The mechanism of reverse gate leakage in AlGaN/GaN high electron mobility transistors was discussed. It was shown that trap-assisted tunnelling dominates below temperature ∼500 K, and direct tunnelling dominates at higher temperatures. The results showed that trap concentration of ∼1013 - 10-3, and trap bandwidth of ∼50%-70% of barrier height located 0.4-0.55 V below the conduction band edge.

Shreepad Karmalkar

Department of Electrical Engineering

D. Mahaveer Sathaiya

Bandwidth

Concentration (process)

Electron Traps

Electron tunneling

Gallium nitride

Gates (transistor)

High temperature effects

Leakage currents

SEMICONDUCTING ALUMINUM COMPOUNDS

Thermionic emission

Conduction band edge

high electron mobility transistors

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IIT Madras

Mechanism of the reverse gate leakage in AlGaN/GaN high electron mobility transistors

Applied Physics Letters

We elucidate five considerations for accurate estimation of electron tunneling from the gate edges of high-electron mobility transistors (HEMTs). These considerations are listed as follows: 1) edge roughness; 2) net charge at the AlGaN/passivation interface; 3) dielectric constant of the medium above the HEMT surface; 4) nontriangular potential barrier; and 5) negligible angular tunneling from the gate edge. Using these considerations, we calculate the reverse gate current IG of AlGaN/GaN HEMTs based on thermionic trap-assisted tunneling (TTT) and direct tunneling (DT) mechanisms. These calculations establish that the observed rise in IG for a gate voltage beyond the threshold is due to tunneling from the gate edges. The calculations also show that the TTT mechanism can predict the measured G of AlGaN/GaN HEMTs over a wide range of gate voltages and temperatures and point to the possibility of a rapid rise in IG at high gate voltages due to the DT mechanism. © 2007 IEEE.

IEEE Transactions on Electron Devices

Edge effects on gate tunneling current in HEMTs

We provide following important clues for resolving the reverse gate leakage mechanism in AlGaN/GaN high-electron mobility transistors (HEMTs), based on two-dimensional (2-D) simulation and analysis. First, measurement of the gate current-12-voltage, IG-VG characteristics on devices having different gate structures, passivation layers and interface charges, can reveal the field sensitivity of this mechanism. Second, of the different mechanisms proposed so far, namely - direct tunneling (DT), direct tunneling through a thin surface barrier (DTTSB) and trap-assisted tunneling (TT), DT/DTTSB is sensitive to the 2-D field, while the TT is not. Finally, the DT/DTTSB mechanism appears unlikely, since its 2-D calculations fit the measured IG-VG shape, only if we assume a physically unrealistic voltage-variable charge at the interface and/or the TSB layer. © 2006 IEEE.

IEEE Electron Device Letters

On the resolution of the mechanism for reverse gate leakage in AlGaN/GaN HEMTs

We propose two models of electron tunneling from metal to a semiconductor via traps. In addition to the electrons below the metal Fermi level, the models also include the thermally activated electrons above the Fermi level. The first model is called generalized thermionic trap-assisted tunneling (GTTT), which considers tunneling through both triangular and trapezoidal barriers present in metal insulator semiconductor (MIS) structures. The second model is called thermionic trap-assisted tunneling (TTT), which considers tunneling through triangular barriers present in modern Schottky junctions. The GTTT model is shown to predict the low field leakage currents in MIS structures with nitrided oxide as insulator, and the TTT model is shown to predict the reverse gate leakage in AlGaNGaN high electron mobility transistors. © 2006 American Institute of Physics.

Journal of Applied Physics

Thermionic trap-assisted tunneling model and its application to leakage current in nitrided oxides and AlGaN/GaN high electron mobility transistors

A novel HEMT configuration based on the RESURF technique is proposed for very high voltage power switching applications. It employs a p-n junction below the 2-DEG channel and two field plates, one extending from the gate and the other from the drain, to distribute the electric field over the gate to drain separation. 2-D simulations indicate a breakdown voltage &gt; 1 KV at on-resistance of ∼1 mΩ-cm2 (neglecting contact resistances) for the device.

RESURF AlGaN/GaN HEMT for high voltage power switching

Japanese Journal of Applied Physics

Large Gate Leakage Current in AlGaN/GaN High Electron Mobility Transistors

Gate leakage current mechanisms in AlGaN/GaN heterostructure field-effect transistors

Handbook of Thin Film Devices

GaN-Based Pyroelectronics and Piezoelectronics

AlGaN/GaN high electron mobility field effect transistors with low 1/f noise

Journal	Applied Physics Letters
ISSN	00036951
Open Access	No