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Article Dans Une Revue Journal of Applied Physics Année : 2006

Current conduction and saturation mechanism in AlGaN/GaN ungated structures

J. Kuzmik
  • Fonction : Auteur
S. Bychikhin
  • Fonction : Auteur
D. Pogany
  • Fonction : Auteur
E. Morvan
  • Fonction : Auteur

Résumé

Current conduction and saturation mechanisms in ungated AlGaN/GaN/SiC transfer length method test structures with contact-to-contact distance L varying from 2to32µm are investigated. Current-voltage (I-V) characteristics are measured in the pulsed and in the direct current (dc) regimes. The pulsed characteristics were evaluated for the pulse duration of 50ns, and together with the dc ones show that the current saturation value depends on the contact distance and the current saturation occurs at an electrical field ~150kV/cm. This behavior contradicts the theoretical expectation valid for the ungated structures. An analysis of the I-V characteristics shows that the dc saturation current values are up to 5.5 times lower than those under the pulsed conditions for the same L. If the self-heating effect was supposed to be responsible for this observation, an unrealistic temperature rise would be required. This together with the observed ~1s long transition time into the steady state, which is several orders of magnitude longer than what one can expect for the thermal transient, excludes the dominant role of the thermal effects in the current saturation mechanism. A model of the current conduction and saturation mechanism is suggested where the charge injection from the contacts and charging of the AlGaN surface are responsible for a AlGaN/GaN channel depletion. Thus the saturation mechanism is similar to that occurring in gated structures. The model explains well the observed dependencies and is further validated by a transient interferometric mapping method. This thermooptical method operated under the pulsed conditions allows to evaluate the free carrier concentration profiles along the structure channel and to make the comparisons with the concentration below Ohmic contacts. A strong channel depletion effect has been observed for the structure with L=32µm in comparison to the negligible surface depletion effect found in the L=2µm structure. This is in full agreement with the suggested model of the current saturation mechanism and with the measured I-V characteristics.
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hal-00154930 , version 1 (22-10-2021)

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J. Kuzmik, S. Bychikhin, D. Pogany, Christophe Gaquière, E. Morvan. Current conduction and saturation mechanism in AlGaN/GaN ungated structures. Journal of Applied Physics, 2006, 99, pp.123720-1-7. ⟨10.1063/1.2207572⟩. ⟨hal-00154930⟩
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