Surface State Spectrum of AlGaN/AlN/GaN Extracted from Static Equilibrium Electrostatics

We extract an AlGaN surface state spectrum with a density ( ${D}_{\text{SS}}$ ) ranging between $1.4\times10$ 12 and $4.7\times10$ 12 eV-1cm-2. The low ${D}_{\text{SS}}$ is achieved with in situ SiN passivation. ${D}_{\text{SS}}$ is extracted from ungated AlGaN/AlN/GaN heterostructures with varied AlN thicknesses between 0 and 2 nm: increased AlN thicknesses in heterostructures monotonously increase two-dimensional electron gas (2DEG) densities ${N}_{\text{sh}}$ and AlGaN surface potential energies ${q} {\varphi } _{\text{s}}$ , and ${D}_{\text{SS}}$ is extracted with $\boldsymbol {\Delta } {N}_{\text{sh}}$ - $\boldsymbol {\Delta } {\varphi }_{\text{s}}$ correlations. The ${D}_{\text{SS}}$ extraction methodology in this work features calibrated polarization charge values, Hartree approximation-based 2DEG profile calculation, and incorporated C-doped GaN (C-GaN) substrate impact on 2DEG. We also extract the charge neutrality level at the AlGaN surface, which is 0.95 eV below conduction band minimum.