Transconductance Overshoot, a New Trap-Related Effect in AlGaN/GaN HEMTs

DC characteristics of AlGaN/GaN HEMTs with different thickness values the undoped GaN channel layer were compared. An abnormal transconductance ( ${g}_{m}{)}$ overshoot accompanied by a negative threshold voltage notation="LaTeX">${V}_{\text {TH}}{)}$ shift was observed during notation="LaTeX">${I}_{\text {DS}}$ – {GS}}$ sweep in devices thinner layer. At same time, non-monotonic increase gate current observed. In OFF-state, electron trapping occurs or at GaN/AlN interface, leading to positive {TH}}$ shift. When device is turning on sufficiently high , de-trapping due trap impact-ionization; consequently, and therefore {D}}$ suddenly recovers, notation="LaTeX">${g}_{m}$ effect. These effects are attributed impact-ionization consequent modulation device’s electric field.