Mechanism of Interaction between Hydrogen and the Two-dimensional Electron Gas in AlGaN/GaN High Electron Mobility Transistors

The large polarization difference between AlGaN and GaN causes a two-dimensional electron gas (2DEG) to form at the interface between the two semiconductors. Capacitance-voltage (CV) measurements revealed a charge density of 4.71x10$^{12}$ electrons/cm$^{2}$ in our 60 nm Al0.2Ga0.8N on 1.5 microns of GaN heterostructure. Exposure to hydrogen in the presence of a catalyst (Pt) resulted in a marked increase in the conductivity through the 2DEG. An interface state passivation mechanism is proposed as the most probable cause of this phenomenon. This mechanism was modeled using a self-consistent Schr\"{o}dinger-Poisson solver, which showed that the passivation of interface states causes the shift of the Fermi level towards the conduction band, thereby increasing the carrier density of the 2DEG by 9{\%}. In-situ CV measurements showed a 16{\%} increase in the carrier density and a non-parallel shift in the CV curve when hydrogen was introduced, indicating in a change in the number of available states. This supports interface state passivation as a cause of the increase in the conductivity through the 2DEG.