Technology for Advanced Focal Plane Arrays of HgCdTe and AlGaN by Li He Dingjiang Yang & Guoqiang Ni

Author:Li He, Dingjiang Yang & Guoqiang Ni
Language: eng
Format: epub
Publisher: Springer Berlin Heidelberg, Berlin, Heidelberg

Considering the component unevenness of AlGaN from the growth mechanism, it is clear to see from Fig. 4.63d a completely columnar growth of AlGaN, with the columnar size about 1–2 μm. From the surface topography of Fig. 4.63a, the sample surface is composed of hexagonal layered islands as well as some border strip pits. In conjunction with Fig. 4.61, the size of domain boundary in the CL image is larger than that of the islands in the SEM image, indicating an island growth process of AlGaN. As the growth continues, the size of the islands reduces but the components remain unchanged. As we can see from Fig. 4.64, a possible growth of AlGaN can be inferred from these patterns. A low-temperature AlN buffer layer is grown on the sapphire substrate and nucleation begins (Fig. 4.64a). Following the annealing process, the nucleation centers begin to grow and the nucleation density decreases, and gradually they begin to merge (Fig. 4.64b). Then the growth begins to be quasi-two-dimensional (Fig. 4.64c). However, due to the low migration rate of Al atoms in the surface, the subsequent growth of AlN layer changes to a three-dimensional model gradually. And the surface begins to show a large number of islands with a relatively large size (Fig. 4.64d). When an AlN layer is subsequently grown on the AlGaN epitaxial layer, the reflectivity of in situ monitoring curve increases due to the consolidation process of the large islands (Fig. 4.64e), and then columnar growth begins. The non-uniformity of the Al component should begin with the merger of the big islands. Prior to the growth of AlGaN, the surface is composed of many islands, and when Al atoms and Ga atoms fall on the surface, due to a larger ratio of surface migration of the Ga atom than Al atom, Ga atoms migrate more easily than Al atoms to the island border. Due to the lower rate of surface migration, most of the Al atoms could not find a location with suitable energy and piled on top of the island, showing columnar growth (Fig. 4.64f), thus causing uneven components and columnar of the light-emitting region of AlGaN layer.

Fig. 4.64A possible AlGaN growth pattern

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