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
⁻¹
cm
⁻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.