This paper describes a deep investigation of the degradation mechanisms induced by off-state and on-state stress in AlGaN/GaN HEMTs. Concerning reverse-bias degradation, results underline that the exposure to reverse-bias stress can induce (i) a recoverable change in the gate current due to the accumulation of negative charges under the gate, (ii) and a permanent degradation of gate characteristics due to the generation of vertical parasitic leakage paths through the AlGaN layer. Further analysis of the kinetics of this degradation mechanism, correlated with time-resolved Electroluminescence (EL) measurements, allowed to define a model that explains the time-dependence of the phenomenon and the role of gate voltage as accelerating factor, providing an interpretation for both recoverable and permanent modifications of the main device characteristics induced by reverse-bias stress. On the other hand, on devices that have shown an improved robustness against the reverse-bias gate degradation, we investigated the origin of the degradation under on-state stress. In this case, results obtained with a combined electrical and optical analysis, showed that on-state stress may induce a significant decrease in drain saturation current and Electroluminescence (EL) signal, with a degradation rate that strongly depends on the EL intensity measured before stress, which is representative of the presence of hot-electrons in the channel. On-state degradation can be ascribed to a decrease in the electric-field, due to the trapping of electrons within the barrier or at the surface induced by hot-electrons. Therefore, by using the EL signal as measure of the stress accelerating factor, it was possible to derive an acceleration law for hot-electron degradation on GaN HEMTs.

Degradation of AlGaN/GaN HEMT devices: Role of reverse-bias and hot electron stress

MENEGHESSO, GAUDENZIO;MENEGHINI, MATTEO;STOCCO, ANTONIO;BISI, DAVIDE;DE SANTI, CARLO;ROSSETTO, ISABELLA;ZANANDREA, ALBERTO;RAMPAZZO, FABIANA;ZANONI, ENRICO
2013

Abstract

This paper describes a deep investigation of the degradation mechanisms induced by off-state and on-state stress in AlGaN/GaN HEMTs. Concerning reverse-bias degradation, results underline that the exposure to reverse-bias stress can induce (i) a recoverable change in the gate current due to the accumulation of negative charges under the gate, (ii) and a permanent degradation of gate characteristics due to the generation of vertical parasitic leakage paths through the AlGaN layer. Further analysis of the kinetics of this degradation mechanism, correlated with time-resolved Electroluminescence (EL) measurements, allowed to define a model that explains the time-dependence of the phenomenon and the role of gate voltage as accelerating factor, providing an interpretation for both recoverable and permanent modifications of the main device characteristics induced by reverse-bias stress. On the other hand, on devices that have shown an improved robustness against the reverse-bias gate degradation, we investigated the origin of the degradation under on-state stress. In this case, results obtained with a combined electrical and optical analysis, showed that on-state stress may induce a significant decrease in drain saturation current and Electroluminescence (EL) signal, with a degradation rate that strongly depends on the EL intensity measured before stress, which is representative of the presence of hot-electrons in the channel. On-state degradation can be ascribed to a decrease in the electric-field, due to the trapping of electrons within the barrier or at the surface induced by hot-electrons. Therefore, by using the EL signal as measure of the stress accelerating factor, it was possible to derive an acceleration law for hot-electron degradation on GaN HEMTs.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11577/2693088
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