Articles you may be interested inResponse to "Comment on 'Carrier trapping and current collapse mechanism in GaN metal-semiconductor field effect transistors'" [Appl. Phys. Lett.86, 016101 (2005)] Appl. Phys. Lett. 86, 016102 (2005); 10.1063/1.1844604 Photoionization cross-section analysis for a deep trap contributing to current collapse in GaN field-effect transistors J. Appl. Phys. 96, 715 (2004); 10.1063/1.1753076Carrier trapping and current collapse mechanism in GaN metal-semiconductor field-effect transistors Mechanisms of current collapse and gate leakage currents in AlGaN/GaN heterostructure field effect transistorsTwo-dimensional transient analyses of GaN metal-semiconductor field effect transistors ͑MESFETs͒ are performed in which a three level compensation model is adopted for a semi-insulating buffer layer, where a shallow donor, a deep donor, and a deep acceptor are included. Quasipulsed current-voltage ͑I-V͒ curves are derived from the transient characteristics and are compared with steady-state I-V curves. It is shown that when the drain voltage V D is raised abruptly, the drain current I D overshoots the steady-state value, and when V D is lowered abruptly, I D remains at a low value for some periods, showing drain-lag behavior. These are explained by the deep donor's electron capturing and electron emission processes quantitatively. The drain lag could be a major cause of current collapse, although some gate lag is also seen due to the buffer layer. The current collapse is shown to be more pronounced when the deep-acceptor density in the buffer layer is higher and when an off-state drain voltage is higher, because the change of ionized deep-donor density becomes larger and hence the trapping effects become more significant. It is suggested that to minimize the current collapse in GaN-based FETs, an acceptor density in a semi-insulating layer should be made low, although the current cutoff behavior may be degraded.

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Two-dimensional transient analyses of AlGaN/GaN high electron mobility transistors (HEMTs) are performed in which a deep donor and a deep acceptor are considered in a buffer layer. Quasi-pulsed current-voltage (I-V) curves are derived from the transient characteristics. When the drain voltage is raised abruptly, electrons are injected into the buffer layer and captured by deep donors, and when it is lowered abruptly, the drain currents remain at low values for some periods and begin to increase slowly as the deep donors begin to emit electrons, showing drain-lag behavior. The gate lag could also occur due to deep levels in the buffer layer, and it is correlated with relatively high source access resistance in AlGaN/GaN HEMTs. It is shown that the current slump is more pronounced when the deep-acceptor density in the buffer layer is higher and when an off-state drain voltage is higher, because the trapping effects become more significant. The drain lag could be a major cause of current slump in the case of higher off-state drain voltage. It is suggested that to minimize current slump in AlGaN/GaN HEMTs, an acceptor density in the buffer layer should be made low, although there may be a trade-off relationship between reducing current slump and obtaining sharp current cutoff.

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The two-dimensional analysis of breakdown characteristics in field-plate AlGaN/GaN high electron mobility transistors with a relatively short gate length and short gate-to-drain distances is performed by considering a deep donor and a deep acceptor in a buffer layer. It is shown that when the acceptor density in the buffer layer is high, the breakdown voltage is determined by the impact ionization of carriers, and it can decrease with increasing the field-plate length. This is because the distance between the field-plate edge and the drain becomes very short and the electric field there becomes very high. On the other hand, when the acceptor density in the buffer layer is relatively low, the buffer leakage current becomes very large and this can determine the breakdown voltage, which becomes very low. In this case, the breakdown voltage increases with increasing the field-plate length.