Direct QV Interface State Spectroscopy of SiN/AlGaN/GaN HEMTs by Photo Assisted Corona non-contact CV

Deep and shallow interface states at the dielectric AlGaN interface dominate current collapse, Vth instability, and DC to RF dispersion in AlGaN GaN HEMTs. Deep states in the bandgap are frozen at room temperature, requiring photo assisted CV for direct quantification. Conventional photo assisted CV returns differential Dit(E) but determines Qit(hν) and Q2DEG only through integration of CV curves, requiring full CV acquisition and model dependent conversion of small signal capacitance into absolute interface and 2DEG charge.

In this work, non-contact corona Kelvin CV (CnCV™) is applied to perform photo assisted CV (PA CV) characterization of SiN AlGaN GaN HEMT structures together with extraction of the full electrical parameter set. This represents the first application of photo assisted CV using a non-contact corona based CnCV approach on SiN passivated AlGaN GaN HEMTs, enabling direct charge based interface state spectroscopy without metal contacts or device fabrication. CnCV directly measures charge Q through calibrated corona dosing while a Kelvin probe records the corresponding surface potential, making QV the primary measurement. Direct access to Q enables determination of (a) the 2DEG sheet density (Q2DEG) from the cumulative Q up to the pinch-off transition, (b) the full HEMT electrical parameter set derived from the QV characteristic: VP, CSiN, EOT, Ctotal, and electrical tAlGaN, and (c) deep interface state spectroscopy by PA CnCV using a single derivative Dit(E) = d(ΔQit)/d(hν), where ΔQit is measured directly in deep depletion giving an absolute photoionized interface charge at each photon energy with no device physics model.

On an example 850 Å SiN / Al0.3Ga0.7N (~20 nm) / GaN HEMT, one CnCV sweep yields CQ curves (Fig. 1a, four representative wavelengths shown) from which Q2DEG = −1.05×10^13 q/cm^2 is directly extracted and the deep-state Qit (Fig. 1b) is determined from the illumination-induced shift in deep depletion. PA CnCV at 1.32–3.35 eV (940, 870, 631, 525, 454, 370 nm) probes EC−1.4 to EC−3.0 eV, with Dit ranging from 1.4×10^11 to 3.6×10^12 cm−2 eV−1.

A single CnCV measurement delivers a complete HEMT electrical parameter set, photoionized charge Qit(hν) and the deep interface state spectrum Dit(E), enabling inline qualification of epi and passivation at full-wafer scale without device fabrication or mercury-probe contamination.