Gate Leakage in AlGaN/GaN Heterostructure Field Effect Transistors and Its Suppression by Novel Al_2O_3 Insulated Gate(<Special Issue>Heterostructure Microelectronics with TWHM2003)

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In order to clarify the mechanism of gate leakage in AlGaN/GaN heterostructure field effect transistors (HFETs), temperature (T)-dependent current-voltage (J-V) characteristics of Ni/n-AlGaN Schottky contact were measured in detail Large deviations from the thermionic emission transport were observed in I-V-T behavior with anomalously large reverse leakage currents. An analysis based on the thin surface harrier (TSB) model showed that the nitrogen-vacancy-related near-surface donors play a dominant role in the leakage through the AlGaN Schottky interface. As a practical scheme for suppressing the leakage currents, use of an insulated gate (IC) structure was investigated. As the insulator, Al_2O_3 was selected, and an Al_2O_3 IG structure was formed on the AlGaN/GaN heterostructure surface after an ECR-N2 plasma treatment An in-situ XPS analysis exhihited successful formation of an ultrathin stoichiometric Al2 03 layer which has a large conduction hand offset of 2.1 eV at the Al_2O_3/Al_<0.3>Ga_<0.7>N interface. The fabricated Al_2O_3 IG HFET achieved pronounced reduction of gate leakage, resulting in the good gate control of drain currents up to V_<GS> = +3 V. The maximum drain saturation current and transconductance were 0.8 A/mm and 120 mS/mm, respectively. No current collapse was observed in the Al_2O_3 IG-HEETs, indicating a remarkable advantage of the present Al_2O_3-based insulated gate and passivation structure.
社団法人電子情報通信学会の論文
2003-10-01

Gate Leakage in AlGaN/GaN Heterostructure Field Effect Transistors and Its Suppression by Novel Al_2O_3 Insulated Gate(<Special Issue>Heterostructure Microelectronics with TWHM2003)

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