Dependence of GaN Defect Structure on the Growth Temperature of the AlN Buffer Layer
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1068-C03-13
Dependence of GaN Defect Structure on the Growth Temperature of the AlN Buffer Layer Yuen-Yee Wong1, Edward Yi Chang1, Tsung-Hsi Yang2,3, Jet-Rung Chang2, Yi-Cheng Chen2, and Jui-Tai Ku4 1 Material Science and Engineering, National Chiao Tung University, 1001, Ta-Hsueh Rd., Hsinchu, Taiwan 2 Electronics Engineering, National Chiao Tung University, 1001, Ta Hsueh Rd., Hsinchu, Taiwan 3 Microelectronic and Information System Research Center, National Chiao Tung University, 1001, Ta Hsueh Rd., Hsinchu, Taiwan 4 Electrophysics, National Chiao Tung University, 1001, Ta Hsueh Rd., Hsinchu, Taiwan ABSTRACT The defect structure of the GaN film grown on sapphire by plasma-assisted molecular beam epitaxy (PAMBE) technique was found to be dependent on the AlN buffer layer growth temperature. This buffer growth temperature controlled the defect density in GaN film but had shown contrary effects on the density of screw threading dislocation (TD) and edge TD. The density of screw TD was high on lower temperature buffer but low on the higher temperature buffer. Meanwhile the density of edge TD had shown the opposite. Further examinations have suggested that the defect structure was closely related to the stress in the GaN film, which can be controlled by the growth temperature of the AlN buffer. Using the 525oC AlN buffer, optimum quality GaN film with relatively low screw and edge TDs were achieved. INTRODUCTION The wide bandgap GaN material has generated huge interest in the recent years due to its potential to fabricate high power and high frequency high electron mobility transistors (HEMTs). Metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) are among the most commonly used methods to achieve high quality GaN material. Currently, GaN materials are normally produced using MOCVD especially for the light emitting diodes (LEDs) application due to its high production capability. But for the high performance electronic devices, MBE may be the method of choice. Researchers have shown that GaN with best electrical properties were grown by MBE [1-3]. The advantages of MBE include the in-site diagnostic technique using RHEED for real-time crystal growth monitoring, a carbon-free and hydrogen-free growth environment, smooth surface, sharp interfaces and low point defect density. However, to achieve high quality GaN material using MBE has it own difficulties. Unlike the availability of high quality GaAs substrate for the growth of GaAs devices using MBE, the lack of large-size native substrate for GaN has resulted in growing GaN on a foreign substrate such as sapphire, silicon carbide and silicon. Due to the large mismatches in crystal lattice and thermal expansion coefficient, the GaN films grown on these substrates are associated with large density of dislocation. Furthermore, the relatively lower growth temperature of MBE as compared to that of MOCVD also causes the MBE grown GaN to have lesser quality. The typical growth temperature of MBE (700-800oC) is only about one third of the GaN melting
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