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In the manufacture of semiconductor devices, cracking of heterostructures has been recognized as a major obstacle for their post-growth processing. In this work, we explore cracked GaN/AlN multi-quantum wells (MQWs) to study the influence of pressure on the recombination energy of the photoluminescence (PL) from the polar GaN QWs. We grow GaN/AlN MQWs on a GaN(0001)/sapphire template, which provides 2.4% tensile strain for epitaxial AlN. This strain relaxes through the generation and propagation of cracks, resulting in a final inhomogeneous distribution of stress throughout the film. The crack-induced strain variation investigated by micro-Raman spectroscopy and X-ray diffraction mapping revealed a correlation between the spacing of the cracks and the amount of strain between them. We have developed a 2D model that allows us to calculate the spatial variation of the in-plane strain in the GaN and AlN layers. The measured values of compressive in-plane strain in the GaN QWs vary from -0.4 % away from cracks, to -0.7 % near cracks. PL from the GaN QWs exhibits a clear correlation to the varying strain resulting in an energy shift of ∼ 140 meV. As a result, we can experimentally calculate a pressure coefficient of PL energy of ∼ -60.4 meV/GPa for the ∼ 7 nm thick polar GaN QWs. This agrees well with the previously predicted theoretical results by Kaminska et al. in 2016 [DOI: 10.1063/1.4962282], which were demonstrated to break down for such wide QWs. We will discuss this difference with respect to the reduction in both the expected point defects and extended defects resulting from not doping and growth on a GaN template, respectively. As a result, our work indicates that cracks can be utilized for investigating some fundamental material properties related to strain effects. 

In this work, we study the thermal evolution of the optical and electrical features of an InN thin film. By correlating photoluminescence (PL) and Hall effect results, we determine the appropriate values of the correlation parameter to be used in the empirical power law that associates the electron concentration with the linewidth of the PL spectrum, in the scope of the Burstein–Moss effect across a wide range of temperatures. Additionally, by associating Raman and PL results, we observe the thermally induced compressive strain widening of the bandgap of the InN film. Our findings demonstrate the reliability of optical methods in providing contactless measurements of electrical and structural features of semiconductors.