Changes of micro zone luminescent properties and stress of GaN-based light emitting diode film grown on patterned silicon substrate, induced by the removal of the substrate and AlN buffer layer

At present, there are mainly two kinds of methods to prevent crack and reduce tensile stress of the silicon substrate GaN based light emitting diode (LED) epitaxial films: one is to use the patterned silicon substrate and the other is to grow a thick AlGaN buffer layer. The two kinds of methods have their own advantages and disadvantages. Although the patterned silicon substrate GaN based LED has industrialized and is gradually accepted by the market, there remain many scientific and technical problems, to be resolved, and a lot of research gaps worth studying deeply. Among these problems, to clearly investigate the different micro zone photoluminescence and the stress states in a single-patterned GaN based LED film grown on patterned silicon substrate. The studies of the stress interaction between the buffer layer and the quanturn well layer and the effect on the luminescent properties have important guiding significance for improving the quality and performance of the devices. Different micro zone photoluminescence (PL) properties in single-patterned GaN-based LED films grown on patterned silicon substrates, nondestructive free-standing LED thin film after removing away the silicon substrate, and the free-standing LED films after removing away the AlN buffer layer are studied. The variations of the bending degree of the free-standing LED thin films before and after removing away AlN buffer layer are inverstigated by using fluorescence microscopy and scanning electron microscopy. The results show as follows. 1) After removing away the silicon substrate, the free-standing LED film bends to the substrate direction in a cylindrical bending state. After removing away the AlN buffer layer, the LED film bends into flat. 2) For LED thin films on silicon substrates or off silicon substrates, their PL spectra have significant differences in different micro zones for the same pattern. When the AlN buffer layer is removed from the substrate its PL spectrum tends to be consistent in the different micro zones of the same pattern. When the patterned silicon substrate GaN-based LED thin film is removed from the silicon substrate, the PL spectrum is redshifted in each micro zone. After AlN buffer layer is removed from the substrate, the PL spectra present different degrees of blueshift in each micro zone. 3) The LED films before and after removing away the AlN buffer layer show some differences in droop effect.