Quantum Capacitance in N-Polar GaN/AlGaN/GaN Heterostructures

We investigate the effects of quantum capacitance in an N-polar GaN/AlGaN/GaN heterostructures by directly measuring quantum displacement of the electron wavefunction Δd. A comparison between electrically and microscopically measured thicknesses showed negative quantum displacement effects in the inverted high-electron-mobility-transistor (HEMT) structure. As a result of the quantum capacitance effects, a quantum displacement Δd of ~ -4nm was extracted from the measurements. Further analysis using 1-D self-consistent Schrodinger-Poisson solver has been done to validate the measured data. Our simulation results, including multiple-subband occupancy, explain the increasing capacitance in the measured C-V profile in N-polar GaN-based HEMTs.