Improvement of Channel Mobility in Inversion-Type n-Channel GaN Metal–Oxide–Semiconductor Field-Effect Transistor by High-Temperature Annealing

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Inversion- and depletion-type GaN metal–oxide–semiconductor field-effect transistors (MOSFETs) were fabricated on p- and n--type GaN epitaxial layers, respectively, grown on n+-type on-axis 4H-SiC(0001) substrates. After gate SiO2 was deposited by plasma-enhanced chemical vapor deposition at 350 °C, high-temperature annealing in N2 was carried out to modify the interface. The channel mobility was enhanced with increasing annealing temperature. The device annealed in N2 at 1100 °C after SiO2 deposition showed an inversion channel mobility of 108 cm2$\cdot$V-1$\cdot$s-1 at a gate voltage of 15 V. The authors also fabricated MOS capacitors on n--type GaN and characterized the interface state density at the SiO2/GaN interface from capacitance–voltage measurements using the Terman method, of which density was estimated to be in the range of $(6--10)\times 10^{11}$ cm-2$\cdot$eV-1 at an energy level of 0.2 eV below the conduction band edge. The interface state density tended to decrease with increasing annealing temperature, resulting in the improvement of the channel mobility.
2008-10-25