Polytype Replication in Heteroepitaxial Growth of Nonpolar AlN on SiC
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defect density AlN and control of the conductivity of AlN. However, recently, Taniyasu et al.2 reported the room-temperature operation of AlN p-n-homojunction LEDs with emission wavelengths of 210 nm. Although the reported external quantum efficiency was quite low (on the order of 10–6 %), this result suggests a future directions of DUV LEDs. In the device reported by Taniyasu et al., the AlN epilayer was grown on a 4H-SiC (0001) substrate. The AlN layer contained a high density (109 cm–2) of threading dislocations (TDs). As mentioned earlier, it is necessary to reduce the TD density and employ a carrier confinement structure such as a QW structure to improve the internal quantum efficiency. Here, one must pay attention to the strong internal electric fields in AlxGa1–xN/AlN QW structures.3,4 Unlike InxGa1–xN/GaN QWs, spontaneous polarization is the main origin of the electric field in AlxGa1–xN/AlN QWs. Therefore, the only way to eliminate the undesirable electric field is to use nonpolar growth orientations.
in Heteroepitaxial Growth of Nonpolar AlN on SiC Jun Suda and Masahiro Horita
Abstract Zinc-blende and wurtzite are the most common structures for binary compound semiconductors. Aluminum nitrides (AlN), one of the most promising materials for deep ultraviolet light-emitting diodes, have a wurtzite structure as an equilibrium phase due to its strong ionicity. Silicon carbide (SiC) is widely used as a substrate for heteroepitaxial growth of AlN, since SiC has a hexagonal structure whose lattice constant is close to that of AlN. Different from other compound semiconductors, SiC can have many different crystalline structures, called polytypism. Among various polytypes of SiC, largesize high-quality wafers are available for 4H and 6H structures. When AlN is grown on a 4H- or 6H-SiC basal plane (0001), normal, wurtzite-structured AlN is obtained. On the – other hand, when AlN is grown on a nonbasal SiC plane, such as nonpolar (1100) or – (1120), what is expected? If ideal growth is realized, AlN will follow the crystalline structure of SiC (i.e., the polytype of the SiC substrate will be replicated to the AlN epitaxial layer). Nonpolar nitride growth has attracted much attention to eliminate undesirable internal electric fields due to the polarization in nitride heterostructures. In addition, nonpolar nitride growth on SiC also allows an opportunity to obtain nitrides with new crystalline structures. In this article, the polytype replication growth of AlN on nonpolar SiC substrates is reviewed.
AlN/SiC Heteroepitaxy
Introduction The thermodynamically stable phase for AlN, GaN, and InN is the wurtzite structure. InxGa1–x N/GaN, quantum well (QW) structures grown on the basal plane (c-plane) exhibit strong internal electric fields due to the piezoelectric and spontaneous polarization. These internal fields result in reduced lower internal quantum efficiency, which hinders the realization of high-efficiency green light-emitting diodes (LEDs). To avoid this problem, much attention has recently been given to nonpol
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