Growth, characterization and fabrication of AlGaN/GaN high electron mobility transistors on silicon carbide substrates

Emen, Ayça
Wide bandgap semiconductor technology for electronics have received great attention over the last several years. Heterostructures composed of aluminium gallium nitride (AlGaN) and gallium nitride (GaN) are promising candidates for the fabrication of high power and high frequency devices due to their superior material properties. Silicon carbide (SiC) is the most suitable substrate for GaN growth because of its high thermal conductivity and lower lattice mismatch with GaN compared to silicon and sapphire. This thesis investigates the epitaxial growth of AlGaN/GaN heterostructures using metal organic chemical vapor deposition (MOCVD) on 6H-SiC substrates and further application of these heterostructures as high electron mobility transistor (HEMT) devices. In the first part of the thesis, the growth of highly resistive GaN on SiC was optimized. Resistivity values as high as 1011 Ω/sq was obtained from electrical measurements. Secondly, on the optimized GaN buffer, AlGaN/GaN heterostructures with different aluminium contents from 17 to 31% were grown. Structural and electrical characterizations have been done. Heterostructures revealed full width half maximum (FWHM) values of ~300 and ~350 arcsec for GaN and AlGaN, respectively, indicating a good crystal quality. Furthermore, the two dimensional electron gas (2DEG) mobilities between 1150-1643 cm2/V.s, sheet concentrations on the order of 1013 cm-2 and sheet resistance values between 273 and 464 Ω/sq were obtained. Finally, HEMT devices were fabricated from AlGaN/GaN heterostructures and DC output and transfer characteristics were measured. The AlGaN/GaN HEMT device with an aluminium content of 31% exhibited maximum drain current density of 1210 mA/mm, while a peak transconductance of 288 mS/mm and breakdown voltage of 14 V was achieved. .
Citation Formats
A. Emen, “Growth, characterization and fabrication of AlGaN/GaN high electron mobility transistors on silicon carbide substrates,” M.S. - Master of Science, Middle East Technical University, 2014.