQW structures were grown on the top and sidewall facets of triangular and trapezoidal shaped GaN ridges by metalorganic vapour phase epitaxy (MOVPE) in the regime of selective area growth (SAG). Period and strain variations as a function of oxide mask width were determined for both the sidewall and the top facet growth. Oxide mask widths ranged between 2 and 20 μm with openings between adjacent masks of 4 and 6 μm. Analysis of the x-ray diffraction curves revealed a sidewall / vertical growth rate ratio of ∼0.3 through a comparison of the top to sidewall facet MQW periods. Masks orientated along the 〈11-20〉 crystallographic direction showed stronger growth enhancement along with large global strain for MQW growth on the top (0001) plane. Interpreting our results within the framework of vapour phase diffusion revealed that inter-facet migration of group-III species needs to be taken into account.