Surface-related drain current dispersion effects in AlGaN-GaN HEMTs

• Published in: IEEE transactions on electron devices Vol. 51; no. 10; pp. 1554 - 1561
• Main Authors: Meneghesso, G., Verzellesi, G., Pierobon, R., Rampazzo, F., Chini, A., Mishra, U.K., Canali, C., Zanoni, E.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01-10-2004; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Activation energy; Aluminum compounds; Aluminum gallium nitrides; Applied sciences; Charge carrier lifetime; Devices; Dispersions; Drains; Electronics; Exact sciences and technology; Gallium compounds; High electron mobility transistors; MODFETs; Polarization; Semiconductor device modeling; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Surface chemistry; Transistors; current collapse; Small signal behavior; Surface current; Temperature effect; Two dimensional model; device simulation; Valence band; Transients; High electron mobility transistor; AlGaN-aN HEMTs; Drain current; Numerical simulation; Drain voltage; Time constant; Activation energy; Hole traps
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/TED.2004.835025

Drain current dispersion effects are investigated in AlGaN-GaN HEMTs by means of pulsed, transient, and small-signal measurements. Gate- and drain-lag effects characterized by time constants in the order of 10/sup -5/-10/sup -4/ s cause dispersion between dc and pulsed output characteristics when the gate or the drain voltage are pulsed. An activation energy of 0.3 eV is extracted from temperature-dependent gate-lag measurements. We show that two-dimensional numerical device simulations accounting only for polarization charges and donor-like traps at the ungated AlGaN surface can quantitatively reproduce all dispersion effects observed experimentally in the different pulsing modes, provided that the measured activation energy is adopted as the energetic distance of surface traps from the valence-band edge. Within this hypothesis, simulations show that surface traps behave as hole traps during transients, interacting with holes attracted at the AlGaN surface by the negative polarization charge.