图形硅衬底GaN基发光二极管薄膜去除衬底及AlN缓冲层后单个图形内微区发光及 应力变化的研究

研究了图形硅衬底上外延生长的氮化镓(GaN)基发光二极管(LED)薄膜、去除硅衬底后的无损自由状态LED薄膜以及去除氮化铝(AlN)缓冲层后的自由状态LED薄膜单个图形内的微区光致发光(PL)性能, 用荧光显微镜与扫描电镜观测了去除AlN缓冲层前后LED薄膜断面弯曲状况的变化. 研究结果表明: 1)去除硅衬底后, 自由支撑的LED薄膜朝衬底方向呈柱面弯曲状态, 且相邻图形的柱面弯曲方向不一致, 当进一步去除AlN缓冲层后薄膜会由弯曲变为平整; 2)LED薄膜在去除硅衬底前后同一图形内不同位置的PL谱具有显著差异, 而当去除AlN缓冲层后不同位置的PL谱会基本趋于一致; LED薄膜每一位置的PL 谱在去除硅衬底后均出现明显红移, 进一步去除AlN缓冲层后PL谱出现程度不一的微小蓝移; 3)自由支撑的LED薄膜去除AlN缓冲层后, PL光强随激光激发密度变化的线性关系增强, 光衰减得到改善.

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.