Temperature effect on Al predose and AlN nucleation affecting the buffer layer performance for the GaN-on-Si based high-voltage devices

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An AlN buffer layer allows epitaxial growth of GaN on silicon substrates. We have studied the early AlN nucleation stage performed at high and low process temperatures. We show that the temperature has a crucial effect on the chemical reactions on the Si substrate during the initial growth stage. We have observed that large clustered defects are formed at 1000 °C. These defects are responsible for degradation of the vertical leakage current (VLC) blocking capability of the buffer layer. Formation of the defects is prevented if the temperature is lowered to 800 °C, which is explained by a carbonization of the Si surface. Formation of the SiC interlayer leads to the stable AlN/Si(111) interface during subsequent high-temperature growth of the buffer structure. We demonstrate that very low VLCs in superlattice-based buffer are achieved using the low-temperature nucleation process, which makes it suitable for fabrication of high voltage AlGaN/GaN high electron mobility transistor devices.