Influence of strain on emission from GaN-on-Si microdisks

Strain-relaxation effects in AlN-buffered GaN/InGaN microdisks pivoted on Si posts of varying radii have been studied by micro-Raman spectroscopy and scanning near-field optical spectroscopy (SNOS). With increasing undercut beneath the microdisks by chemical wet-etching, the mitigation of biaxial tensile stress is found to be dependent on the contact areas between the Si posts and GaN microdisks. Strain-relaxation reduces the quantum-confined Stark effect (QCSE) in the quantum wells (QWs), leading to an 18.3% enhancement in InGaN QW internal quantum efficiency (IQE). Light out-coupling is also improved in the suspended regions owing to reduced optical absorption at AlN/Si interface compared to the central region. Meanwhile, spectral blue-shifts of ~45.6 meV are observed from the near-field photoluminescence (nf-PL) spectrum towards the edge of the microdisk. Such localization of strain relaxation can be exploited for precise strain engineering of the microdisks. The emission wavelengths of the microdisks can be stabilized by balancing strain-relaxation effects with thermal effects.