Multi-channel GaN varactors and their current conduction mechanisms

In this work, we demonstrate multi-channel GaN varactors with enhanced quality-factor (Q-factor) and cutoff frequency (f0) and present a comprehensive investigation of their current conduction mechanisms. The varactors were based on 1x-, 2x-, and 3x-channel GaN-on-SiC epitaxy with excellent channel conductivity, showing great enhancement of ∼270% both in Q-factor and in f0, thanks to the reduced resistance and capacitance by multi-channels in AC conduction. The DC leakage current (I) in the three types of devices is dominated by Poole-Frenkel (PF) emission and trap-assisted tunneling, before the depletion of the topmost channel and after the depletion of the bottommost channel, respectively. The I in multi-channel devices is dominated by two-dimensional variable range hopping of electrons along the vertical direction between channels, when the topmost channel is depleted while the bottommost channel is not. The analysis is supported by excellent agreement between experimental results and theoretical models, along with activation energies (EA) quantitatively and statistically determined, presenting a promising technology with key understandings for future performance enhancement.